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Cognitive Modeling

GOMS, Keystroke Model

Getting some details right!

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Cognitive Modeling

• Detailed

• Time consuming

• Surprisingly accurate

• Currently for– what will a user do ideally

– what mental and physical capacities will a system require

– how long will it take to perform

– how long will it take to learn

– for skilled tasks

– not for initial exploration of “walk up and use” systems

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GOALS

Intention Evaluation

InterpretationAction Specification

PerceptionExecution

PerceptionSaccadePerceive

COGNITIONExecute a mental step

Choose among methods

MEMORYRetrieve unit

from LTM

STM:Keep track of where you are

MOTOR MOVEMENTSKeystroke

PointMove hands

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Two parts

• GOMS– This is in memory, it’s what you know when you use a piece of

software

– GOMS is the knowledge base

– The stored information that drives behavior

• The Model Human Processor – is the engine that operates on this knowledge

– It selects the next thing to do from this knowledge base

» Unpack a goal into subgoals, keep those in memory

» Select the next subgoal, find the right method, store that

» Find the set of actions for that method

» Elicit those actions

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GOMS

• What the user has to know – a task analysis of external and internal

actions for a particular piece of software

–GOMS

»Goals

»Operators

»Methods

»Selection Rules

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GOMS

• Goal–High level goal, e.g., make the slide show with

blue background and white letters

• Methods–Various ways of doing things, e.g., Choose

color scheme or Background

• Selection Rules– When to use which method, e.g. depending on how

much you want to change.

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GOMS

• Operators–Actions both mental and physical

–Methods are made up of operators

–E.g., Move hand to mouse, move mouse such that pointer is on menu item, push mouse button down, move mouse to exact item, release mouse button.

–E.g., Retrieve the sub-goal of making a the background blue, retrieve the sub-goal of making the letters white

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Model Human Processor

• The engine that takes the current task situation

• Uses GOMS knowledge

• Produces action– Unpacking goals and subgoals

– Putting things on STM

– Taking things out of STM to retrieve more in LTM

– Finding Methods

– Enacting the operators

– Realizing that part is done…go get the next goal from STM

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GOMS Analysis: How to do it

• Determine core tasks– Determine component Goals and Subgoals

– Determine Alternative Methods for accomplishing those goals and the Selection Rules

– Determine what Operators are in each Method

• Run the MHP with some specifics about the task– Goals are decomposed into constituents through LTM

lookup

– Choices are determined according to specifics of the situation

– “various goal-method-operator acts take time

» learning times can be calculated by how many steps are new

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What it looks like

Goal: Change the color of the background of all slides to be blue

Step 1. Remember that the slides have to be blueStep 2. Remember that this applies to all slidesStep 3. Selection Rule: If changing a lot of features

(background and text color) use method AOtherwise, use method B.

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Methods made up of OperatorsMethod A:

Step 1. Move mouse to FORMATStep 2. Click on FORMATStep 3. Move mouse down the menu to SLIDE COLOR SCHEMEStep 4. Click on SLIDE COLOR SCHEMEStep 5. Check to see if CUSTOM is the view

If not, move mouse to CUSTOM Click on CUSTOM

Step 6. Recall that the background should be blueStep 7. Find the background blockStep 8. Check to see if the background block is highlighted

if not, Move mouse to background block Click on background block

Step 9. Move mouse to “Change Color”Step 10. Click on “Change Color”Step 11. Find the color closest to “Blue”Step 12. Move mouse to that colorStep 13. Click on that colorStep 14. Move the mouse to “OK”Step 15. Click on “OK”

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Methods made up of Operators

Step 16. Recall that it is to be applied to allStep 17. Move the mouse to APPLY TO ALLStep 18. Click on APPLY TO ALLStep 19. Confirm that it changed.

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Methods made up of OperatorsMethod B

Step 1. Move mouse to FORMATStep 2. Click on FORMATStep 3. Move the mouse to BACKGROUNDStep 4. Click on BACKGROUNDStep 5. Move mouse to the color patchStep 6. Click on the color patchStep 7. Recall that the background should be blueStep 8. Look to see if blue is one of the displayed colorsStep 9a. Move the mouse to the color blueStep 10a. Click on blue

IF NOT, Step 9b Move mouse to MORE COLORSStep 10b. Click on MORE COLORSStep 11b. Check to see if tab STANDARD is front

IF NOT, Step 11c Move mouse to STANDARD Step 11d Click on STANDARD

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Methods made up of Operators

Step 12b. Find the patch closest to blueStep 13b. Click on that patchStep 14b. Move mouse to OKStep 15b. Click on OK

Step 16. Recall that this applies to all slidesStep 17. Move mouse to APLLY TO ALLStep 18. Click on APPLY TO ALLStep 19. Confirm that the change happened

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Using GOMS in design

• How much has to be recalled?– Takes time to learn– Needs to be recalled

• How much is led by recognition? Looking for things– Is the flow easy (e.g., top down, near each other)?

