Human Information Processing

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Pages 24-76.


Reading Responses

Tiffany Lee - 2/18/2013 2:01:41

1) Models are a great way to describe information that is complicated and messy in a clean and understandable way, allowing us to make better use of the information. This model, specifically, allows us to approximately predict user-computer interaction. This model can help us figure out how to present the output in a way that is easy for the user to comprehend. Another use of this model could be to help us figure out if a task is too challenging, physically or mentally, for the user to accomplish.

2) The Model Human Processor seems to focus on the basic physical interaction between the user and the computer. It is not able to capture aspects of the interace that include feelings, emotions, and aesthetics. This model also focuses on specific interactions of the interface rather than the design of the interface as a whole.

Soo Hyoung Cheong - 2/18/2013 12:46:22

1) The overall purpose of constructing a model of human cognition and action such as the Human Model Processor is to allow step by step analysis of how human’s perception, decision, and motion work alongside each other (in terms of time). This model provides simpler breakdown of the three steps, making it easier for analysis. The model can be used to determine the number of cycle times it would take for user in using particular design of the user interfaces. These can be broken down and analyzed into the three part cycles, making the analysis much simpler.

2) One limit of the Model Human Processor is that it fails to recognize outside factors that may influence the cycle times in the Model Human Processor. Another is that the Model Human Processor can give an estimate of the cycles. Not every Human Mental process are recognizable as full “cycles” which may result it underestimation or overestimation of the cycle times. It fails to capture the full complexity of computer applications when breaking down the application piece by piece and doing cycle analysis.

Joyce Liu - 2/18/2013 13:18:26

1) The overall purpose of constructing a model of human cognition and action such as the Human Model Processor is that it helps to predict human performance and evaluate design. An engineer faces much uncertainty when he is solving a problem, and the Model Human Processor provides three versions of parameters for the engineer to think about when designing the system. The three versions are 1) worst performance, 2) best performance, and 3) nominal performance. It can be helpful in the design of human interfaces because we can design interfaces based on the predictions from using equations that predict how humans will act. An example in the reading included button placement, like if we know that the user alternates between hitting the f key and 5 key, given two locations we can plug in their distances into Fitts’ law to calculate the more optimal location for the placement of the f key. Models of memory can be useful for the design of user interfaces as well because it can direct the designer in figuring out the frequency and approach to presenting information that will help the user remember.

2) The aspects of interacting with computer applications that the Model Human Processor fails to capture include interreuptability, errors, multi-tasking, and automaticity. We need to understand the cognitive processor’s control discipline before we can understand thoroughly the aforementioned issues. Interruptability, errors, multitasking, and automaticity are all relevant to interacting with computer applications, as we could be multitasking while using the application. Additionally, some features of the computer application perhaps should be automated in order to streamline processes and enhance the user’s experience. Also, humans do not always act rationally, which can pose a problem to the Model Human Processor because it assumes rationality.

Linda Cai - 2/18/2013 16:49:35

The overall purpose of constructing such a model is to put human cognition and action in a form appropriate for analyzing human-computer interaction. It can be used to approximate cognitive behavior and make engineering calculations suitably. With a model for human cognition, it can also aid in task analysis and other calculations for human-computer interaction. It gives us a way to discover how knowledge must be structured in order to be useful and easy to operate. It also gives us a framework to evaluate how usable a user interface is, by allowing the designer to predict human reaction and task completion times. The model can be used to evaluate the user interface design’s learnability and error rates using the model to do calculations for the average user (Middleman) and a upper/lowe bound users (Slowman-Fastman). It is also useful for iterative design, since it can be repeated throughout the design processes and there are no users or prototype required to use the model. The model can also be used to provide or develop guidelines for user interface design. For example, it can calculate the probability that a user will be able to bring needed information from long-term memory into working memory, having encountered the information while using the interface. Calculations using the model can also be used to create guidelines for the layout, response rates, color, button sizes, etc.

The Model Human Processor is a simplified model of human cognition, and does not take into account further complexities of the human memory or external factors unrelated to the human and interface at hand. The model assumes spontaneous decay over time and interference as the mechanisms that cause memory-retrieval failure, however it fails to take into account other possibilities such as displacement of old items by new ones, or distractions that cause the user to miss the information altogether. It also fails to incorporate other aspects of HCI, such as feedback that takes advantage of touch (e.g. physical sensations such as vibrations). It also fails to capture motor memory which is common in repetitive motor tasks which the interface may afford. Moreover, it assumes that the user is focusing on the interface and not multi-tasking, whereas it is very common for users to be doing many different tasks unrelated to the interface all at once. Along those lines, it also doesn’t take into account external environment conditions, user surroundings, whether or not the user is concentrated on the current task, and so on.

Mukul Murthy - 2/18/2013 21:30:26

The purpose of constructing a model of human cognition and action is to understand the way people think and act and predict how they will think and act under a certain set of circumstances. This is relevant to the design of user interfaces because we can use the Human Model Processor to hypothesize what a person will do when confronted with a user interface. The three components of the Human Model Processor are all relevant and important to consider when designing interfaces. The perceptual system is necessary to make sure the user is able to identify all parts of a user interface. This would involve design decisions such as how loud a sound needs to be, what kind of contrast allows a user to see the parts, and any tactile feedback. The cognitive processor deals with the way the user interprets the pieces of the interface. For example, the reading talks a lot about working memory and chunking, and says that the capacity of working memory is about seven items. This may explain why novice users can be intimidated when they see an interface with tens or hundreds of buttons; even if the buttons are all clearly labeled (which can prompt the user to their function), it is still a lot of info to take in. However, if the buttons are grouped by something like color or function, chunking may make the interface seem less daunting. Finally, the motor system models how people can physically use the system. Interfaces that require the user to push a very small button far down in a way that hurts the finger for a critical function or require the user to double-click something faster than most humans are capable of may have been poorly designed. Using these three subsystems together and the overall model, user interface designers can predict how users will sense their options, react and decide, and how they will interact with the interface.

One of the limits of the Model Human Processor is that human beings are not exactly computers. Human beings do not always do the same exact things under the same circumstances, and humans sometimes make irrational decisions just for the sake of it. Another issue is that some things are simply difficult to model, such as the decay of memories. Trying to track memories is a very inexact science, and while the model attempts to plot decay graphs for memories, humans don't always follow the model. One of the aspects of interacting with computer applications that the Human Model Processor fails to capture is the fact that, ignoring touch screens, the inputs and outputs are usually fixed. The output is almost always a flat screen display of a certain size, and the inputs for most applications are usually a keyboard and standard mouse. Another issue is that different people have different conditions - some people may have impaired vision, color blindness, or other disabilities that are not easy to account for.

Christina Hang - 2/19/2013 0:18:16

A model of human cognition can be used to provide insight and predict user-computer interactions. The model is useful for the design of user interfaces, because it provides information on how users react to visual and auditory stimuli and how memory is used to process these stimuli. Also, the model suppresses in-depth detail so the designer can easily view the system as a whole and visualize how the system behaves overall. The analysis of the three interacting subsystems of the Model Human Processor will help designers make decisions regarding the layout of the interface and distances between buttons or other controls on the interface. Although the Model Human Processor can provide a good analysis of how the human mind processes information, the timings associated with each subsystem are only estimates. Hence, the designer must design for the “slowman” and “fastman” as well as the “middleman”. Since secondary effects causes the calculations of human performance to differ from the nominal value, the “middleman” speed, then the designer should account for the extreme cases, the “slowman” and “fastman” speeds. The model is unable to capture these secondary effects, and the calculations can span a wide range.

Tiffany Jianto - 2/19/2013 10:36:58

1) The Model Human Processor helps us understand, predict, and calculate human performance that is relevant to human-computer interaction. The purpose is to be able to calculate human interaction with technology in such a way that it serves a specific purpose; for example, motion pictures need a frame rate which is calculated perfectly so that the illusion of movement appears to the watcher. In addition to being useful for perception, the model is also useful for listening or sound, to see how fast people hear and interpret sounds; for causalities, to see illusions of collisions between objects; reading, to see how fast a person can read text on a screen with different models; motor skills, mainly movement of the hand towards a target and keystrokes (which helps with figuring out the distance to place between objects); decisions, including simple and choice reaction times; and physical, name, and class matches,

2) Ranges of Fastman, Slowman are set by extremes, and the range can be negatively wide, so the calculations on performance may not be very accurate. Also, even though it is useful to calculate the speed at which people interact with computer applications, that’s all it can do. It cannot tell you the advantages and disadvantages of speeds, nor can it tell you what is better than the other. All the Model Human Processor can do is to calculate speeds and time ranges, but it cannot give any more information about any other aspect, including exact times, advantages and disadvantages, and emotional or psychological calculations.

Haotian Wang - 2/19/2013 12:24:18

1) The purpose of designing such a model is so that engineers can predict how humans will be able to perform on certain actions based on memory, speed, accuracy, etc. It is useful for engineers to know these kinds of predictions because it can inform the engineer on how to construct a system to best take advantage of known human-performance, and to judge whether systems already created are a good fit given what we know about human performance. One way in which such a model is useful for designing user interfaces is to judge how long an automatic alert needs to stay on the screen in order for a slow-man user to comprehend all the text on the screen based on speed of reading, cognition, and memorization.

2) I think the model human processor fails to adapt to the limiting factor of human habit-making. It seems to me that if systems were designed around optimizing for such basic time-calculations as retina-movement and see-think-react cycles, it fails to take into account many other of the usability heuristics which involve the entire user experience. MHP doesn't tell you whether an error occuring frequently would be a usability problem, or whether the same function being in different places in different pages would be a consistency problem. It can focus on making the computer as efficient as possible given human information-processing, but that only scratches the surface.

Ryan Rho - 2/19/2013 15:21:26

1) What is the overall purpose of a constructing a model of human cognition and action such as the Human Model Processor? What are the different ways in which such a model can be useful for the design of user interfaces?

The overall purpose of constructing the model is to organize the description of human cognition and action and understand how it works so that we can apply to the study of human-computer interaction. The model gives you scientific approach of understanding humans' behaviors with a mixture of psychology and mathematical equations.

I believe this kind of model is helpful for observing the behaviors of the disabled such as the paraplegic and blind. Since the model already has established observations such as Fitt's Law and Hick's Law, we can estimate that the behaviors of the disabled may be slower than the observations we have, indicating what how a normal person acts in a certain case.

2) What are the limits of the Model Human Processor? What aspects of interacting with computer applications does it fail to capture?

Although it is a great approach in that we obverse human's behaviors and thought process with a scientific method with numbers and figures, I believe Model Human Processor seems to focus too much on numerical values which are counterintuitive. I believe solely using this model to a study of human-computer interaction may result in limiting other methods or models to support this model because the model's foundation is heavily based on relating facts into numerical values.

Some aspects of human-computer interaction do not heavily depend on scientific facts. For example, skeuomorphism needs more of artistic values with some observations of real-life objects. Features from skeuomorphism may not be as efficient as placing features by following the Model Human Processor approach. However, skeuomorphism works in a sense that humans already have already intuitively learned how to use real-life objects that cannot be translated into numbers.

Elizabeth Hartoog - 2/19/2013 15:30:58

The human model processor is a scientific way to model how a quickly a human can react to certain stimuli. In the case of an application, we can calculate how reaction times to things on the screen, how efficient pushing a series of buttons is in one design versus another, and how to help the user remember key information related to using an application. All three of these aspects of the human model processor can be combined to make relevant and interesting calculations on how a human will interact with your application. For specifically user interfaces, it is a matter of how efficient your interface is to use. The model does not necessarily take into account how easy it is to learn the model, but rather how efficient it is to use it assuming an expert (kind of like how they calculated the keyboard times). But this brings up one aspect of how the model falls short. For example, you may have an application that pop ups an on screen keyboard for whatever reason. You can use the model to calculate how long it would take to type in a generic 12 letter password through different keyboards assuming letter placement etc. However, this does not take into account that if you use a QWERTY keyboard some people will have faster reaction times than if you used an alphabetical. This can be incorporated by using the uncertainty principle of a fashion. But this is just a particular example to demonstrate that the human model processor makes assumptions about the user using the rationality principle.

On that topic, the rationality principle assumes the human will take the most rational route to a goal. However, one cannot assume those goals are rational. Thus if an interface is designed in what is mathematically the most efficient manner, this ignores the fact that the human user may have no intention of learning how to be efficient or how to use certain aspects of the interface. In other words, the user may be lazy or uninformed. Thus certain design decisions made for efficiency may actually make the interface more difficult to use for the new and unskilled with the interface.

