1 Cognitive Modeling GOMS, Keystroke Model Getting some details right!

2 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

3 GOALS IntentionEvaluation Interpretation Action Specification PerceptionExecution Perception Saccade Perceive COGNITION Execute a mental step Choose among methods MEMORY Retrieve unit from LTM STM: Keep track of where you are MOTOR MOVEMENTS Keystroke Point Move hands

4 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

5 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

6 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.

7 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

8 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

9 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

10 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 blue Step 2. Remember that this applies to all slides Step 3. Selection Rule: If changing a lot of features (background and text color) use method A Otherwise, use method B.

11 Methods made up of Operators Method A: Step 1. Move mouse to FORMAT Step 2. Click on FORMAT Step 3. Move mouse down the menu to SLIDE COLOR SCHEME Step 4. Click on SLIDE COLOR SCHEME Step 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 blue Step 7. Find the background block Step 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 color Step 13. Click on that color Step 14. Move the mouse to “OK” Step 15. Click on “OK”

12 Methods made up of Operators Step 16. Recall that it is to be applied to all Step 17. Move the mouse to APPLY TO ALL Step 18. Click on APPLY TO ALL Step 19. Confirm that it changed.

13 Methods made up of Operators Method B Step 1. Move mouse to FORMAT Step 2. Click on FORMAT Step 3. Move the mouse to BACKGROUND Step 4. Click on BACKGROUND Step 5. Move mouse to the color patch Step 6. Click on the color patch Step 7. Recall that the background should be blue Step 8. Look to see if blue is one of the displayed colors Step 9a. Move the mouse to the color blue Step 10a. Click on blue IF NOT, Step 9b Move mouse to MORE COLORS Step 10b. Click on MORE COLORS Step 11b. Check to see if tab STANDARD is front IF NOT, Step 11c Move mouse to STANDARD Step 11d Click on STANDARD

14 Methods made up of Operators Step 12b. Find the patch closest to blue Step 13b. Click on that patch Step 14b. Move mouse to OK Step 15b. Click on OK Step 16. Recall that this applies to all slides Step 17. Move mouse to APLLY TO ALL Step 18. Click on APPLY TO ALL Step 19. Confirm that the change happened

15 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?

16 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

17 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

18 Table of motor times Enter a keystroke230 msec Simple mouse click 80 msec Point with a mouse1500 msec Move hands290 msec Eye movement230 msec Reading –If you don’t know what you’re reading 170 msec/syllable –If you do 130 msec/syllable

19 Table of cognitive times Eye movement230 msec Perceive100 msec Choose among methods1250 msec Retrieve from memory1600 msec includes recognize, confirm Learn a name7 sec/chunk Learn method17 sec/step

20 Methods made up of Operators Method A: Step 1. Move mouse to FORMAT Step 2. Click on FORMAT Step 3. Move mouse down the menu to SLIDE COLOR SCHEME Step 4. Click on SLIDE COLOR SCHEME Step 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 blue Step 7. Find the background block Step 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 color Step 13. Click on that color Step 14. Move the mouse to “OK” Step 15. Click on “OK”

21 Methods made up of Operators Step 16. Recall that it is to be applied to all Step 17. Move the mouse to APPLY TO ALL Step 18. Click on APPLY TO ALL Step 19. Confirm that it changed x x x80 +4x330 = 15,600 msec = 15.6 sec 2x x80 = 3,160 msec = 3.2 sec = 18.8 sec.

22 Methods made up of Operators Method B Step 1. Move mouse to FORMAT Step 2. Click on FORMAT Step 3. Move the mouse to BACKGROUND Step 4. Click on BACKGROUND Step 5. Move mouse to the color patch Step 6. Click on the color patch Step 7. Recall that the background should be blue Step 8. Look to see if blue is one of the displayed colors Step 9a. Move the mouse to the color blue Step 10a. Click on blue IF NOT, Step 9b Move mouse to MORE COLORS Step 10b. Click on MORE COLORS Step 11b. Check to see if tab STANDARD is front IF NOT, Step 11c Move mouse to STANDARD Step 11d Click on STANDARD

23 Methods made up of Operators Step 12b. Find the patch closest to blue Step 13b. Move the mouse to that patch Step 14b. Click on that patch Step 15b. Move mouse to OK Step 16b. Click on OK Step 17. Recall that this applies to all slides Step 18. Move mouse to APLLY TO ALL Step 19. Click on APPLY TO ALL Step 20. Confirm that the change happened x x1580 = 12,700msec = 12.7 sec 4x x330 = 6,980 msec. = 6.9 sec = 19.7 sec!

24 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:

25 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.

26 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

27 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