• Are there steps that are unnecessary?– Do menus have to be opened that are extra (I.e., could more be

put on the same dialog box)?

• Are there new methods that could be developed for common tasks?– How often do people use each of the methods?– Is there a way to streamline into shortcuts?

• Is there too much that has to be kept track of?

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Keystroke Level Model

• Look only at the timing of the execution of a task

• There are known parameters– Retrieval of things from Long Term Memory

– Storage and retrieval from Short Term Memory

» literally putting things in and taking them out of STM

» Push, pop from a stack

– Movement of eyes, perceptual acts

– Movement of hands to a place

– Other cognitive acts

» Selecting from various choices

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Keystroke Level Analysis:

How to do it• Determine core tasks

• Determine how to do those tasks on the system being designed or tested– Steps (of the preferred method)

– Requirements both mental and physical

– Look-up on a table the component times

– Add up times

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Table of motor times

• Enter a keystroke 230 msec

• Simple mouse click 80 msec

• Point with a mouse 1500 msec

• Move hands 290 msec

• Eye movement 230 msec

• Reading – If you don’t know what you’re reading 170 msec/syllable

– If you do 130 msec/syllable

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Table of cognitive times

• Eye movement 230 msec

• Perceive 100 msec

• Choose among methods 1250 msec

• Retrieve from memory 1600 msecincludes recognize, confirm

• Learn a name 7 sec/chunk

• Learn method 17 sec/step

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Methods made up of OperatorsMethod A:

Step 1. Move mouse to FORMATStep 2. Click on FORMATStep 3. Move mouse down the menu to SLIDE COLOR SCHEMEStep 4. Click on SLIDE COLOR SCHEMEStep 5. Check to see if CUSTOM is the view

If not, move mouse to CUSTOM Click on CUSTOM

Step 6. Recall that the background should be blueStep 7. Find the background blockStep 8. Check to see if the background block is highlighted

if not, Move mouse to background block Click on background block

Step 9. Move mouse to “Change Color”Step 10. Click on “Change Color”Step 11. Find the color closest to “Blue”Step 12. Move mouse to that colorStep 13. Click on that colorStep 14. Move the mouse to “OK”Step 15. Click on “OK”

1500 801500 80 3301500 801600 330 3301500 801500 80 3301500 801500 80

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Methods made up of Operators

Step 16. Recall that it is to be applied to allStep 17. Move the mouse to APPLY TO ALLStep 18. Click on APPLY TO ALLStep 19. Confirm that it changed.

16001500 801600

3x1600 + 6x1500 + 6x80 +4x330 = 15,600 msec = 15.6 sec

2x1500 + 2x80 = 3,160 msec = 3.2 sec 15.6 + 3.2 = 18.8 sec.

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Methods made up of OperatorsMethod B

Step 1. Move mouse to FORMATStep 2. Click on FORMATStep 3. Move the mouse to BACKGROUNDStep 4. Click on BACKGROUNDStep 5. Move mouse to the color patchStep 6. Click on the color patchStep 7. Recall that the background should be blueStep 8. Look to see if blue is one of the displayed colorsStep 9a. Move the mouse to the color blueStep 10a. Click on blue

IF NOT, Step 9b Move mouse to MORE COLORSStep 10b. Click on MORE COLORSStep 11b. Check to see if tab STANDARD is front

IF NOT, Step 11c Move mouse to STANDARD Step 11d Click on STANDARD

1500 801500 801500 801600 3301500 80

1500 80 3301500 80

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Methods made up of Operators

Step 12b. Find the patch closest to blueStep 13b. Move the mouse to that patchStep 14b. Click on that patchStep 15b. Move mouse to OKStep 16b. Click on OK

Step 17. Recall that this applies to all slidesStep 18. Move mouse to APLLY TO ALLStep 19. Click on APPLY TO ALLStep 20. Confirm that the change happened

3301500 801500 80

16001500 801600

3x1600 + 5x1580 = 12,700msec = 12.7 sec

4x1580 + 2x330 = 6,980 msec. = 6.9 sec 12.7 + 6.9 = 19.7 sec!

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Exercise 1

• If there are 20 changes to make in words in a paragraph of 15 lines long, should I find and edit each one or retype the whole paragraph?

• Retype:

• Find and edit 20 changes:

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Exercise 2

• How long does the system response time have to be (e.g. on my Cable Modem at home which is

really slow for outgoing requests) for the pull down choice-set to appear

before it is shorter to just type in a known url? – E.g. http://coursetools.ummu.umich.edu

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Extensions to the original GOMS models:

• More detailed analysis of times for very skilled, rapid tasks

• Critical Path Analysis of mental/physical acts, with dependencies

• Perceptual, cognitive, motor

• What can be done in parallel, what requires series

• Calculate different paths for different assumed user parameters or task situations

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Success Cases

• Directory Assistance– Key less see more

• Toll and Assistance Operator– New ergonomic keyboard

• Back office deposit reconciliation– Visual display for checks, deposit slips

• Cognitive Orthotics– customized advice on use of mouthstick letter entry

and word guessing strategies