The model also has a strict interpretation of working memory versus long term memory to calculate cognitive cycles. Thus in situations where an application, especially mobile applications which are used in situations of high interference (receiving a phone call/text, real life obligations), you cannot necessarily make solid assumptions about working memory. Thus you cannot assume continuous use though the application should be continuously accessible. Thus in the interface design, this may change how long or how accessible past information is on screen compared to an application say on the computer or in a working environment.

Alice Huynh - 2/19/2013 16:18:03

The reading states “qualities important for Model Human Processor to possess if we are to address the practical prediction of human performance.” By interpreting how a fastman, slowman, and middleman reacts to certain perceptual sensory actions a person is able to predict just the parameters that are necessary for an average human being to perceive your user interface the way that you would want it to be perceived.

Fitts’s law states the estimated amount of time for a person to react by bringing their arm to the desired object. Using this estimation can help with designing of distance between very important user interface buttons or menus. If the time necessary for a person to react is too short of a time then the user interface is flawed.

Also a the human memory system has a capacity so a user interface that requires the user to memorize a lot of different functions might not be a great user interface. This has a lot to do with the “telephone example” from our first reading regarding how to “hold calls”. Certain telephones required the user to memorize random number combinations in order to put callers on hold. This memorization can take a large toll on the human memory system and so it is best to not leave a lot of important functionalities of a user interface up to memory retrieval which we learn is a big process of Working and Long-Term memory.

2) What are the limits of the Model Human Processor? What aspects of interacting with computer applications does it fail to capture?

One thing that this model doesn’t take into account is the ability to measure the user’s “happiness” or ability to use the user interface without any adverse effects. The reading talks a lot about how fast or how slow a user can respond to certain stimuli. One thing that can not be easily calculated is the willingness of the user to wait or the extent of how “satisfied” the user is. For instance, what if a designer focused their user interface on the “slowman”. If a user happens to be a “fastman” they might be annoyed with an extended amount of wait time.

Also a lot of the reading depends on the user having 100% concentration on the task at hand. Now a lot of users can’t focus on one thing for too long and will start to multi-task. The calculations in the reading don’t take into account the reaction time of users that could possibly be focusing on other tasks while attempting to do another action.

Jeffery Butler - 2/19/2013 16:41:32

1) Constructing a Human Model Processor helps developers understand how fast to display images, how quickly people can listen and retain the information, how fast things should happen in order to appear consequentially of each other and how fast a reader can read. The model is also useful in related a new interface that utilize long term cognitive memory. For example, in the text pg 40, the author refers to Encoding Specificity Principle where an interface (in this case computer-imaging file) has a Dark color the user will associate this differently than files with a light color making a distinction without cognitive overload. A popular case with this principle would be with affordances. The Human Model can also be helpful in relation to Fitt’s Law. With this law in place a developer can understand that if they make the more commonly used affordances farther away from others, the user will spend more cognitive power trying to operate the far affordances. An example of Fitt’s Law is the qwerty keyboard. 2) The Human Model Processor is limited by its equations. For example, if a user was reading an interface in on a busy street, the perceptual model will be consciously aware of its surroundings therefore the user’s perception will have less power used towards the interface. Hence, the interface can be perceived as more complicated than if it were viewed in a lab in front of a bunch of testing engineers. Another area of limitation is based around what has the user actually have stored in their long term memory. For example, some of the easiest interfaces (Iphone) seemed to be mind-blowingly difficult for my grandfather to fathom due to the fact that he did not have any Long term memory in relations to interfaces. Concluding, regardless if an interface utilizes the data extracted from the Model Human Processor; the interface can still be perceived as unclear and complicated.

Sumer Joshi - 2/19/2013 17:46:57

1) Fitt's Law says that the time to move a hand towards the target depends on the ratio of the distance to the target's size. The overall purpose of constructing a model of this caliber is to understand how the flow of information is picked up visually by the user and processed through cognition, and then through motor control. The flow of information allows the user (in the realm of user interfaces) to pick up the natural feeling of reading, processing, and moving a pointer (let's say a finger) to go click a button on the interface itself. The cyclical process give the user the opportunity to mainstream the process of uploading a photo in Instagram, or understanding and applying the concept of emailing a picture in the Camera application of the iPhone. Another way the Processor Model is useful is by making moving around on the interface easier for the user due to Fitt's Law. You want to keep similar actions or actions that follow other actions in a relatively close distance from each other. This leads into the user going through all of the three steps, and calculating the probability of remembering the item that was encountered earlier.

2) One limit of the MHP is that it's based on humans. This means that the processing rate and motor function is based on an average human or user's ability to understand information, so any step or series of complex steps might not make sense to the user. The developer must take into account working memory from the user, which might detract from focusing solely on the application itself but rather putting more attention on the user than the application.

Sihyun Park - 2/19/2013 19:16:52

1. The purpose of developing a cognitive model is to create a quantitative model of how users interact with a user interface. Such model will allow the tester to grasp how much time it takes for the user to process the data presented, come up with a reaction to the data, and complete the task. In the process, one would equate human brain to a computer, calculating the time the brain takes for each steps of processing the data presented, e.g. perceptual subsystem, cognitive subsystem, and motor subsystem. Cognitive models like Human Model Processor can be useful for the design of user interfaces, because it allows the tester to estimate the performance of a user interface without conducting a formal experiment. For example, one can design a user interface for a space shuttle, but it is quite difficult to conduct an experiment in real-life. In this case, creating a cognitive model provides a cheap and quick way to estimate the performance of an interface by deriving the estimated processing time for human brain without conducting a real-life or simulated experiment.

2. The limitation of the Human Model Processor lies in its core assumption that human brain can be equated to a computer. Human brain is far limited in its capabilities compared to a computer in terms of calculation speed, and in many cases, the calculations derived cannot be applied in real life. Moreover, Human model processor fails to capture: 1. an intervention from the environment - all of the calculations assume that the user is fully immersed in the interface. However, this is highly unlikely in real-life. 2. emotional interaction with the interface - a key difference between a human brain and a computer is that the former has emotion. Often, users are influenced by the aesthetics and the "feel" of an interface, affecting how they emotionally perceive the interface, and this can have a significant influence on the user's interaction with the interface.

Kimberly White - 2/19/2013 19:55:29

1. A Human Model Processor allows designers to estimate how long various tasks will take without having to do complete user testing at every stage. It could also be used as a grounds for comparison, determining what models will be easier (or faster) for a user to use. Knowing which actions take longest (relatively speaking) can also help during the design process, as ease/speed of use can be worked in from the start.

2. It doesn't capture the human part of the equation. While people can forget things, hands take time to move, and decisions must be made, the model doesn't account for human error, for not understanding parts of the UI, or for various misconceptions. While this model can be good for getting a general (and scientific) view of things, it can't replace testing with actual users.

Raymond Lin - 2/19/2013 20:01:55

By constructing the Human Model Processor, we can attempt to simulate human interaction with a prototype interface. However, in addition to this, we could also be able to measure certain human responses when they come into contact or interact with the interface.

The Model Human Processor in the end is only statistical applications. Despite whatever models we create, we can never perfectly model human reactions/interactions. People's bias for certain habits or particular styles of interface can not be simulated by this model.

Lauren Fratamico - 2/19/2013 20:53:52

1) The overall purpose of constructing a model of human cognition is so that we can more easily study it. It gives people a way to estimate how long it takes humans to do certain tasks with out performing an experiment. With the brain, we don't really know what is going on in there, so a model allows us to estimate it. If we have a model, than we can more easily understand the limitations we need to have on our system if it needs to interact with a human user. For example, we would not want them to need to memorize a string of 100 characters in order to proceed to the next screen - this is not a task that humans are good at, and our model shows it.

2) The model will not necessarily capture atypical behavior. We might have users who perform certain tasks in times way outside of our model's estimate. It also does not take into account distractions that might arise as people work with computer applications. For example, if the model thinks that people can easily remember 3 digits, we may find that people cannot as easily perform that task if at the same time they are watching a movie and facebooking. Computer applications need to take more things into account than just the model.

Colin Chang - 2/19/2013 21:24:21

1) What is the overall purpose of a constructing a model of human cognition and action such as the Human Model Processor? What are the different ways in which such a model can be useful for the design of user interfaces?

The consequence of such a model offers human-centered-designers to quantifiably build interfaces. With it comes provable interfaces design, the ability to stress test interfaces without user-testing, and know the quantitative limits of an interface.

2) What are the limits of the Model Human Processor? What aspects of interacting with computer applications does it fail to capture?

It fails to capture any account of the locus of attention, as discussion in a previous article. Meaning, no account of how long we can pay attention to something, what counts as relavant, what affordances are afforded. Like the heuristics, it also does not paint a complete picture for a designer, since user tests still offer insights unattainable (due at least to their specificity in nature) by MHP.

Alvin Yuan - 2/19/2013 22:57:59

The purpose of having such a model is to be able to use it to predict human behavior and interaction with a device or interface. Similarly, the model allows us to analyze interfaces with a different set of metrics, the ones that pertain to the model (such as cognitive cycles or total task time). This particular model can be used to analyze UI element positioning and how that affects the time necessary to complete a set of actions. The idea of working memory can be used to determine what information users will have in their working memory and what information needs to be refreshed (by a UI element such as a text box) at what time. Finally the model also forces the designer to think about the fast, typical, and the slow user and how to satisfy the demands of all three groups.

The Model Human Processor does not have a clear notion for analyzing cognitive demands for complex tasks. When a task involves a lot of thinking, the model loses a lot of expressibility since almost all of the time required for the task falls under the cognitive cycles. Ideas such as confusion, logical reasoning, and many of the ideas in the Direct Manipulation reading such as forming an intention from goals or interpretation of output are not well defined in the Model Human Processor. It also does not consider the user's experience, such as whether it was enjoyable to use the interface, whether the user felt like he/she understood how to use the interface, etc.

Andrew Gealy - 2/19/2013 23:02:16

Modeling human cognition and action in a way such as the Human Model Processor gives us tools with which to estimate the limits and norms of human performance and perception. This is useful for the designer of a user interface in that it offers basic expectations for what people should be able to perceive, do, and remember. These models might suggest offering a reminder between screens for data that cannot be easily remembered for a short time (such as a sequence of numbers longer than 7). They might guide the visual layout of an interface by determining a reasonable size of button that can be easily hit without error. They might suggest ways to structure an interface in such a way to make use of the different human perceptual modalities and their varying strengths. They might guide how much information is presented at any one time.

The Model Human Processor gives reasonable quantifiable estimates of human capacities at specific tasks. There are many other factors in the real world that might change these performance measures in an unpredictable fashion. It does not account for various human disabilities. Furthermore, the model cannot give us information on aesthetic preferences or interfaces that humans enjoy using. Basically, it does not capture the vast majority of what makes a human computer interaction good, nor should it. The model should just be used as a tool to answer particular questions about human performance, rather than to outright guide the design process.

Kate Gorman - 2/19/2013 23:07:55

1) The purpose of constructing a model of human cognition is to anticipate how a human might use your system and be able to quantify these predictions. By testing models to ensure their accuracy, you can have a more quantitative and steadfast set of design rules by which you can measure various interfaces on. This can be useful in weighing decision on where to place certain actions and how large the buttons should be. Understanding how a human will process the interface will help you avoid confusing users or having an "un-intuitive" interface. By quantifying you have a clear means of how to fix problems, whereas individual users may be unable to pinpoint precisely what might make their usage faster or decrease the ramp up time. 2) The human processor model can only capture a mechanical interaction with the system, and fails to capture an emotional response. Is the interface aesthetically pleasing? Is it memorable? It is clear what the product is and what the company does? These are all things that are incredibly important to businesses but that the human processor model fails to encapsulate.

Tenzin Nyima - 2/19/2013 23:35:39

1) As described by Moran & Newell, like computer system, even though the description is approximate when applied to human, the human mind is also an information-processing system, and a description in the same spirit can be given for it. Therefore, the Human Computer Interaction designers can take some sort of scientific approach in their designing process. This way HCI designers can quantify why one interface is better designed than the other one. But how could this be possible? The answer is cognitive psychology - the science of understanding how human think, perceive, remember and learn. And in cognitive psychology, the most important part is to develop models of human behaviour. And for the purpose of HCI designing process, 'Model Human Processor' is so far considered the best. Therefore, as Moran & Newell mentioned, the overall purpose of a constructing a model of human cognition and action such as the Human Model Processor is to help HCI designers to understand, predict and even calculate human performance relevant to Human-Computer Interaction.

