1. Human Computer Interaction Lecture 23 Cognitive Models

2. Cognitive Models
Cognitive models claim to have some representation of users as they interact with an interface, that is they model some aspects of the user’s:
understanding, knowledge, intentions or mental processing.
Level of representation differs from technique to technique.

3. Goals vs. Tasks Goals – intentions what you would like to be true.
Goals can be divided into sub-goals.
Tasks – actions
how to achieve the goal or sub-goals.
Task can also be divided into sub-task or smaller tasks(task analysis)

4. Goal and task hierarchies
Mental processing as divide-and-conquer
Example: sales report
produce report
gather data
. find book names
do keywords search of names database
… further sub-goals
filter through names and abstracts by hand
. search sales database - further sub-goals
layout tables and histograms - further sub-goals
write description - further sub-goals

5. Techniques (Models) Cognitive models are classified as below:
Hierarchical models
GOMS(Goals, Operators, Methods, Selection)
Cognitive Complexity Theory (CCT)
Linguistic and grammatical models
BNF (Backus-Naur Form)
Task-Action Grammar (TAG)
Physical and device-level models
Keystroke-Level Model
Three State Model

6. GOMS Goals what the user wants to achieve Operators
basic actions user performs
Methods
decomposition of a goal into subgoals/operators
Selection
means of choosing between competing methods

7. GOMS Example-1 GOAL: CLOSE-WINDOW . [select Sub GOAL: USE-MENU-METHOD
. MOVE-MOUSE-TO-FILE-MENU
. PULL-DOWN-FILE-MENU
. CLICK-OVER-CLOSE-OPTION
Sub GOAL: USE-CTRL-W-METHOD
. PRESS-CONTROL-W-KEYS]
For a particular user:
Rule 1: Select USE-MENU-METHOD unless another
rule applies
Rule 2: If the application is GAME,
select CTRL-W-METHOD

8. GOMS Example-2 Goal: delete a word in a sentence
Method-1 for accomplishing goal of deleting a word using menu option:
Step1. Recall that word to be deleted has to be highlighted
Step2. Recall that command is “cut”
Step3. Recall that the command “cut” is in edit menu
Step4. Accomplishing goal of selecting and executing the “cut” command
Step5. Return with goal accomplished

9. GOMS Example-2
Method-2 for accomplishing goal of deleting a word using delete key:
Step1. Recall where to position cursor in relation to word to be deleted
Step2. Recall which key to delete each letter
Step3. Press “delete” key to delete each letter
Step4. Return with goal accomplished

10. GOMS Example-2 Operators to use in above methods: Click mouse
Drag cursor over text
Select menu
Move cursor to command
Press keyboard key

11. GOMS Example-2 Selection Rules to decide which method to use:
1: Delete text mouse and selecting from menu if large amount of text is to be deleted
2: Delete text using delete key if small number of letters are to be deleted

12. Cognitive Complexity Theory
Cognitive complexity is the psychological characteristic or variable that shows how complex or simple the frame and perceptual skill of a person are. It is the extent to which a person differentiates and integrates an event.
Two parallel descriptions:
User production rules
Device generalised transition networks
Production rules are of the form:
if condition then action