1. The Essential Role of Mental Models in HCI: Card, Moran and Newell
Papers:
Kate Ehrlich, Lorin Hochstein

2. Introduction Example Three blind men Query : Visualize a horse?
Attributes and Operations
Horse ( Four legs, people can ride to move from point A to B. Rider has controls to change direction, needs to be fed etc.)

3. Mental Model
An explanation in someone’s thought process for how something works in the real world
Internal symbol or representation of external reality
Mostly Kids
Originated by Kenneth Craik “The nature of Explanation”
Part of Cognition Science

4. Mental Models & HCI
New research based Mental models for computer systems
Interface designer started using Mental Model
Build computers Mental Model
Card, Moran and Newell (1983) – “The Psychology of Human-Computer Interaction”
“Our purpose in this book is to help lay a scientific foundation for an applied psychology concerned with the human users of interactive computer systems. Although modern cognitive psychology contains a wealth of knowledge of human behavior, it is not a simple matter to bring this knowledge to bear on the practical problems of design – to build an applied psychology that include theory, data and methodology.”

5. HCI Metal Model Types
Cognitive Science - Metal Models abstract representation
HCI - More concrete
Types of Models in HCI
The actual Model of the System
The engineer Model of the System
Drives technical design and implementation
UI designer’s model of the System
The user Model of the system

6. GOMS
In HCI - provide a theory of the user’s representation of the system as well as its construction.
According to Card et al - mental model not only be theoretical grounded but also be testable.
They came up with Model - GOMS G O M S
Goals
Operators
Methods
Selection rules

7. GOMS - Goals Goals are what the user is trying to accomplish
Various levels of abstraction,
Very high-level goals (e.g. WRITE-RESEARCH-PAPER)
low-level goals (e.g. DELETE-WORD).
Higher-level goals are decomposable into sub goals, and are arranged hierarchically

8. GOMS - Operators
Operators are the actions that systems let user to perform.
e.g. DOUBLE-CLICK-MOUSE, PRESS-INSERT-KEY, other keyboard commands etc.
Used to accomplish the goals
Atomic elements in the GOMS model.
Operators are not decomposable
Assumption - Operator requires a fixed time
(e.g. CLICK-MOUSE button takes 0.20 seconds to execute).

9. GOMS - Methods Sequence of sub-goals and operators to achieve a goal
For example
Goal - DELETE-WORD
MOVE-MOUSE to the beginning of the word, and PRESS-ALT-D-KEY-COMBINATION (the use-mouse-delete-word method).
Use arrow keys to reach the beginning of the word (the use-arrows-delete-word method).
Algorithm that determines the sequence of sub-goals and operators

10. GOMS – Selection Rules Goals could have multiple methods
Which method should be used?
E.g. instead of using mouse to select the text for deletion, the user could use the keyboard arrows.
Represent the user's knowledge
A conditional statement
"if the word to be deleted is less than 3 lines away from the current cursor location, then use the use-arrows-delete-word-method, else use the use-mouse-delete-word method".

11. Keystroke-Level Model - KLM
Simplified version of GOMS (Card & Moran )
Method to predict user performance
Estimate execution time by listing the sequence operators and then summing the time of individual operator
Aggregates all the perceptual and cognitive function into a single value for entire task, using a heuristic
Does not employ selection rules.
Six Classes of operators
K : Pressing a Key
P : Pointing to a location on screen with mouse.
H : Moving hands to Home position on the keyboard
M : Mentally preparing to perform an action
R : System Response

12. Example - KLM
Consider the text editing task of searching a Microsoft Word document for all occurrences of a four-letter word, and replacing it with another four-letter word
According to this KLM model, it takes 10.2 seconds to accomplish this task

13. Example - KLM Description Operation Time (sec) Total 10.2
Reach for mouse
H [mouse]
0.40
Move pointer to “Replace” button
P [menu item]
1.10
Click on “Replace” command
K [mouse]
0.20
Home on keyboard
H [keyboard]
Specify word to be replaced
M4K [word]
2.15
Point to correct field
P [field]
Click on field
H [Keyboard]
Type new word
Move pointer on Replace-all
P [replace-all]
Total
10.2

14. Example 2 - GOMS This example is taken from John & Kieras (1996).
It models the task of moving text in a Word processor, in the context of editing a manuscript.
Use of sub-goals and selection rules, which do not exist in KLM

15. Example 2 - GOMS GOAL: EDIT-MANUSCRIPT
. GOAL: EDIT-UNIT-TASK ... repeat until no more unit tasks
. . GOAL: ACQUIRE UNIT-TASK
GOAL: GET-NEXT-PAGE ... if at end of manuscript page
GOAL: GET-FROM-MANUSCRIPT
. . GOAL: EXECUTE-UNIT-TASK ... if a unit task was found
GOAL: MODIFY-TEXT
[select: GOAL: MOVE-TEXT* ...if text is to be moved
GOAL: DELETE-PHRASE ...if a phrase is to be deleted
GOAL: INSERT-WORD] ... if a word is to be inserted
VERIFY-EDIT

16. * Expansion of MOVE-TEXT goal
GOAL: MOVE-TEXT
. GOAL: CUT-TEXT
. . GOAL: HIGHLIGHT-TEXT
[select**: GOAL: HIGHLIGHT-WORD
MOVE-CURSOR-TO-WORD
DOUBLE-CLICK-MOUSE-BUTTON
VERIFY-HIGHLIGHT
GOAL: HIGHLIGHT-ARBITRARY-TEXT
MOVE-CURSOR-TO-BEGINNING 1.10
CLICK-MOUSE-BUTTON
MOVE-CURSOR-TO-END
SHIFT-CLICK-MOUSE-BUTTON 0.48
VERIFY-HIGHLIGHT]
. . GOAL: ISSUE-CUT-COMMAND
MOVE-CURSOR-TO-EDIT-MENU
PRESS-MOUSE-BUTTON
MOVE-CURSOR-TO-CUT-ITEM
VERIFY-HIGHLIGHT
RELEASE-MOUSE-BUTTON

17. . GOAL: PASTE-TEXT
. . GOAL: POSITION-CURSOR-AT-INSERTION-POINT
. . MOVE-CURSOR-TO-INSERTION-POIONT
. . CLICK-MOUSE-BUTTON
. . VERIFY-POSITION
. . GOAL: ISSUE-PASTE-COMMAND
. . . MOVE-CURSOR-TO-EDIT-MENU
. . . PRESS-MOUSE-BUTTON
. . . MOVE-MOUSE-TO-PASTE-ITEM
VERIFY-HIGHLIGHT
RELEASE-MOUSE-BUTTON
TOTAL TIME PREDICTED (SEC)
Based on the above GOMS analysis, it should take seconds to move text.

18. Evaluation Theoretical foundation of HCI
Force to practice of interface design and usability testing
Basic theory of building tools for HCI researcher and practitioners to build models of human behavior
UI design standards and design guidelines
Look and feel

19. Limitations Predictions are only valid for expert users
Experts user can do mistakes
GOMS does not take into account novices
No other metric beside execution time
GOMS has also been criticized for not being representative of current theories of human cognition.
An engineering heuristic, rather than an accurate model of cognitive processes.