For UI designers, such a model can be useful in the area of perception, motor skills, simple decisions, learning and retrieval, and problem solving. Lets take the example on “perception” from the reading. With the help of the Human Model Processor model, you could calculate the best suitable frame rate to create the illusion of motion. Moran & Newell also mentioned that the commonly used frames rates for motion picture cameras is in accord with the result of the calculation based on the Human Model Processor model. As Moran & Newell, mentioned on Page 25, this model assumes the information processing of the human behave as a serial processor. 2) This model lags when it comes to consider parallel operation (typing, reading, simultaneous translation). This model also does not take into consideration about the environment under which human perform a task. Reading CS160 assignments at a quiet place could be very different than reading the same assignment in a very noisy place.

moshe leon - 2/19/2013 23:54:09

1) What is the overall purpose of a constructing a model of human cognition and action such as the Human Model Processor?

Since computers are essentially supposed to “think,” this model provides a familiar and accessible reference for programming: “The human mind is also an information-processing system and a description in the same spirit can be given for it … [it is] intended to help us remember facts and predict user-computer interaction…” It is an attempt to explain and interpret human thinking and decision making process, by simplifying it and explaining it in terms that we can relate to and better understand. The overall purpose is to help us build User Interfaces (amongst other things) designs that are most efficient, by analyzing possible reactions and explaining them with this set of simplified analogous terminology.

What are the different ways in which such a model can be useful for the design of user interfaces?

The Model Human Processor can provide guidelines for the most effective ways to present information, knowing how the mind processes details visually and recalls those details. It is only natural to assume that the mind stores information in order to use it at some point. Once the time comes, and the information needs to be accessed, it is also natural to assume that a fast retrieval mechanism should be in place, so we don’t ‘freeze’ while we try to escape a cage with a combination lock on its’ door, while a vicious tiger is approaching. It is all about “chunking” and encoding, and how the brain remembers. Working Memory is the first step to perception- all info is in Working Memory first, and enters Long Term Memory depending on how we encode that info. How easily we are able to retrieve a memory is directly dependent upon the way we encode the memory (there are many ways). This is why we create mnemonic devices, acronyms, rhymes, etc. to help us learn (e.g. “righty-tight, lefty-loosey”). With these thoughts in mind, it is extremely crucial that anyone who is to design a User Interface would carefully build it upon them. By understanding the ways the human mind works (i.e. simplifying it) we can predict its behavior for different scenarios, and model our design to fit these scenarios as naturally as possible and utilize them as best as possible. (“Practical prediction of human performance”)

2) What are the limits of the Model Human Processor?

It’s a simplified version of the mind; the way the human brain processes information, makes decisions, and reacts is much more complicated and nuanced: “A model so simple does not, of course, do justice to the richness and subtlety of the human mind. But it does help use to understand, predict, and even to calculate human performance relevant to human-computer interaction.” The Model Human Processor is a shadow of the human mind- an attempt to capture its essence and ‘bottle’ it into a limited set of guidelines and predictions. There are many more things, left un-captured, and perhaps even perceived in a wrongful way. It is easy to come to a wrong conclusion while adopting the Model Human Processor, since it tries, through statistics (amongst its arsenal of tools) to predict complex human behaviors and the thoughts behind them. Unlike direct mapping in Computer Science computational instruments, the human mind may have different outcome to similar scenarios with many unpredictable and unforeseen variables.

What aspects of interacting with computer applications does it fail to capture?

That the programmer has to set up the principles which the program follows- the “rules” by which a program will act based on the response of the user. These principles have to account for the many choices a human can and will make. Each person’s brain has a different storehouse of information based on knowledge and experience, something a computer application cannot replicate. Human information processing and response can also vary with physiological realities like hunger, fatigue, emotional state. It also, cannot predict the unpredictable. As strange as it sounds, there is always a new scenario at hand which might change the decision and outcome only because a single variable changed. As best as we can try to account to any possible path and obstacle alike, we are sure to have missed something(s) on the way. It also fails to acknowledge that the human mind thinks a step ahead, while the computer uses the last two steps to calculate the next.

Elise McCallum - 2/20/2013 0:16:14

1) The overall purpose of constructing a model of human cognition and action is to build a model to simulate the way that humans learn and interact with the world around them. Such a model can be useful for the design of user interfaces because it can give an idea of the cognitive process and how people will process certain parts of an interface. It can also give a good idea of how users will respond (act) to particular aspects of an interface. This can be seen in such applications as the "button," which people have come to associate with the act of pushing and maps to the cognitive function of a change occurring in the interface (i.e. the button has a function of somehow presenting new data). This has come to be an association encoded in long-term memory so that when someone perceives a "button," they know to push it with the expected output of a changed page.

2) One limit of the Model Human Processor is that it only works for the average human being. It cannot properly model someone with an exceptionally good memory, exceptionally bad memory, or distorted perceptions. It also can contain errors of association, or associations that should not be made. It fails to capture aspects of interacting with computer applications such as dealing with error as well. Since errors in an application often force a certain action (or choice from a small set of actions), this largely differs from the expected behaviour in real life and is thus not represented in the Model Human Processor. It also fails to encapsulate cognitive dissonance, or the idea that conflicting ideas can be held in one's cognition, which applies to interacting with computer applications. This comes from the idea that multiple applications may perform the same function but in different and often conflicting ways (i.e. the close button being in the upper left vs. the upper right corner).

Brian L. Chang - 2/20/2013 0:44:41

THe purpose of constructing the model like the Human Model Processor (HMP) is to evaluate how the usability of the product is, to estimate the time it takes to perform the task and to better understand the interactions between the human and the product. The model can be useful in understanding how long a user will take to do a specific task which might help you decide if this is an effective setup for the task at hand. The model can also be helpful in thinking about what the user must do in order for a task to be completed and seeing how long each part of the task takes.

    The MHP is limited by the type of the user. The reading mentions that there are slightly faster thinking users and slightly slower ones. The model tries to account for that by assigning times for the different users, but this can only go so far. The model also fails to capture hardware factors. For example, in real life different type of buttons take the user more time to get use to and in some cases they never get use to them. Users may also more quickly adapt to a task that is similar to an everyday task.

Zeeshan Javed - 2/20/2013 1:28:37

1) What is the overall purpose of a constructing a model of human cognition and action such as the Human Model Processor? What are the different ways in which such a model can be useful for the design of user interfaces?

The overall purpose of constructing a model of human cognitions is attributed to the idea that we as designers and scientists can quantity human cognition to an abstracted level that allows us to understand conditions of the human response especially in its application to user interface. It’s test to calculate how fast a human finishes a task is extremely enlightening. The Human Model Processor unlike another information-processing system divides its interacting subsystems to the levels of perception, motor response, and cognition. By understanding individual aspects to each of these three things a designer is awarded a trained mindset that considers these conditions when building a user-interface system. Because the purpose of the Human Model Processor is to outline human cognition in a way that captures the majority of individuals, it can be extremely useful and far-reaching in the methods it can incite in a designer.

2) What are the limits of the Model Human Processor? What aspects of interacting with computer applications does it fail to capture?

The Model Human Processor is limited in it’s ability to fully, accurately calculate and consider applications that are outside the means of the parameters that are consisted of in the equation. There are certain applications and inaccuracies that can be accrued within the calculation scheme. Furthermore it will fail to capture all interacting computer applications that do not focus on perception, motor response, and cognition. Systems that intertwine more than one of these also are at risk of inaccuracy.

Brett Johnson - 2/20/2013 1:41:25

1.) The purpose of constructing a model of human cognition and action like the Human Model Processor is to better understand user interactions with the computer. When we have formulas like Hick’s Law and Fitt’s Law, we are able to better understand the users’s actions, predict what their actions will be, and see how well people are using the systems we design. For example, we see from the reading that a QWERTY keyboard is slightly faster than an alphabetical one, although not by much when the power law is taken into consideration. This would help a keyboard manufacturer make design decisions in product development stages. By observing the rules laid out in this chapter, as designers we can seek to minimize the users’s efforts when using a product. We can limit the decision time needed in an interface by lessening the number of buttons, n in Hick’s Law. We can also decrease the distance between buttons or moveable items and increase their size to decrease the time it take the user to hit the button or moveable item. This observation is from an understanding of Fitt’s Law.

2.) The Model Human Processor is limited in that it cannot fully represent the complexities of the human mind and the decision processes that it utilizes. I think that one area of HCI that this model does not take into account is the emotional connection that users have when they use a software product. For example, some justify the skeuomorphic leather and stitching in Apple’s “Find My Friends” application as creating a warmer, more natural feel for an action that is inherently odd(tracking the location of people you know). This could be seen as decreasing the decision time by lessening the awkwardness of the situation and thus lessening the uncertainty about the decision (uncertainty principle).

Soyeon Kim (Summer) - 2/20/2013 1:48:15

1) A construction of models like the Human Model Processor allows us to practically calculate predictions of human (user) performance.

 An analogy can be drawn in this model for the storage and processing of a computer with perceptual, motor, cognitive, and memory activities of the users. The model can be applied to design of the user interface; UI designers can utilize the model, predicating the user’s behavior. For example, an audible stimulus (i.e. a beep) can indicate the error made by the user and flashing cursor (on screen) can show the user the location of the input. Also, the model makes it easier to make a use of logical order of the user inputs. 

2) The Model Human Processor does not take an account of deviations in its calculation (of prediction) that may come from things like mistakes made by user.

 During the interaction with computer applications, users often behave in the ways not been calculated/intended. For example, users often click on “yes” button though they clearly intended to click on “no” button. More importantly, the Model Human Processor fails to capture psychological aspect of users interaction (decisions).  

Shujing Zhang - 2/20/2013 1:57:31

Q1. 1) The purpose of constructing a human model processor is to help us remember facts and predict user-computer interaction rather than intended as a statement of what is really in the head. The processor model is intended to make approximate predictions of gross human behavior.

2) ii) Since human model processor can be divided into three subsystems: the perceptual, motor and cognitive systems, they can actually be used to simulate and predict the gross behavior of human based on the three subsystems. For perceptual phenomena, one fact is that the similar visual stimuli that occur within one Perceptual Processor cycle tend to fuse into a single coherent percept. When it involves the movement of fovea of eyes, it can dominate the time required for the task. For motor skills, the movement of hands towards a target and keystrokes are two basic kinds of movement occur in human computer interaction.

Q2. 1) The cycle time of the perceptual processor sets fundamental limits on the speed with which the user can attend to the visual and auditory input. Second, the memory acts as a limiting agent. In addition, the processing capacity, which will be allocated to different tasks is also a limiting factor, both process tasks in parallel or in serial.

2) The human processor model fails to capture the semantic description of long-term memory. In order for us to understand human performance, the semantic description of long-term should be taken into account. Second, in perceptual processor, it fails to describe the interaction of visual stimuli with intensity and distance with more detail. In Cognitive processor, it didn’t capture the control structure of cognitive processor. It is necessary to consider the processor’s control discipline if interruptability, error, multitasking or other phenomena are to be thoroughly understood.

Kevin Liang - 2/20/2013 2:05:26

1) We attempt to view and model users as a computer. For example we can think of human eyes as a visual way that inputs memory into the brain or in computer terms, the RAM. This can be applied to designing user interfaces because we want to know how a person remembers something to see how a user interface should operate. For example, underlined blue text generally means it is a link to a different page. A user actually remembers this and keeps it in mind. There is no explanation why this is so, but it just is and it works because it has been the trend that users REMEMBER.

2) The Model Human Processor focuses on the user itself and excludes external factors. For example, the environment one is in can also contribute to the interaction of a user interface. For example, if I was blind and I wanted to make a phone call, it would be totally different from a person who has eyes and can punch in numbers much easier. This is an extreme case but the model human processor focuses on the normal cases and not the extreme cases in which is a pitfall. When interacting with computer applications, the MHP fails to capture is the design of a NEW style of user interface. For example, before touch screens came out, everything was totally new and the learning curve was high. The idea of tapping onto glass was an entirely new concept, yet a revolutionary one that the MHP failed to carry out.

David Seeto - 2/20/2013 2:14:37

By constructing a model of human cognition and action such as the Human Model Processor, we provide a concrete means to measure and predict how efficiently and well a human can interact with a machine. In order words, we can evaluate the usability of a machine. By being able to calculate different parameters such as storage capacity, decay time, coding type, and cycle time, user interface designers can tweak their design to maximize efficiency. While calculated ranges may merely be estimates, they provide basic guidelines as how to design a user interface. Take for example, the need for an app to provide feedback to the user. If the content of the feedback is too dense and is shown only for a limited amount of time, a user may be unable to perceive, remember, and process such feedback. In this sense, the Model Human Processor allows designers to create apps that are within the bounds of expected human performance.

