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Synthesizing Frameworks, Part 1: The Model Human Processor, GOMS, and KLM
Mark W. Newman SI 688 Fall 2010
Synthesizing Frameworks
How to make all this scien=fic knowledge about human percep=on, cogni=on, motor performance useful for design?
Go beyond guidelines, heuris=cs, best prac=ces
Two examples: Card, Moran, and Newell’s “applied psychology”
Models and methods and to predict human-‐system interac=on performance
Green, Petre, and Blackwell’s “cogni=ve dimensions” A “sensi=zing framework” to guide discussion about design tradeoffs
Synthesizing Frameworks
How to make all this scien=fic knowledge about human percep=on, cogni=on, motor performance useful for design?
Go beyond guidelines, heuris=cs, best prac=ces
Two examples: Card, Moran, and Newell’s “applied psychology”
Models and methods and to predict human-‐system interac=on performance
Green, Petre, and Blackwell’s “cogni=ve dimensions” A “sensi=zing framework” to guide discussion about design tradeoffs
Today
Next Week
A Watershed Moment
Card, Moran, Newell 1983 Synthesized large volumes
of findings from Cog. Psych. to date
Ini=ated call for an “applied psychology”
Ar=culate a compelling research agenda for HCI that helped organize the field
Underpinnings: Information Processing
Prior to CMN
Informa=on Processing was used To describe human cogni=on
To debunk behaviorism
As a framework for par==oning and organizing research
Informa=on Processing was not used To inform systems design
Goals of CMN “A scien=fic psychology should not only help us to understand our
own human nature, it should help us in our prac=cal affairs.”
“A scien=fic psychology should help us in arranging this interface so it is easy, efficient, error-‐free——even enjoyable.”
“knowledge of human cogni=ve behavior is sufficiently advanced to enable its applica=ons in computer science and other prac=cal domains.”
“Our own goal is to help create … an applied informa=on-‐processing psychology.”
“Applying psychology to the evalua=on of systems is assuredly easier than applying it to the design of systems.”
From Ch. 1, Psych of HCI
CMN’s Core Concepts
Model Human Processor: a simplified model of human informa=on processing that can be used by designers
GOMS: a method for represen=ng people’s task-‐based interac=on with systems that supports detailed analysis
The Keystroke-‐Level Model: a quan=ta=ve technique for predic=ng performance on specific interac=ve tasks
Model Human Processor
Model Human Processor
Four types of memory Differ in terms of capacity,
decay =me, encoding
Three processors Differ in terms of
processing =me (and func=on)
Operate serially, though can be pipelined
MHP: Principles of Operation Recognize-‐Act Cycle
Interac=on b/t WM & LTM
Variable Perceptual Rate Speed varies with input
intensity
Encoding Specificity Informa=on is encoded
before stored
Discrimina=on Retrieval is determined by
available candidates + cues
Variable Cogni=ve Rate Cycle faster when demand is
higher
MHP: Principles of Operation
Fijs’ Law
Power Law of Prac=ce Performance increases
with prac=ce (with log(t))
Uncertainty Principle (Hick-‐Hyman Law)
Ra=onality Principle Goals + Task + Operators +
Inputs + Knowledge + Process-‐limits -‐> Behavior
Problem Space Principle Ra=onality described via
States of knowledge Operators to change state Constraints on operators Rules for selec=ng
operators
Is This How Humans Work?
Only if you squint
An admijed simplifica=on “All models are wrong, some models are useful.” – G. E. P. Box
Goals of MHP: Ability to calculate parameters on human performance from the
analysis of the task
Giving the [designer] knowledge in a form rela=vely easy to assimilate
…Are we there yet?
Decision Making
Decision Making
Decision Making
Decision Making
Perceptual Processor samples visual field
Decision Making
Perceptual Processor stores image in visual image store
Decision Making
Perceptual Processor encodes input and stores in STM
Decision Making
Cogni=ve Processor samples working memory
Decision Making
Cogni=ve Processor associates symbol with task stored in LTM, task info moved to STM.
Decision Making
Cogni=ve Processor directs Motor Processor to move eyes, scan bujons
Decision Making
Perceptual Processor receives input: bujon has been seen.
Decision Making
Visual Image Store -‐> Encoding -‐> Working Memory
Decision Making
Cogni=ve Processor “reads” working memory, compares bujon to s=mulus
Decision Making
Cogni=ve Processor directs Motor Processor to move finger and push
What Good is the MHP?
