Human processor model

Key takeaways

Human processor model belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Human processor model to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Human processor model from memory before moving on to harder problems.

Reference excerpt

Human processor model or MHP (Model Human Processor) is a cognitive modeling method developed by Stuart K. Card, Thomas P. Moran, & Allen Newell (1983) used to calculate how long it takes to perform a certain task. Other cognitive modeling methods include parallel design, GOMS, and keystroke-level model (KLM).

Cognitive modeling is one way to evaluate the usability of a product. This method uses experimental times to calculate cognitive and motor processing time. The value of the human processor model is that it allows a system designer to predict the performance with respect to time it takes a person to complete a task without performing experiments. Other modeling methods include inspection methods, inquiry methods, prototyping methods, and testing methods. The standard definition for MHP is: The MHP draws an analogy between the processing and storage areas of a computer, with the perceptual, motor, cognitive and memory areas of the computer user. The human processor model uses the cognitive, perceptual, and motor processors along with the visual image, working memory, and long term memory storages. A diagram is shown below. Each processor has a cycle time and each memory has a decay time. These values are also included below. By following the connections diagrammed below, along with the associated cycle or decay times, the time it takes a user to perform a certain task can be calculated. Studies into this field were initially done by Stuart K. Card, Thomas P. Moran, & Allen Newell in 1983. Current studies in the field include work to distinguish process times in older adults by Tiffany Jastrembski and Neil Charness (2007

How to calculate The calculations depend on the ability to break down every step of a task into the basic process level. The more detailed the analysis, the more accurate the model will be to predict human performance. The method for determining processes can be broken down into the following steps.

Write out main steps based on: a working prototype, simulation, step by step walk-through of all steps Clearly identify the specific task and method to accomplish that task For each final step identify sub-levels down to a basic process (in the diagram or chart below) Convert into pseudo code (writing out methods for each step) List all assumptions (will be helpful as multiple iterations are completed) Determine time of each operation (based on the table below) Determine if operation times should be adjusted (slower for elderly, disability, unfamiliarity, etc.) Sum up execution times Iterate as needed and check with prototyping if possible

Potential uses Once complete, the calculations can then be used to determine the probability of a user remembering an item that may have been encountered in the process. The following formula can be used to find the probability: P = e-K*t where K is the decay constant for the respective memory in question (working or long term) and t is the amount of time elapsed (with units corresponding to that of K). The probability could then be used to determine whether or not a user would be likely to recall an important piece of information they were presented with while doing an activity. It is important to deduce beforehand whether the user would be able to repeat the vital information throughout time t, as this has a negative impact on the working memory if they cannot. For example, if a user is reading lines of text and is presented with an important phone number in that text, they may not be able to repeat the number if they have to continue to read. This would cause the user’s working memory’s decay time to be smaller, thus reducing their probability of recall.

See also Working memory GOMS KLM (human-computer interaction) Human reliability

References Card, S.K; Moran, T. P; and Newell, A. The Model Human Processor: An Engineering Model of Human Performance. In K. R. Boff, L. Kaufman, & J. P. Thomas (Eds.), Handbook of Perception and Human Performance. Vol. 2: Cognitive Processes and Performance, 1986, pages 1–35. Liu, Yili; Feyen, Robert; and Tsimhoni, Omer. Queueing Network-Model Human Processor(QN-MHP): A Computational Architecture for Multitask Performance in Human-Machine Systems. ACM Transactions on Computer-Human Interaction. Volume 13, Number 1, March 2006, pages 37-70. Jastrzembski, Tiffany; and Charness, Neil. The Model Human Processor and the Older Adult: Parameter Estimation and Validation within a Mobile Phone Task. Journal of Experimental Psychology: Applied. Volume 13, Number 4, 2007, pages 224-248. Specific

Worked examples

Example 1 — a first encounter with Human processor model

Start with the simplest possible case. Write down what Human processor model claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Human processor model before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Human processor model ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Human processor model

In research: Human processor model appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Human processor model in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Human processor model is common in secondary-school and first-year university syllabi. It links to neighbouring topics Human–computer interaction, so understanding it makes those chapters shorter.
In everyday life: Look for Human processor model outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

How to study Human processor model in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Human processor model means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Human processor model out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Human processor model in simple terms?

Human processor model or MHP (Model Human Processor) is a cognitive modeling method developed by Stuart K. Card, Thomas P.

Why does Human processor model matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Human processor model?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Human processor model.