The Model Human Processor is limited in its quantitative approach. While very concrete, equations to calculate different values are not necessarily or readily applicable because it is often difficult to put information-theoretic entropy into quantitative terms. Also, while it incorporates the perception, thinking, and acting of machine operation, it merely captures the completion of one task in an ideal setting. It does not reflect on user unpredictability or user mistakes. Nor does the metaphor port over to all tasks and the use of a user interface as a whole.

Scott Stewart - 2/20/2013 2:24:23

The purpose of designing a model of human cognition is so that design problems can be solved more easily. A cognitive model provides a layer of abstraction that allows for designers to build according to a person's ability to see, hear, and react to a stimulus without needing to know exactly how the body processes these signals. This model is useful in almost every aspect of the interface design, because knowing how people interact with and perceive their surroundings covers the core functions of a user interface, such as displaying something to a user (taking advantage of the vision model), to how fast information can be displayed to be useful (using the perception, processing, and memory models).

Since the Model Human Processor is only a model, it does not include information about how events in the human body actually occur. For instance, a designer building headphones could use some of the information present in the Model Human Processor (such as what fidelity people would actually be able to hear), but the designer may also need to know how the ear actually works to perceive sound, and the Model Human Processor does not help with this. The Model Human Processor also fails to capture the emotional response of people to an interface. People may respond better to certain color schemes or a specific font, but this model does not capture this aesthetic information that is a notable part of interface design.

Cong Chen - 2/20/2013 2:55:22

1) The purpose of constructing a model of the human via the Human Model Processor is to be able to break down the abilities and limitations of the human person into mathematical and formuliac manner. As shown in the chapter through many examples, by breaking down the human in the Human Model Processor, we can address each step of the way that a human goes through when performing a particular action. As a result, we are able to with precision, calculate the response time and other useful information.

This model can be helpful for designing user interfaces in many ways. One is that by breaking down all the steps that a human goes through (From perceptual to cognitive to motor), we are able to address the difficulties and things a human may consider into the designing the interface. For instance, when trying to determine the optimal locations for buttons, with this model, one is able to break the problem down into equations and solve to get the range of time benefits for various button location. Another way this model is useful is that when designing an interface, one does not have to go out and interview people to understand how people will use it. One can simply apply this model into consideration for designing the interface in terms of the various response times and possibilities.

2) This model has limitations. I feel like this model is too structure and systematic. There are advantages to this type of model in that it is easy for a designer to consider the human limitations. However, it does not account for the "natural" variations that cannot be modeled by distributions or variance. These types of natural variations can only most accurately be obtained through interview and sampling of real people; as people still differ from this "ideal" perception of how all humans process information.

Because this model is limited by it's realism in terms of what humans would want (ex: photographers may think according to this model, etc), it fails to capture the natural aspects of humans with respect to interacting with computer applications. Some types of people may have certain habits for though processes or response times that are not standard and would not be captured in the Human Model Processor. For instance, suppose that computer scientists respond very quickly to screen fresh rates since they stare at computer screens all day. This would not be appropriate modeled by Fastman or Slowman. The most accurate way to understand how users would use interfaces would still be the interview them and ask them to learn about their habits.

Zhaochen "JJ" Liu - 2/20/2013 4:04:05


What is the overall purpose of a constructing a model of human cognition and action such as the Human Model Processor?

The goal is to understand better how human process the information that he gets from the system and how he responds to that information. Ultimately, we will use this model of human cognition and action to design effective systems and interfaces.

What are the different ways in which such a model can be useful for the design of user interfaces?

  • Better layout the interface
    • For example, according to Fitts’s Law, we can lay buttons in various places, with different sizes, based on their functionalities and relevance to the current task
  • Design things that conform to users’ conceptual model
    • For example, a good interface makes people feel confident and make them feel they have done similar things before because the interface or work flow matches their mental model.
  • More easily make user remember certain things
    • For example, by correctly use working memory and long term memory, it is possible to make sure the user remembers how to perform certain tasks more easily, thus easily accomplish it for the next time.
  • Better design the transactions between different tasks
    • For example, a sound interface does not require user to remember too much things from one interface to the following interface.
  • Calculate the response time
    • For example, in order to design the best “between time” between two clicks in a “double-click” action, you have to know how to calculate how long a user will take to carry out a task


What are the limits of the Model Human Processor?

Complexity: It is unlikely to model the human’s cognition and action with some simple math formulas very precisely. The MHP is a rough model with detailed complexities removed. The MHP only cares about some important factors and key values; however, in reality, there are a lot more going on.

Interference: People are usually dealing with multiple tasks at the same time. It is very possible that the user is engaging different things and got distracted. In this way, the MHP cannot be used to measure the underlying processing inside this user’s cognition and action.

Experiments are not perfect: It is not possible to generalize the human mental system via experiments because the human subjects have limited abilities to cope with tasks perfectly.

Ongoing debate: The study of cognition science is still an evolving process. There are much more yet to be discovered by the scientists and there are still a lot of debates about different topics.

What aspects of interacting with computer applications does it fail to capture?

  • Interacting with a lot of complex computer applications at the same time
  • Using the applications to interact with other human beings, such as online games and instant messaging
  • Problems happened during interacting with computer applications that are not caused by the design itself, but by something else (such as hardware problem, etc)

Ben Dong - 2/20/2013 4:28:26

The overall purpose of constructing a model of human cognition is to be able to approximately predict human behavior under certain situations and in response to specific stimuli. Doing this allows for generalized predictions of user-computer interactions, including the ways people perceive and interact with user interfaces. Being able to predict how users react helps designers create more intuitive interfaces.

The Model Human Processor is only an approximate description, not intended to precisely portray what goes on inside a user's mind. It is very objective and numeric in its descriptions and modeling, which allows for decently accurate generalizations. However, this purely objective modeling doesn't capture many users' potentially emotion-driven or irrational quirks. In addition, it only provides a general model based on information capacity within a user's mind, which isn't always useful during the design process of some interfaces.

Claire Tuna - 2/20/2013 4:48:26

1) What is the overall purpose of a constructing a model of human cognition and action such as the Human Model Processor? What are the different ways in which such a model can be useful for the design of user interfaces? The purpose of constructing the model is to simplify the process by which humans complete tasks. With the simplified model, we can estimate how long a task may take to complete and optimize this time by minimizing cycles of cognitive, motor and perceptual processing. For example, knowing the length of the cycle of perceptual processing helps graphics designers understand how many frames they need per second to convince the user that continuous motion is occurring. In my drawing application, the marks made by the user updated on the screen every time a the user’s finger updated its coordinates. This, in practice, took up the maximum amount of memory. Instead, if I had known the length of the visual input cycle, I could have only updated the screen every 1/cycle length seconds, or perhaps slightly more often for the Fastman user. In another example in the text, using the model of human cognition, designers were able to simulate the effect of moving a button on a calculator. The new button position theoretically decreased the amount of motor time used, according to Fitt’s Law. Using such a model, the designers were able to successfully conclude that the new button position would lead to a shorter total task accomplishment time for the user, illustrating that if user-testing resources are short, the Human Model Processor equations can provide a decent approximation. A designer could also keep the cognitive processor in mind while designing an interface. For example, he could try not to burden the user with more chunks of data than could fit in working memory. This method is employed by MasterLock, which gives you a combination in the form 12-34-56, rather than 1 2 3 4 5 6, because 3 chunks is more likely to be kept in working memory.

2) What are the limits of the Model Human Processor? What aspects of interacting with computer applications does it fail to capture?

The Model Human Processor misses the empirical side of human computer interactions. It completely fails to capture certain “feelings”, such as directness, freedom and control, feedback and visibility of system status. In fact, the Model Human Processor model would show that an interface which did not show feedback such as “Thank you for your homework submission!”, would take less time than one that did not, because the interface with feedback requires additional cycles of the visual and cognitive processors. However, because the feedback creates a feeling of comfort in the user, it is a valuable part of the interaction that should not be cut, though the MHP may suggest that this is the more efficient course of action. It also does not work very neatly to compare subtle differences in design decisions. Between two labels for a task, presumably, both would require 1 visual cycle and 1 cognitive cycle to decode. However, it’s hard to quantify the difference between the clearer label and the more confusing label. My intuition is that the main shortcoming between the 3 realms is in the cognitive processor.

Glenn Sugden - 2/20/2013 8:32:15

A Human Model Processor (HMP) is a useful tool in justifying human-computer interaction (HCI) decisions - by utilizing vast amounts of data gathered by psychologists, cog-sci researchers, etc, one can make intelligent choices when designing (or modifying) a user interface (UI). At an abstract level, you can use: the perceptual system to design systems that take into account a /typical/ person's limitations when it comes to quickly recognizing stimulus you might present, the limitations imposed by the the motor system in terms of reacting to that stimulus, and the cognitive system limitations in terms of learning to react more quickly to the stimulus with practice (and even intuition). All of these systems, as a whole, can guide a designer of user interfaces into making choices that maximize productivity, while minimizing the delays that naturally occur in human beings.

The most obvious information that is missing from the MHP is the data from differently abled people. For example, someone who is blind is very likely to react differently to audio cues that a sighted person, as a many different studies have shown that the auditory skills of blind people are "significantly better results than the sighted subjects."* Physical limitations in the motor system will (obviously) change the overall HMP picture for people with similar limitations (E.G. severe arthritis, missing digits, problems with eyesight, etc., are going to drastically lower the speed at which that person is able to type).

Eun Sun Shin - 2/20/2013 8:32:52

1) The model helps organize (into the three different subsystems--perceptual, motor, and cognitive) and make approximate predictions of gross human behavior. It also explains phenomenon that might not be clear from looking at the human cognition and action in another perspective. For example, a simple analysis in terms of the Human Model Processor was able to easily explain the results from the experiment mentioned in page 32 and 32. Such a model can be useful for the design of user interfaces because it can explain why users act or use a product a certain way (if observers are initially confused), help designers predict user behavior to better create intuitive products, and so on. 2) The limits of the Model Human Processor is that the model can only cover the parts of the human cognition that shares similarities with computers. Computers lack various tasks and features that the human body/brain/mind have. The model makes humans sound like a robot running on a set system/algorithm because it fails to take into consideration the illogical and unexpected parts/happenings of the human body/brain/mind (such as emotions, illness, and so on). One aspect of interacting with computer applications that it fails to capture is the scenario in which a user is distracted and not fully concentrating on using the app. In such a situation, the human model processor is not able to capture partial participation, which affects memory. Color blind people will also fail to interact with computer applications that have certain colors that users cannot differentiate.

Bryan Pine - 2/20/2013 8:37:01

1) From the perspective of this class, the purpose of constructing the Human Model Processor is to create a simplified metaphor for actual human perception and behavior that is very similar to the medium in which our interfaces are being designed. The full operation of the human brain is too complicated to even understand right now, and the Model Processor idea gives us something to grab onto to guide our decision-making about user interfaces. For example, the full biological process of visual perception is more than a designer has time to think about, but the simplified computer metaphor gets quickly to the important point: people can't fully take in on two things far apart at the same time. That lesson is important to the designer; he can make sure that his interface does not require the user to do what he physically cannot. The concepts of chunking and working memory capacity are also important to designers, who should not create an interface that requires the user to recall 20 different things continuously. Again, the Model Processor does not tell you anything that a full biological understanding of the human body wouldn't, but it is a useful abstraction that allows us to make decisions without knowing all the details, some of which are not even fully understood by anyone.

2) One weakness of the Model Human Processor is that modern science does not fully understand the process that is being abstracted, and many aspects of the model were derived through experimentation and observation rather than from a full understanding of the underlying process. An abstraction only has value if it allows you to make correct decisions without understanding the full process, but in this case it is entirely possible that the simplification will lead designers to make bad decisions. For example, designers often take advantage of the cognitive process of chunking when designing their interfaces. If we were unaware of this process and it were not a part of the model, designers would be stuck thinking that there were no way to expand beyond the amount of independent stimuli that could be remembered at one time, which would limit their designs. There may be other real processes, like chunking, that we do not yet understand and so are not included in the model. The Human Model Processor also completely ignores the emotional component of human-computer interaction. It assumes that the human is a computer with certain capabilities, and computers' resources and capabilities don't change in response to emotions as a human's do. The Model Human Processor is still a very useful concept, but it should be considered alongside other models that take emotional factors into account.