If you can es=mate the =me for each stage, you can predict performance
S=ll very difficult to use Tedious for even a small example
Great deal of knowledge required
Lots of room for (mis-‐) interpreta=on
Making the MHP (More) Useful: GOMS
Goals of MHP: Ability to calculate parameters on human performance from the
analysis of the task
Giving the [designer] knowledge in a form rela=vely easy to assimilate
GOMS: a method of task representa=on that affords analysis via the MHP (sort of)
GOMS
Goals Goal that the user is trying to accomplish—these can be
decomposed into subgoals
Operators Individual, low-‐level ac=ons performed using the system
Methods Sequences of Operators used to accomplish Goals
Selec=on Rules Criteria to decide when to use different Methods
From B. E. John. Informa=on Processing and Skilled Behavior. In J. M. Carroll, ed. HCI Models, Theories, and Frameworks. 2003.
Example GOMS model for “MOVE-TEXT” in MS Word
Example Operators in GOMS
Operators Physical
Move hand to mouse Move mouse such that pointer is on menu =tle Push mouse bujon down Move mouse to exact item Release mouse bujon
Mental Retrieve the sub-‐goal of cuqng text Recall that “Edit” menu is where “Cut”
command is found Verify feedback
GOMS vs. MHP
?
The Keystroke-‐Level Model
A method for predic=ng performance given a GOMS model
A set of guidelines for choosing opera=ons and defining methods
A simplified set of calcula=ons based on the MHP
Limited to predic=ng the (expert) execu/on /me of unit tasks No method selec=on
No learning, exploring, errors
No decision making about goal decomposi=on
KLM’s 6 7 Operators
K : keystroking
P : poin=ng (moving the mouse to a target)
B: pressing or releasing mouse bujon*
H : homing (moving hand from keyboard to mouse)
D : drawing (drawing lines in segments)
M : mental work (retrieving from memory, verifying feedback)
R: system response
*: Added by Kieras, D. (1993, 2001), Using the Keystroke-‐Level Model to Es=mate Execu=on Times
Timing
K B P H D
M R
Keystroking Press button on mouse Point Home (Move hand to/from keyboard/mouse) Draw lines (domain dependent)
Mentally prepare (access LTM) System Response
0.28 (.12-1.2) 0.1* 1.1 0.4 -
1.2* -
Operator Description Time (s)
* Times from Kieras, D. (1993, 2001), Using the Keystroke-‐Level Model to Es=mate Execu=on Times
An Example
An Example (Physical Only)
1. point to file icon (P) 2. press and hold mouse
bujon (B) 3. drag file icon to trash can
icon (P) 4. release mouse bujon (B) 5. point to original window (P)
Total =me = 3P + 2B = 3*1.1 + 2*.1 = 3.5 sec
1. point to file icon (P) 2. click mouse bujon (BB) 3. point to file menu (P) 4. press and hold mouse bujon
(B) 5. point to DELETE item (P) 6. release mouse bujon (B) 7. point to original window (P)
Total =me = 4P + 4B = 4*1.1 + 4*.1 = 4.8 sec
Power Key Method (Physical Only)
1. point to file icon (P) 2. click mouse bujon (BB) 3. move hand to keyboard (H) 4. hit command key command-‐T (KK) 5. move hand back to mouse (H)
Total =me = P + 2B + 2H + 2K = 1.1 + .2 + .8 + .56 = 2.66 sec
Drag to Trash: Going Mental ini=ate the dele=on (decide to do the task) (M) find the file icon (M) point to file icon (P) press and hold mouse bujon (B) verify that the icon is reverse-‐video (M) find the trash can icon (M) drag file icon to trash can icon (P) verify that the trash can icon is reverse-‐video (M) release mouse bujon (B) verify that the trash can icon is bulging (M) find the original window (M) point to original window (P)
Total =me = 3P + 2B + 7M = 11.9 sec
Where to Place the M’s
Ini=a=ng a task
Making a strategy decision
Retrieving a chunk from memory
Finding something on the screen
Thinking of a task parameter
Verifying that a specifica=on or ac=on is correct
* Times from Kieras, D. (1993, 2001), Using the Keystroke-‐Level Model to Es=mate Execu=on Times
Experts and M…
ini=ate the dele=on (decide to do the task) (M)
find the file icon (M) point to file icon (P) press and hold mouse bujon (B) verify that the icon is reverse-‐video (M) find the trash can icon (M) drag file icon to trash can icon (P) verify that the trash can icon is reverse-‐
video (M) release mouse bujon (B) verify that the trash can icon is bulging
(M) find the original window (M) point to original window (P)
Total =me = 3P + 2B + 2M = 5.9 sec
ini=ate the dele=on (decide to do the task) (M)
find the file icon (M) point to file icon (P) press and hold mouse bujon (B) verify that the icon is reverse-‐video (M) find the trash can icon (M) drag file icon to trash can icon (P) verify that the trash can icon is reverse-‐
video (M) release mouse bujon (B) verify that the trash can icon is bulging
(M) find the original window (M) point to original window (P)
Total =me = 3P + 2B + 7M = 11.9 sec
If there are 20 (one character) changes to make in words in a paragraph of 8lines long, should I find and edit each one or retype the whole paragraph? (assume 80 char/line)
Exercises
Key press= 0.28 Button=0.1
Pointer move=1.1 Hand move=0.4
Mental effort=1.2 System Response=???
