12. cognitive models


Recall the CCT description of the rule INSERT-SPACE-2 discussed in Section 12.2.2:

	IF (AND (TEST-GOAL insert space)
		(DELETE-GOAL insert space) ))

As we discussed, this is already proceduralized, that is the rule is an expert rule. Write new 'novice' rules where the three keystrokes are not proceduralized. That is, you should have separate rules for each keystroke and suitable goals (such as GET-INTO-INSERT-MODE) to fire them.


IF (AND (TEST-GOAL insert space)
(TEST-NOTE in command mode ))
THEN ( (ADD-GOAL get into insert mode)))
IF (AND (TEST-GOAL insert space)
(TEST-GOAL get into insert mode))
(ADD-NOTE in insert mode)
(DELETE-GOAL get into insert mode)))
IF (AND (TEST-GOAL insert space)
(TEST-NOTE in insert mode)
(ADD-GOAL get into command mode)))
IF (AND (TEST-GOAL insert space)
(TEST-NOTE in insert mode)
(TEST-GOAL get into command mode))
(DELETE-GOAL get into command mode)
(DELETE-GOAL insert space)
(DELETE-NOTE in insert mode)
(ADD-NOTE in command mode)))



One of the assumptions underlying the programmable user model approach is that it is possible to provide an algorithm to describe the user's behaviour in interacting with a system. Taking this position to the extreme, choose some common task with a familiar interactive system (for example, creating a column of numbers in a spreadsheet and calculating their sum, or any other task you can think of) and describe the algorithm needed by the user to accomplish this task. Write the description in pseudocode. Does this exercise suggest any improvements in the system?


open-ended exercise

Individual exercises

ex.12.1 (ans), ex.12.2 (ans)

Worked exercises in book


Create a GOMS description of the task of photocopying a paper from a journal. Discuss the issue of closure (see Chapter 1) in terms of your GOMS description. [page 424]


Do a keystroke-level analysis for opening up an application in a visual desktop interface using a mouse as the pointing device, comparing at least two different methods for performing the task. Repeat the exercise using a trackball. Discuss how the analysis would differ for various positions of the trackball relative to the keyboard and for other pointing devices. [page 440]

  • a worked exercise
  • a worked exercise