Weishu Xu - 2/20/2013 8:39:47

1) The overall purpose of constructing a Human Model Processor is to give designers a proxy to estimate how long it will take an individual to user a certain interface and how likely they will remember certain details of how to use or work a system. Sometimes it is difficult to have access to individuals who can test the system, and it is helpful to have an alternative tool as a gauge of how an individual would likely engage with the system. It will allow a designer of user interfaces to note and incorporate certain common rules of design that follow the patterns of human perceptual, motor, and cognitive behavior when creating the system.

2) The limits of the Model Human Processor include the fact that it does not take into account the effect of environmental conditions of humans that use the systems. Many times individuals are multitasking while performing a task or tool, which would affect their reaction time. In addition, individuals may be tired or energetic, comfortable or uncomfortable, and all of these differences in situation may affect how they are able to perform.

André Crabb - 2/20/2013 10:20:14

The overall purpose of constructing such a model is to help us understand the human mind in more detail. With this knowledge, and the numbers associated with it, we can also more accurately predict and calculate how humans might interact with a given system.This model can be useful for UI design because it gives designers some concrete numbers to consider when designing things that should be visually appealing to a user. Many examples were given in the text about how quickly a typical user can process visual data, or how quickly a user can move their arms/fingers to input data, or how quickly a user can make a decision based on what she sees. Knowledge of all this and how it relates can guide a UI designer to making an interface that is quick to use and easy to understand.

The limits of the Model Human Processor are given by the numbers. I.e. the cycle time of your perceptual processor, or the memory capacity of your working memory. All this information could guide a developer to make a theoretically perfect interface. However, something the MHP doesn't capture is the user's enjoyment of the interface. How nice does it look? How fun is it to use? The MHP doesn't tap into the emotions of humans, and just provides numbers on our performance as if we were robots.

Achal Dave - 2/20/2013 10:33:54

1) What is the overall purpose of constructing a model of human cognition and action such as the Human Model Processor? What are the different ways in which such a model can be useful for the design of user interfaces?

The general purpose of such models is to make attempts at predicting and designing for human behavior. In the MHP model, we can recognize the skills and fallbacks of the perceptual, cognitive and motor systems, and use these to decide where our interfaces need to be altered.

For example, Fitts' law tells us that since the motor system takes time to get to various interface elements, we should position the most useful ones in more accessible places (for example, being able to hit "Start" in Windows by jamming the cursor to a corner). Similarly, Hick's law, or the uncertainty principle shows us that the cognitive system takes time to process various menu choices, and we can use the entropy calculation to provide more usable menus.

In general, these models provide a glimpse into how people are most likely to use interfaces that we design, and what problems they are probably going to run into.

2) What are the limits of the Model Human Processor? What aspects of interacting with computer applications does it fail to capture?

However, while the models provide mathematical solutions to many design questions, it misses out on some of the emotional aspects of human computer interaction.

Specifically, the model says little about both the aesthetic and personal appeal of interfaces. It is easy to imagine a visually unappealing design that would still fulfill many of the principles we learn from the MHP model, but that users dislike. In other words, the MHP principles provide solutions to practical design issues, but do not cover less calculable aspects of the brain.

Questions regarding the personality of an interface are not answerable by the MHP model. What type of language do you use throughout your interface to make the user feel closer to it? What color schemes or design choices could put people into certain moods? These questions may require less mathematical, but equally important, principles.

Lishan Zhang - 2/20/2013 10:34:49

Q1: (1) Model Human Processor provides quantified information about human performance. The overall purpose of constructing this model is to learn more about the human memories and processors together with how they operate therefore try to build a machine structure that can mimic human cognition and action. In this way,

(2) We can learn many insights from Model Human Processor when we design user interfaces.

  • An interface should not expect users to remember the details in interface.
  • An interface should provide cues to help users retrieve related information from their long-term memory.
  • An interface should put the things in chunks in order to be perceived easily by the users.
  • An interface should reduce the uncertainty because it will slow down the speed of users.


  1. MHP uses structural boxes rather then a depth of processing which can affect the extend material is remembered.
  2. Instead of storing in discrete chunks by MHP, memories do have strength and can be made stronger by repetition.
  3. The experimental ways to distinguishing the differences of memory and processing is not perfect.
  4. MHP only concerns spontaneous decay and interference over time but fails to consider other interference like long-term forgetting.
  5. The Model is over-simplified to match at least three areas such as semantic description of long-term memory, the description of the Perceptual processor and the description of the cognitive processor.

Aarthi Ravi - 2/20/2013 10:51:16

The Model Human Processor helps us to understand, predict and calculate human performance relevant to human computer interaction. The different ways in which this model could be useful include: 1) The Perceptual Processor cycle could guide you in assessing the minimum time required for a human to perceive visual or audio information eg. minimum frame rate in videos 2) The Motor Processor cycle could guide a designer in determining the positioning of the keys in order to reduce time elapsed in movement off your hands to the target and the movement between keystrokes 3) The model could provide an estimate of the reaction time to perform simple calculations which could in turn help the designer design an interface to reduce work done by the cognitive processor. 4) The model provides the technique of learning and retrieval performed by the human mind. Using this knowledge a designer can design an interface that minimizes the interference from the working memory as well as the long term memory.

The parameters of the Model Human Processor could have uncertainties associated with it. These parameters could vary from individual to individual. Therefore, it is not accurate. Moreover it fails to capture certain phenomenon like fatigue and mental workload of the human brain. But most importantly it fails to aid the designer in deciding what functions the application must contain in order to carry out a certain task.

Lemuel Daniel Wu - 2/20/2013 11:00:51

1. The overall purpose of constructing a model of human cognition and action like the Human Model Processor is to relieve the user of the burden of memorizing large chunks of information, and helping the user to connect ideas together without having to remember how all of those ideas were first conceptualized in the user's brain. The Processor is also to help the user to be able to decide quickly on what he/she wants to do to minimize hassle and work on the user's part to do simple tasks.

2. The limits to the Model Human are that they don't always present information such that it respects memory strength. The Model Human Processor assumes that chunks of items are what is best remembered, but that is not always the case. The Model Human Processor also fails to take into account that some things that the user does that should be blackboxed so that the machine does it all for the human, like typing out a really long name of a person (the machine could have a text suggestion based on what keys the user has typed so far, for example).

Yuliang Guan - 2/20/2013 11:18:05

(1) The purpose of constructing a model of human cognition and action is to help people remember facts and predict user-computer interaction rather than intended as a statement of what is really in the head. Human model processor is easy to describe the memories and processors and also leave the description of the principles of operation to arise in context. The model human processor can be useful for the design of user interfaces in three ways. The preceptual system: this way consists of sensors and associated buffer memories. This system carries physical sensations into internal representations, and then the memories form a visual image store and auditory image store to hold the output. The cognitive system: it receives coded information from the image stores in its working memory and uses the stored information in long-term memory to make decision, and then the motor system makes response based on the decision. The motor system: the movement response, which the thought is finally translated into action.

(2) The model human processor is limited in the ability to deal with tasks is clear beyond doubt. One general position focuses on memory and another one focuses on processing. The processing capacity is allocated to different parts of tasks within a parallel system. Another limit is that the processing posits a serial system and permit only one operation at a time.

The model human processor cannot produce memory-retrieval successfully because it incorporates spontaneous decay over time and interference as mechanisms. The description of the model human processor may be expanded at some cost in the following areas: semantic description of long-term memory, the description of the perceptual processor, and the description of the cognitive processor.

Zach Burggraf - 2/20/2013 11:39:25

1) The purpose of the Human Model Processor is quite simply to have some way of quantifying how humans think and act. In Interface Design, we try to optimize the way our applications display information and receive information from a user. And in particular, we tend to optimize this for time. (The time it takes a user to complete the tasks our application allows them to complete.) By having a model of how much time it takes a user to view information, process it, and respond to it (mentally and physically) we can judge how good an interface is based on this time.

2) The Model Human Processor fails on two accounts. Firstly, and less obviously, it only models the "model" human. That is, it does not take into account the needs of many above and below average users, or physically and mentally handicapped users. It assumes all users will be relatively similar when it comes to using computers. The second case is more obvious I think: It doesn't say anything about, or rather fails to capture human intuition. We can measure how likely it is that a human will need to type an F compared to a Q and thus minimize the keyboard distance of the F. However, we cannot really quantify if a human will understand an interface, if an X in the corner of a window really conveys the meaning of "if I click this, the window will close".

Yong Hoon Lee - 2/20/2013 11:40:58

1. The purpose of constructing a model like the Human Model Processor is to characterize the processes of human thought and understanding in a more rigorous but also more approximate way, so as to abstract out many of the biological details regarding these concepts and focus on only the elements most relevant to one's interests. For instance, the Human Model Processor focuses on response times and general phenomena, and abstracts details such as the structure of memory away, so that one can conduct a more mathematical analysis of how efficient a certain design choice is. Another conceivable model may abstract away the response time and focus on building a more accurate model of human memory. Models like these can be useful for designing user interfaces in several ways, the most important of which has been mentioned, namely allowing researchers and designers to more quantitatively assess the characteristics of their design that are best implemented in a certain sense, such as in relation to motor response or signal processing times. In addition, such a model can help in the actual design and ideas stage, as the designer can think of the human mind in the simpler terms presented by models, and thus can focus their design so that it is best suited for the aspects of human cognition which are best exemplified by the models of his or her choice. Finally, these models can help user interface researchers develop new "best practices" for user interface design by using the models to find new leads as to how to best optimize interfaces for users. By starting this search from a more focused model of human cognition, scientists can start with a narrower base of ideas and thus more quickly find promising theories.

2. The main limit of the Model Human Processor is that it abstracts away from aspects of human cognition which do not have to do with the three processors considered in the model, and reduces the three processors to what are essentially timings. Efficiency and speed are very important things to have in a user interface, but do not capture all aspects of designing a functional user interface. One aspect which is not considered by this model is the capacity for errors in decoding the symbols presented to a user in an interface. In other words, while the model does assess how differences in representation can make certain symbols more or less efficient to decode solely based on their physical characteristics, it does not consider how humans interpret symbols and whether they may misinterpret them. For instance, some may see an arrow pointing backwards to mean "back", while others may see "undo". The Model Human Processor assumes that the symbols presented to the user can be identified, at least with practice, and thus does not take into account exactly HOW the user interprets a symbol or user interface element. Furthermore, it completely ignores the question of aesthetics in user interface design, as personal taste is a notoriously hard thing to quantify and cannot be boiled down to a processor argument. Indeed, a more aesthetically pleasing interface may take more time to use but may end up being preferable to the more efficient interface, especially in examples such as software designed for children. The question of skeuomorphism is related to this, as users may find an interface which is reminiscent of a real-life design more intuitive and easier to use. This advantage, however, can only be quantified in terms of cognition time in the Model Human Processor, and thus can be difficult to compare to a more novel interface design, as it can be hard to estimate accurate response times to many stimuli.

Kayvan Najafzadeh - 2/20/2013 11:50:38

The overall purpose of these models are to make approximate predictions of gross human behavior. And applying these approximate predictions in our design.

Monica To - 2/20/2013 11:55:49

1). The overall purpose of constructing a model of human cognition and action, like The Human Model Processor, is better understand the ways humans and computers work. By understanding how humans and computers work, we can improve the way humans and computers interact. The Human Model Processor uses the cognitive, motor, and perceptual processors along with the different memory storages to formulate a system that could help designers measure the efficiency and performance of their user interface or product. To justify their model, the authors of this reading creates an analogy between the human mind and a computer. For example, a computer's processor or information processing system is very much like the human mind. One comparison that I found intriguing was how the computer memory and disk is analogous to the human's short-term ("working memory") and long-term memory. Computers store recent and relatively new files in RAM for fast and easy retrieval and stores everythings else in disk. RAM acts as the "working memory" and costs less to retrieve than files on disk. Similarily, humans have a short-term memory, where recent and things that are frequently used are easy to access and things from the past or rarely thought of take a longer time to recall or remember. Again, if we could understand how the human mind is similar to that of a computer processor, we could better design user interfaces or increase efficiency in the product use. One way this Human Model Processor is useful in design is designing the position and placement of buttons on a UI. In the reading, Card, Moran, and Newell described the placement of the "f" button of some scientific calculators. They emphasized the importance of the location of the "f" button and that using Fitt's Law, we could see that a better location for the "f" button was probably somewhere closer to the number buttons. By this simple observation, the designer could design the layout of the buttons to be more efficient for the user. The user could calculate their equation at a faster time and more efficiently. From understanding the movement of the hand and the cognitive processor and motor processor and how many cycles it would take to correct errors or come up with decisions, the designer could create a user interface that would improve the user's experience.