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?
Key press= 0.28
Button=0.1
Pointer move=1.1
Hand move=0.4
Mental effort=1.2
Approach #1: Delete whole paragraph & retype Step 1: Delete Paragraph M Recall that text must be selected & deleted 1.2 P Move cursor to beginning of paragraph 1.1 BB Click 0.1
0.1 P Move cursor to end of paragraph 1.1 KBB Shift-Click 0.28
0.1 0.1
K Type DEL 0.28 H Move Hand to Keyboard 0.4 MPBBPKBBKH 4.76
Step 2: Retype paragraph K Type (8 * 80=640) characters 0.28 640K 179.2
Approach #1 Total: 183.96
Approach #2: Find and fix 20 characters Subgoal: Find and fix one character M Locate character to delete 1.2 H Move Hand to mouse 0.4 P Move cursor to after character 1.1 BB Click 0.1
0.1 M Recall that delete must be typed 1.2 H Move Hand to keyboard 0.4 K Type DEL 0.2 M Recall that character must be typed 1.2 K Type Char 0.28 MHPBBMHKMK 6.1
Approach #2 Total (20 * MHPBBMHKMK) 123.6
How long does the system response =me have to be for the Google Toolbar Bookmarks pull-‐down menu to appear before it is shorter to just type in a known url (hjp://ctools.umich.edu)? Note: assume no autocomplete
Exercises
Key press= 0.28 Button=0.1
Pointer move=1.1 Hand move=0.4
Mental effort=1.2 System Response=???
How long does the system response =me have to be for the Google Toolbar Bookmarks pull-‐down menu to appear before it is shorter to just type in a known url? e.g. hjp://ctools.umich.edu
Key press= 0.28
Button=0.1
Pointer move=1.1
Hand move=0.4
Mental effort=1.2
System Response=???
Exercise 2
Approach #1: Use Google Bookmarks Menu M Recall CTools is in bookmarks menu 1.2 P Move pointer to bookmarks menu 1.1 B Press 0.1 R Wait for menu items to display R P Move pointer to CTools item 1.1 B Release 0.1 MPBRMPB 3.6+R
Approach #2: Type in URL M Recall need to use address bar 1.2 P Move pointer to address bar 1.1 BBBB Double-click text 0.1
0.1 0.1 0.1
M Recall need to type "http://ctools.umich.edu" 1.2 H Move hand to keyboard 0.4 24K Type "http://ctools.umich.edu" + RTN 6.72 MPBBBBMHK(24) 11.02
R = (11.02-3.6) 7.42
Accuracy of GOMS/KLM
KLM: accurate ± 33%
CMN-‐GOMS: accurate 90% of the =me
CPM-‐GOMS: accurate ± 12%*
* Gray, W. D., John, B. E., and Atwood, M. E. 1993. Project Ernes=ne: valida=ng a GOMS analysis for predic=ng and explaining real-‐world task performance. Hum.-‐Comput. Interact. 8, 3 (Sep. 1993), 237-‐309.
Helping Designers Create Models
hjp://cogtool.hcii.cs.cmu.edu/
Helping Designers Create Models
hjp://cogtool.hcii.cs.cmu.edu/
Review (Whither GOMS?) CMN’s “applied psychology” approach was enormously influen=al in
early growth of HCI Created the possibility of an academic discipline MHP-‐GOMS-‐KLM had impacts within research and prac=ce
Current impact on prac=ce: minimal (mostly) Much Interac=on Design today op=mizes for
learnability, desirability, usefulness, etc. Excep=ons: domains where performance is king
(e.g., fighter cockpit design)
Next week: a completely different approach to synthesizing cogni=on Covers more aspects of usability than expert performance Less predic=ve and direc=ve