2). The Human Processor model has its limits when we observe all sectors of human-computer interaction. The human processor models provides designers with a model to improve the speed and performance of an event within a certain user interface, but it fails to incorporate aspects like intuition and intent of the user. In other words, it may help a designer design a UI that will allow a user to push buttons faster, but it does not help a designer with creating a UI that is intuitive to use, asethetically appealing, or reasonable to use. The human processor model observes the cognitive, motor, and perceptual processors with the different types of memory to create a system for designers to use gauge the time a user will take to perform certain tasks it does not account for the quality of content of the application or the aesthetic appeal of it. For example, buttons may be placed in a favorable position according to the Model Human Processor, but it may be besides cluttered design elements that may distract or confuse the user. In this case, the Model Human Processor will fail to evaluate this aspect and the design will still not be very favorable.

yunrui zhang - 2/20/2013 12:00:23

1)The overall purpose of constructing a model of human cognition and action such as the Human Model Processor is that help us remember facts and predict user-computer interaction, useful for making approximate predictions of gross human behavior. Human Model Processor is useful when 1.We need to design frames of images for animation or other purposes. We can take the Visual Image Store and calculate the time span for one single percept and plan according for the frame rate. 2. When our interface need users to remember things, we can take the Short and Long Term Memory and adjust how our interface will fit the human brains' working principles. 3. When we need to place buttons on our interfaces, we should check with “Motor Skill” and place them according to Fitt's law, so that the location is more suitable for human movement. 4.When we need to represent users with choices, we can refer to the Choice Reaction Time to determine what choices we should provide. 2)Model Human Processor contains great uncertainty in many parameters, and any calculation lies in a wide range rather than having a nominal value. Also, humans are complicated machines, and one reaction are often affected by a large combination of others, as well as the outer environment. It is hard to predict human reactions using numbers only. Model Human Processor fails to capture users are often immersed in environments, which can affect greatly how users can interact with an interface. Also, users have moods and often subconscious or conscious thought processes, they may interact with how users' memory and motor responses. The Model Human Processor fails to address these.

Eric Leung - 2/20/2013 12:10:26

The overall purpose is so that when designing interfaces, we are aware of the limitations of humans and what we can reasonably expect from a human to be able to perform. Most of the ways mentioned are mental models, such as reaction time and decision time. Ways that a model can be useful is by knowing the average size of human hands, or average length of human arms in order to make things usable. Other ways is knowing the state that the user is in when using the interface, such as whether they are in a distressed state or a calmed state, or maybe a tired state using this specific interface.

Limits of the Model Human Processor are exactly as mentioned above, it fails to capture physical data about humans, and if an interface is too large or too small, it may be uncomfortable to use.

Matthew Chang - 2/20/2013 12:17:41

1) The overall purposes of constructing a model of human cognition and action is to provide insight on the basic mechanics of how humans perceive and react while also providing numbers. These numbers are important for making various design choices, such as how many frames per second are required for a smooth flowing motion picture to roughly how long an alert should appear on the screen before timing out.

2) The limits are inherent with the approximation. It attempts to assign numbers to processes that are still not entirely understood, leading to the need for extremely lax ranges of operation. This can be seen in the processing time for the various systems described.

Edward Shi - 2/20/2013 12:35:20

Arvind Ramesh - 2/20/2013 12:36:26

1. The Human Model Processor is extremely useful in that it allows an interface designer to abstract away the infinitely complex human brain and deal with it in quantifiable measurements. Human cognition is a field by itself, and modeling it as a computer processor allows a UI designer to make accurate assumptions as to how the user will behave. For example, one example given in the reading was the placement of the "F" button on the calculator. Using reaction times from the HMP, one can get an idea of the impact of changing the location of the button would be. Also, the HMP allows interface designers to get an idea of how much a user can store in their Working Memory, which would prevent them from designing programs that required the user to constantly commit things to long term memory. Yet another way the HMP is useful is that it gives the designer an idea of how to design things in "chunks" so more information can be quickly recalled by the user. Also, an interface designer could get an idea of how quick a calculation must take place for two events to be perceived as as cause-effect relationship. These are just a few of the ways the HMP can help designers develop great user interfaces.

2. The limit of the HMP is that it is just an approximation of human cognition. Variables like past experience, environment, and personal skill at a given task can throw the HMP completely off. The HMP is rather an estimation of how most users can be expected to behave based on numerous studies. For interfaces that involve many moving parts, the HMP can begin to fall apart. For example, the HMP does not take into account the attention-span of a typical user. If an interface requires its users to stay focused for long periods of time, it may still be a poor design even if it satisfies all the requirements given by the HMP. Another factor the HMP doesn't completely address is the extent to which long-term memory affects a users performance. This topic is gone over briefly, in that the user can recall information associatively, but the whole process is just too complex to fit in the HMP. The human brain is vastly different from a computer. Consequently, an interface that depends on the user constantly pulling from long-term memory might not be the best idea, even if it gives them enough time to do so.

Edward Shi - 2/20/2013 12:43:25

The purpose of constructing a model of human cognition is to better understand how the human mind works and how it connects to the actions. This is especially important for designer of user interfaces because what we are trying to achieve is an interface that allows the user to comfortably map human cognition to actions. We want that harmony of mind and action. For instance, by understanding how our eye focuses mainly in the fovea and how long it takes for it to flit around, we can better understand where to put certain buttons and relevant action buttons. By knowing what the limits and capabilities of the human mind and body, we can create an interface tailored perfectly for it. The model shows us that we remember audio better than visual. Thus we know that we can count of audio more. IT shows us that chunks are memorized more fluidly than random aggregations of words.

Of course at the end of the day, a model is still a model. There may be things that it doesn't take into account such as environment. Perhaps a person is particularly familiar with a subject and increases their ability to adapt. A target user group may have previous experience and habits that may be difficult to change despite naturally intuition that is assumed by the model. Models also tend to generalize and for specific target groups, that generalization may or may not be accurate. It may not take into limitations placed by certain factors such as a person listening to music or orders from a manager at the same time while performing the task.

Edward Shi - 2/20/2013 12:43:46

The purpose of constructing a model of human cognition is to better understand how the human mind works and how it connects to the actions. This is especially important for designer of user interfaces because what we are trying to achieve is an interface that allows the user to comfortably map human cognition to actions. We want that harmony of mind and action. For instance, by understanding how our eye focuses mainly in the fovea and how long it takes for it to flit around, we can better understand where to put certain buttons and relevant action buttons. By knowing what the limits and capabilities of the human mind and body, we can create an interface tailored perfectly for it. The model shows us that we remember audio better than visual. Thus we know that we can count of audio more. IT shows us that chunks are memorized more fluidly than random aggregations of words.

Of course at the end of the day, a model is still a model. There may be things that it doesn't take into account such as environment. Perhaps a person is particularly familiar with a subject and increases their ability to adapt. A target user group may have previous experience and habits that may be difficult to change despite naturally intuition that is assumed by the model. Models also tend to generalize and for specific target groups, that generalization may or may not be accurate. It may not take into limitations placed by certain factors such as a person listening to music or orders from a manager at the same time while performing the task.

Eric Xiao - 2/20/2013 13:00:33


1) The overall purpose of constructing a model is to try to define the way humans think and perceive concepts in the real world so that we can better understand how to design user interfaces for each particular facet and way of thinking as well as model each component of our model with a mathematical equation to give it quantitative data.

Examples of this in the reading are how we have a perceptual threshold of how many clicks we can hear per second, and our maximum motor output rate. It's a good way to construct more general principles from the data created by modeling our minds in this fashion, like how to design for the way we retrieve information from memory, and taking into account the distances between buttons and items to decrease the time it takes for us to process an action.

2) The Model Human Processor does not denote what constitutes good aesthetic design. It does note how to create illusions of real world objects, such as balls bouncing off each other, but not shapes and patterns to which we are attracted. It also does not capture our experiences and our backgrounds into the equation of user interfaces. Everything is very general with little to no context. It gives it a lot of power because it captures most people, but it fails to capture the context for more specific user interfaces and applications.

Ben Goldberg - 2/20/2013 13:02:02

1) It's helpful to model human cognition and action so that one can better understand how humans interact with their environment. This has obvious implications for user interfaces, it can for example help people understand what makes an icon clearly visible.

2) It fails to capture external factors that can effect a user using a computer, stuff that is hard to account for. Like any model, it simplifies how the real world works, which can lead to inaccurate results.

Erika Delk - 2/20/2013 13:05:05

1. Having a model of human cognition allows us to think of the mind as a system. This allows us to more easily think about what the mind can and cannot do, and makes the idea of human cognition less abstract. Because we then have a clearer idea of the limits of cognition, it's easier for us to think of what interfaces are poorly designed for our model of cognition.

2. The human model processor is limited in that it cannot capture confusion, random tries, and other things that humans tend to do when in an unfamiliar situation. Furthermore, the human model processor cannot give any insight to the aesthetics of an interface.

Shaun Benjamin - 2/20/2013 13:12:18

One main reason for constructing the Model Human Processor is that it allows us to view a human action or response to something in the framework of a familiar system. We evaluate the components that make up the Model Human Processor and estimate what reaction will follow given a certain input. Experiments are described which attempt to measure each processor's clock frequency, allowing us to make more accurate predictions based on the time we think it will take a human to process an input. We can use the model to better design user interfaces by taking into account the decay time of memory, and designing out interfaces to maximize the probability that information will be readily accessible for the user. We can attempt to provide information at a rate that maximizes the efficiency of the "recognize-act cycle" which would make the user experience as smooth as possible.

While the model is useful in some regards, it cannot be used exclusively to design effective user interfaces. In using this model to design applications, we are disregarding other outside events that may disrupt the users experience with the application. If we attempt to optimize the application based on the the Model Human Processor, it is difficult to take into account what external forces may be influencing the user. Each user is different, and may have different reaction times and different working memory capacities. Using one model as our user may make it more difficult for anyone who doesn't fit our model to use the application.

Eric Wishart - 2/20/2013 13:12:34

1) The overall purpose of constructing a model of human cognition and action is to calculate the cognitive and motor processing time using experimental methods so that we can apply statistical values to a user interface. Using these values we can determine if a user is likely to forget a key piece of information that they will need in their working memory, or how long it will take them to complete a series of actions.

2) The Model Human Process fails to capture the real world interactions that we have with computers. The model does not take into consideration distractions of the outside environment, or stopping in the middle of an interaction and coming back a few minutes later.

Derek Lau - 2/20/2013 13:14:37

In constructing a model of human cognition and action such as the Human Model Processor, it allows us to view the human mind as a simplified model that thinks and reacts like a computer system. The upside to this is that because computer systems have been studied more extensively and are manmade, the way that those systems react to certain stimuli have been proven and are more predictable, as opposed to the still relatively unknown model of the human mind. This model is useful for designing user interfaces because we can take each subsystem of the HMP and analyze their responses objectively. By using statistical measurements of response time, processor cycle time, and other such numbers, we can directly map layouts and designs of user interfaces into numerical analyses, about which we can then make a decision of whether they are desired results or not.

The MHP does not take into account many human factors, since it is a simplified model. It acts as a running average of human beings in general, failing to take into account cases (which may not be trivial) of certain human beings, such as memory issues or psychological disorders of certain people. Additionally, the MHP fails to capture certain aspects of humans that cannot be measured by numbers, such as certain interests of people that lead them to make quicker decisions or take more impulsive actions, violating the numbers measured by the MHP. This carries over to interacting with computer applications, where colors and interests of the content and layout factory heavily into the human's actions, not solely the number of choices or working memory of the human.

Timothy Wu - 2/20/2013 13:23:21

1) The overall purpose of constructing a model of human cognition and action is so that we can create an abstract model which people can use to analyze and improve upon common mental tasks. The authors of the paper call this the "spirit of the enterprise." In this context, the use of a model such as the Human Model Processor is in order to improve human-computer interaction, which has monetary and societal implications. Being able to measure the effectiveness of an interface in the enterprise can be used to create products that delight users and incentivize them to remain loyal to a company. In addition, creating great user-interfaces can advance mankind's abilities as a whole, improving their lives by making things more convenient or easier to do than they were before.

Such a model can be useful for the design of user interfaces because you can have a realistic gauge of the limits of human capacity in memory as well as motor skills. Keeping these limits in mind, you can design your interface to be as usable by humans as possible. The possibilities for creating interfaces are endless, and it is very possible to design an interface that is unusable by humans because it fails to take into account human limitations. Human limitations in memory, for instance, are useful in creating user interfaces because you want to make sure that your interface does not put a memory burden on the user so arduous that it outstrips normative human capacity. Instead, you can put indicators, reminders, and documentation in various places so that the user can reference information later.

Another instance of this is human motor skills. You want to make sure that interacting with the interface is not too fast for human perception grasp and then react to, nor do you want to make it too slow and thereby annoy your users. Instead, you want to design the interface keeping in mind normative human perceptive and motor capacity and make sure that your interface appears and feels as fluid to humans as the experience of using a real life object.

2) The limits of the Model Human Processor are that the model abstracts away many details about how the underlying human systems work. For instance, the details of perception on the physical and biological level are omitted. Another limit is how the theory represents memory in different ways. Memory is neatly divided into "boxes" in the theory, like Short-Term Memory, Long-Term Memory, Working Memory, and so forth, with their own separate registers, parameters, and transfer paths. However, there is a more subtle gestalt that exists in reality that is difficult to understand with the current technology and progress in the field.

Next, there is the limit in the notion of memory chunks versus memory strength. Some theories account for how memories can be made stronger by repetition, and others propose that memory is arranged in a system of chunks that refer to each other in a way that is conducive for memory access. It is difficult to discern what is the reality at this point, but the Model Human Processor theory simply chooses the view that memory is represented as a system of chunks.

Lastly, the theory has trouble accounting for the difference between interference and decay in the disappearance of memories. When a memory is forgotten, the theory attributes it to other information interfering with the retrieval of the memory that is sought. However, it is hard to tell whether the cause of forgetting is not due to the fact that the memory has decayed or wholly disappeared from memory. Interference assumes that memories are persistent in the mind but are unretrievable, whereas decay assumes that memories actually disappear, and it is difficult to be able to attribute it to one or the other.

The theory fails to capture the aspect of aesthetic appeal, in that the theory focuses mainly on the usability of the interface through the lens of the limits of human capacity. Aesthetic appeal is something that also greatly contributes to interacting with computer applications and is difficult to gauge using the Model Human Processor theory because aesthetics are highly subjective and qualitative. The theory attempts to be as objective and mathematic as possible so that it can have a concretely measurable framework for usability, but it leaves out an important aspect of the overall human-computer interaction equation.

Anh Mai - 2/20/2013 13:24:49

1) What is the overall purpose of a constructing a model of human cognition and action such as the Human Model Processor? What are the different ways in which such a model can be useful for the design of user interfaces?

The purpose of these kinds of model is to show that the human brain functions much like an actual computer, albeit sometimes not a very perfect/efficient one. These models help the user interface designer understand more about the general architecture of who they are designing for, and how some designs can be made to work well with this human computer - such as how to design an interface to take advantage of the fact that cognitive recognition allows users to work more efficient if they are shown familiar interfaces for similar tasks by remembering what they did before and apply it.

2) What are the limits of the Model Human Processor? What aspects of interacting with computer applications does it fail to capture?

The model is simple in its assumptions that the user, or computer, is only involved in one task at a time. If I'm only interacting with the specific interface then the situation will be perfect, but often times I have to deal with outside influence such as the environment around me or maybe I'm doing something else as well as interacting with said interface. It's like trying to make your computer run 20 different applications versus just running 1 - there is usually a difference in performance.

Jin Ryu - 2/20/2013 13:40:20

1. The purpose of constructing models like the Human Model Processor is to simulate human psychology and to calculate the performance of a human to complete a task using an application without having to spend as many resources in experiments. There are several ways in which this can be useful to designing an user interface: - perceptual system: having an idea of how a user is bound to perceive the interface is bound to be helpful. By taking this into account, applying this can lead to better visuals, audio, and easier usability. It also sets limits to what an application should be able to do before it goes out of bounds of human perception (such as showing images too fast) and the ideal average on which a normal human can handle. - motor system: how a user can actually use the interface is important. There are physical limits to what a human can do, and an application that is aware of these ranges can be much useful than one that is difficult to use regarding physical motor control (such as too tiny buttons.) There are also natural actions and mechanical behavior that can be more intuitive to people and can be used to ease the design. - cognitive system: this can be useful to a better design if it requires use of memory or logic. An interface can be frustrating to use if one has to remember things constantly (such as having to know certain keys or sequences for a lot of functions) and if it is difficult to even remember in the first place (keys and sequences are too long or are too many.) It can also be a bad design if it is complex and illogical to the human way of thought. With the HMP, designers can estimate what would be easier to memorize and the natural way in which humans process new or old information so as to provide an easier-to-use interface that does not overestimate a human's ability to reason and remember. - overall: being able to calculate how a human would fare with a user interface using the HMP as a whole would give helpful feedback to the design's usability and lead to a wiser design for better user performance

2. Some limits of the MHP model are: despite the documentation and research, it may be difficult to understand where the constraints can arise in human performance of using a design, especially if the complexities and issues may overlap between different systems of the model (or simultaneously causing problems within more than one section.) There are also some conflicts in psychology studies and alternative theoretical views on one aspect of the HMP that do not always concur. These variances in knowledge of the human brain and psychology can lead to inaccuracies of human performance while using an interface. It may also bring about unsuccessful interpretation of problems and some issues can be dealt in the wrong approach. There are theoretical complexities and understanding of human systems in such as: the structure of memory in humans, working memory span, and variation in memory (memory strength vs chunks). The model can also exhibit interference and decay, some that are hard to tell apart from each other, and there are many details in the different MHP systems that can be developed further for accuracy although it will no longer be simple then. It could fail to capture the usefulness of an app or the level of interest in a user when (s)he interacts with the computer application. There are also a diverse demographic and culture so it may fail to account for social and psychological variation among people and how they respond if the target audience for an app is very general and to a large, diverse population.

Avneesh Kohli - 2/20/2013 13:46:13

By constructing a model of human cognition and action, product and application designers are able to fine tune the user interface to take advantage of the constructs of the human brain. By having a fundamental understanding of how the brain works, interaction designers are better able to develop an interface model that correlates best with the way a human is able to perceive, store, and act upon most effectively. In particular, it allows the designer to focus on the various aspects of the interface, including the parts that the user must interpret into something understandable as well as the actionable aspects to the interface. With each of those, the designer can independently work on reducing time to completion, as the model suggests there are three different processors in the Model Human Processor. Fitt's Law, for example, gives an interface developer a great starting point for understand, physically, how long it takes a user to complete an action. Given this information, an interface can be constructed that minimizes the amount of user clicks so as to shave precious time off the overall time to completion. Overall, the Model Human Processing model gives a designer concrete data points to be able to iterate and improve on their designs in an effort to make an interface as efficient to use as possible through an understanding of how the human brain and body work.

While scientific data is often helpful in achieving measurable increase in interface quality, the Model Human Processor is not able to help us gauge what is more intuitive for a user. For example, it doesn't help us pinpoint for sure exactly which phrases or selected text in an interface resonate best with the target user group. This model is completely independent of interface context, meaning it doesn't take into account the objectives of an interface, nor does it have a specific understanding of the user group the interface will be reaching. Even further, as a scientific model, much of the formulas and data points associated with it point to an overall average of the human population, but it does not take into account special cases, where perhaps a user might be impaired in some way, or is perhaps underdeveloped. Additionally, as application interfaces start to expand beyond the traditional point and click model, and into mobile devices and wearable technology, humans will accordingly change and react differently to these interfaces, something that the human processing model doesn't entirely account for.

John Sloan - 2/20/2013 14:00:14

1) The overall purpose of constructing a model of human cognition is to use this model to approximate how a human will interact with given situations on a computer program. We can use this model to create equations for estimating how effective a given design decision will be, such as the decision of where to put a certain button on a calculator or keyboard. These equations can be estimates of a person's reaction time, or even the time it takes them to make a decision. It is also useful in that it can provide insight into how the brain and perception works in a way that makes sense to computer architects, and allows us to talk about how actions will effect a person's working memory, cognition and resulting motor actions. This is extremely useful in design and user interfaces because it creates a simple model that we can develop rules upon that guide our design decisions. For example, an app designer may be trying to choose between a few icons for buttons on the dock that most clearly associate with the desired output. The designer can run test with users to track there reaction time to see which icons were most effective in their association with the desired task. There are a multitude of other advantages to this model that all aid in making design choices based on approximations of human cognition that come from the Human Model Processor.

2) The Model Human Processor is extremely useful in predicting how efficient the design will be in terms of how fast the user will be able to make associations with buttons and the general layout. However, it seems to lack a more human element of the design process. Making an app efficient to use is not the only thing that should be taken into account, and it does not necessarily take away human error as a factor. Thinking of the brain and cognition as a computer is great for making an app designed for, well, a computer. I think its still important to have visual appeal as a factor, because the user will be more comfortable using the app for long periods of time. Also it is still necessary to keep in mind ways the user will develop bad habits based on the design. Ultimately, the Human Model Processor takes away the human element of interacting with computer applications and is only useful for predicting or calculating human 'performance' in human-computer interactions.

Brent Batas - 2/20/2013 14:03:47


The purpose of constructing such a model as the Human Processor Model is that it suppresses details that are unnecessary for communicating a design. It is useful for approximating interactions, in particular, how long it takes to complete a task, rather than describing exactly what is going on inside someone’s head. The model is comprised of three systems: the perceptual system, the motor system, and the cognitive system. In the model, information is stored as a visual image, working memory, or long term memory.

This model is useful for determining if someone will remember what they’ve done in an interface. Having users remember how to use an interface is essential to enabling them to use it efficiently in the future. Another way this model is useful is for determining the time it takes for a user to move his/her hand to a target (Fitt’s Law) based on relative precision required. This is useful for determining aspects of the interface, like how big to make buttons or other controls, what types of menus to use, and where to put items on the screen.


One limit of this model is that it does not pinpoint what makes a human have a difficult time accomplishing a task; it merely signals the presence of some kind of difficulty, or constraint. Another limitation is that the model assumes that tasks are completed in a serial (sequential) fashion, when in fact there may be cases in real life where some tasks are completed in parallel. Furthermore, the model assumes that memories are stored in discrete chunks—that is, they either exist or they do not. However, in reality, memory is actually not so discrete—memories often have errors or vary in other unpredictable ways. This model is unequipped to distinguish given a faulty memory, whether or not its quality of faultiness is caused by the system design (which would prompt a redesign) or rather simply due to the vagaries of human memory.

Jian-Yang Liu - 2/20/2013 14:05:12

1) The purpose of constructing a model of human cognition and action is to attempt to address the practical prediction of human performance by calculating the time required to perform certain tasks. This is so that we can better modify/tune user interface design to accommodate the needs and requirements of people. Because the model determines the probability that a user will remember an item that may have been encountered in the process, it’s useful because we can determine whether the user would be able to repeat the vital information through some time t, or whether we’ll need to create prompts that’ll give the user the required information, or allow them to write down the information somewhere. Further, we’ll know not to put events at too quick a pace that the user will be unable to catch the necessary information.

2) The Model Human Processor is limited mainly by the fact that development in psychological science remains primitive such that it cannot be effectively deployed for practical engineering purposes. Further, it doesn’t cover everything about the way a user deals with information. The model assumes that the user is only working on one thing at a time, which is certainly not true most of the time; the user may be talking on the phone while typing out an email. It only considers the immediate user; it doesn’t consider the effects of other people on the user, which can cause a lapse in concentration on computer applications. Finally, it cannot deal with environmental conditions that the person might be in while completing the task (running outdoors rather than sitting next to a computer).

Alexander Javad - 2/20/2013 14:07:08

1) The purpose of constructing a model of human cognition and action is to predict user-computer interaction and thus cater our designs of systems to be easily understandable and easily usable for the average user. This is useful for the design of user-interfaces because with our Model Human Processor... we can make more intelligent design decisions that will improve visibility and give users better clues as to how to operate the system we've built.

2) The Model Human Processor is, by definition, limited because it is a model... and cannot be applied to every human user. For example, if you give my 82 year old grandmother who has short-term memory loss a system that has been perfectly catered to assist our Model Human Processor in the use of our system... it still will not help because my grandmother's memory capacity will not be up to par with that of our model's... AND on top of that... she is not familiar with computer technology as me and my generation are... so she may not understand that a button affords pushing... or that a search box affords being clicked on and having text entered into it. In fact, she might not even know how to use a track pad! So in the construction of our Model Human Processor, we as user-interface designers must be wary as to our target user group and construct a model taking into account our target user group rather than building a "one-size fits all" model of the human mind and forcing our target users to fit that model.

Juntao Mao - 2/20/2013 14:07:20

The overall purpose of constructing a model of human cognition and action such as the Human Model Processor is to approximately predict gross human behavior. Card described the human mind similar to a computer information processing system, and therefore, it should be possible to predict the outcome/timing/behaviors of human responses. This model is useful for the design of user interfaces because it predicts, through calculations, thinking time, memory period, reaction time, which helps programmers to come up with reasonable UI that follows the human actions.

Limitation of the Model Human Processor is that it provides a reasonable approximation that fits majority of users. While it should be a good approximation for a standard case, I don’t think it accurately take into account the behaviors of some modern Human Computer Interaction, for example, users are often not only focusing on 1 task, there are so many environmental factors that distracts users from performing like in the standard calculations.

Dennis Li - 2/20/2013 14:08:53

1) The purpose of constructing the model is to mimic human behavior. By using a model, designers are able to think about how a person would interact with the interface. The feedback given from the model would rate the usability of potential features. For example, the human model gives us an idea of latency between seeing perceiving and reacting. If testing with the model yielded large latency times between seeing onscreen data and the next user input, it may lead the designers to consider a different implementation approach for a certain feature. An example of user latency being a problem is a countdown message. If a user is expected to read a message and make a decisions before the countdown finishes, the human model would allow the designers to more accurately estimate the countdown time needed. Also if too much latency would cause an interface to become annoying to use, this would also be a problem that the designers would have to address.

2) The limits of the Model Human Processor are mainly variations between individual humans. For example, the typing speed of two different people would cause a text entry intensive interface to be appropriate for some people, but difficult to use for slow typers. People with different backgrounds, and knowledge would also be difficult to gauge with the model. If an interface asked users to multiply two numbers to verify that they are human when making an account, this task may be difficult for the arithmetically challenged. The model also fails to take into account different input, perhaps more intuitive input types. For example, how would we take into account accents when applying the model for a natural language processing system like Siri. How would we gauge the difference between shaking and a user on a train with an app that uses an accelerometer?

Sangyoon Park - 2/20/2013 14:09:48

1) The main purpose of Human Model Processor(HMP) is that in a interface design, it is possible to create some functionalities that work better at practical use when the time to perform a certain task for a user is reduced, and this 'time' can be calculated by the Human Model Processor. HMP can be used for creating a human-machine interface where human can perform in the fastest way (similar to the keyboard development - the 'qwerty' keyboard, 'abcde' one, Dvorak, and etc). 2) Although HMP is providing the limits of what we could do for a simple task, it doesn't really give us a big idea about how we could calculate when we are dealing with complex problems. What if an application requires us to think for a long time; it may requires us to reach long-term memory for more than one subject (i.e., some kind of hard puzzle), it could be extremely hard to calculate total time for the task.

Timothy Ko - 2/20/2013 14:10:38

The overall purpose of constructing the Human Model Processor is to be able to accurately predict the amount of time it takes for users to complete certain actions. This can be useful when considering how to design the layout of your user interface.

An example would be where to place buttons in relation to one another based on the Human Model Processor. Another example would be calculating the tradeoffs when you have to decide between putting different items, like buttons or text fields, in the same spot. It may be that putting a text field in between a question and a button would be better because while writing in the text field, the user concurrently processes the decision of what button to press.

From what I have read, the Model Human Processor is limited by the fact that it treats humans like machines. While it does take into account decreased time for increased practice, it doesn’t take into account increased time due to various factors, like boredom or long periods of nonuse.

For example, if a submission form is long enough, and particularly if it requires a number of page changes, actions could take longer than usual due to exhaustion, when alone each of these actions would take as long as would be calculated by the Model Human Processor. What’s worse is if a user gets distracted, which would throw of the model completely.

Christine Loh - 2/20/2013 14:12:26

1) The overall purpose of constructing a model of human cognition and action such as the Human Model Processor is for an information-processing system at the systems level, versus the component level -- we can make predictions of gross human behavior, to help us remember facts and predict user-computer interaction.

2) Some limits of the Model Human Processor are that it is limited to the three interacting subsystems -- the perceptual system, the motor system, and the cognitive system. It's also limited to certain parameters, i.e. the storage capacity in items, the decay time of an item, the main code type, and the cycle time. It fails to capture aspects outside of perception, motor, and cognition when interacting with computer applications, and a more logical sense of interaction rather than interaction with a heavy human bias.

Harry Zhu - 2/20/2013 14:12:34

1) The overall purpose of constructing a model of human cognition/action is to quantify humans in such a way that makes it easier to reason about and to time human reactions. It's much easier to think of human cognition in terms of components. The model can be used to make design decisions much easier, since the all of the timing of the human interactions can be calculated using the equations/timing estimates

2) One limit of the Model Human Processor is that every human is unique, which means that the timings of every person can not be calculated with pinpoint accuracy. There is a lot of noise involved with these calculations. It only focuses on visual and audio aspects of the perceptual model. It doesn't think about touch aspects, which some devices today definitely use, such as rumble feedback in gaming controllers.

Oulun Zhao - 2/20/2013 14:14:37

1. The overall purpose of constructing a model of human cognition and action such as the Human Model Processor is to have a useful tool to evaluate the user interface designs in an early stage as well as to predict different performance for different design alternatives. Human Model Processor is useful because it allows a UI designer to predict the performance of the interface with respect to time it takes a person to complete a task without performing user experiments

2. Although HMP is very useful, it has its own limits and fails to capture following two factors: a. The effects of the environment. For example: a person using the interface in a quite and comfortable room will be different from using that on a noisy street. b. The effects of multitasking. For example: a person might be using the interface while listening to music or talking on the phone. This will effect the reaction time.

Brian Wong - 2/20/2013 14:18:57

1) A Human Model Processor provides a very scientific, standard, and absolute way of measuring response times in user interfaces. Based on empirical evidence, the Human Model Processor can be used by all designers without worry of subjectivism. There are clear and standard values that are used, and ranges are always employed, so that one can know, objectively, the response one could expect from a particular user interface. Specifically, it is useful for measuring the response time of subjects based on the placement of objects such as buttons, reading input that requires time to process, as well as the idea of if your app is forcing people to use working memory to remember things short term.

2) The Model Human Processor is heavily based on measuring response times based off of the time of visual or auditory stimuli to be processed cognitively and reacted upon physically. It does not have subjective ways of measuring things such if a design is 'pretty', 'modern', 'simple', etc. The MHP may show that the placement of these three buttons, based on their usage, is best in this particular arrangement. However, only a user can tell you if that arrangement is easy to remember or if it is appealing to the eye.

Tananun Songdechakraiwut - 2/20/2013 14:24:49

1) Overall purpose: It is a way to evaluate the usability of an application. Since it is a human cognitive modeling method that used to calculate the time to perform a certain kind of task(to approximate human behavior), it can potentially be used by a designer to predict the human performance (with respect to time, no performing experiment). It is a way to reason why one interface is a better design than another and thus the designer is able to predict what types of interface features work well and make the interface that fits perfectly the way a user does tasks.

Useful for design UI: 1. It gives a system designer more heuristics for design 2. Can think of it as a rational, scientific ways to defend design ideas and prove design decisions to folks like marketing, engineer. 3. Allows the designer to easily determine how design decisions impact time on a task. 4. Can be used to predict and compare usability of various interface designs such as learnability, error rate, and task performance. 5. Used to develop

2) Limit: humans are limited in their capabilities to cope with task. This might result from memory as the limiting agent, or processing. There are notion stating that each of the two may be limiting but in different parts of performance- processing position, parallel system, serial system.

The modeling method fails to capture: - Any emotional qualities(is the user frustrated to use the system?, is the user interface ugly?, does the user feel sleepy while using?, is it remeberable?) - It won't tell us about user's goals - Any ergonomic qualities(Is it easy to read?, is icon recognizable?, good branding?)

Alysha Jivani - 2/20/2013 14:28:20

(1) Constructing a model of human cognition and action (such as the Human Model Processor) seems to serve the purpose of quantifying and better understanding how human users perceive and interact with their environment, so that we can improve design to better fit human needs. Such a model can be useful in designing user interfaces because it can inform the designers about the abilities and limitations of a human. For example, understanding how the visual system works (like the phenomenon of visual persistence – here, described as the “visual image store”) and how many stimuli a user can perceive and actually retain in a given amount of time is useful when designing user interfaces. It can inform the designer about what kind of sensory and perception thresholds need to be met by the design, as well as what the upper bounds for human senses, attention, and working memory are. These, in turn, can impact the user’s ability to discern between options and the speed at which they view, select, and click on certain buttons, etc.

(2) One limit that I noticed regarding the Model Human Processor is that, right at the start, it describes the various components of the brain/mind as being separate processors. While it helps to simplify and perhaps localize/attribute specific cognitive processes, there is always the issue that the brain functions as a whole, and that many processes tend to interact with one another. It is possible (and maybe even probable) that, by reducing the brain to these separate processors, we could lose our understanding of the bigger picture (the gestalt) and intricacies that develop as a result of the brain processing as a whole. In terms of interacting with computer applications, I think it might be leaving out some of the important issues of *how* a human learns (even though it addresses the Power Law of Practice) and maybe some of the more heuristic approaches that a person uses while interacting with an application.

Samir Makhani - 2/20/2013 14:29:55

1.) The overall purpose of constructing models like the Human Model Process is so that we can understand, predict, and simulate user performance that is relevant to human-computer interaction. There are many ways that a model like that can be useful for designing user interfaces. The values of the parameters from memories and processors, such as the processor cycle time, memory capacity, memory decay rate, and the cycle time, provide us much detail while investigating how great the design a user interface is. One direct example is the decay rate. What if there was a user-interface that had so many buttons, and pictures, with different functionality, that each time the user returned back to the interface, there would be a steep learning curve to remember or even re-learn the functionality of the interface? Within the cognitive system, we can evaluate and determine an interface where we can provide an interface where users can use their Long-Term memory to store knowledge for future use. If the interface is simple enough, and the buttons have images that make it very intuitive what their functionality is, then when the user returns to the product at a later time, they will not have to spend that annoying catch-up time to re-recognize the interface. We can iterate on the simplicity of the interface by using the Model Human Processor. Let's say I've constructed a new photoshop application, that allows users to create graphics. Each time the user returns to the interface, we can do studies to see how long it takes them to recognize the interface and immediately get started on creating graphics. If the time spent(decay time) is very high, then clearly there is something wrong with our interface, and it needs to be simpler. We can fix this by getting feedback from the users, and using these quantifiable variables, such as decay time, to determine the quality status of our user interface. The same applies for the remainder of the parameters - we can use these to our advantage and iterate on users to create a better design of user interfaces.

2.) One of the limits described in the articles is that this model does not "do justice to the richness and subtlety of the human mind." I think this means that it does not better the human mind, however, it allows us to calculate human performance relevant to HCI interaction. Thus, the limit of the Model Human Processor is that it will not improve the human mind, but only provide tools that help us understand it.

Some aspects of interacting with computer applications that it fails to capture is visual appearance. What if a user doesn't want to interact with an interface because it's not visually appealing, and the colors are so bright that it's hard on their eyes? How can we use the parameters given to determine whether the problem of the interface is because the visual appearance is unfavorable to the user's likings? In a bigger picture, how can we evaluate/integrate user's taste based on these parameters? Many users come from different backgrounds, and may have their own cultural parameters that may limit their decay rate, or other parameters provided by the Model Human Processor. If I visit a page in a different language, chances are I will not be able to remember majority of it a later time.

Minhaj Khan - 2/20/2013 14:34:58

Constructing a model for human cognition allows a Ui designer to design according to a robust and methodical construct of how a human would act and perceive a UI interface. One way such a model can be useful is by assessing how a human would interpret the size and distance of different Ui elements and fonts. Greater distance implies no connectivity for example, and a model for human cognition would take these elements into account when designing Ui.

A limitation of the human model processor is that it may not capture all the intricacies of human computer interaction. One example would be that the model may perceive certain UI elements to be connected the way it's perception algorithm is coded, but in the same circumstance an average human may not find the same elements to be connected and may per dive it differently because perception is subjective and can't entirely be captured through algorithms