IE 486 Work Analysis & Design II
Instructor: Vincent Duffy, Ph.D.
Associate Professor of IE
Lecture 8 – Human-Computer Interaction
Thurs. Feb. 8, 2007
IE 486 Lecture 8 - QOTD
Q1. What is a GOMS model? What is the
purpose of a GOMS analysis?
Q2. The case study illustrates which of the
following?
Q3. In a text editing exercise, it is believed that a
user decides to use the mouse to move the
cursor if the cursor is more than 2 lines from
where they will edit the text, but uses the arrow
keys otherwise. In a GOMS model, this
represents…
Usability/HCI Overview
‘Iterative’ cycle for system development.
Criteria for designing usable software
Norman’s ‘Seven stages of action model’ in relation to
goals and actual implemented system
Briefly consider Norman’s ‘Seven stages of action model’
in relation to goals and actual implemented system
GOMS model. What is it; what is the purpose of a
GOMS analysis?
– Review illustration of benefits
Number of users in evaluation – thinking aloud test
Real life example where good/bad computer
interface design can be a life or death matter
Consider the example of Ray Cox at the
East Texas Cancer Center (p.383 in text).
– Technician viewed ‘monitor not plugged in’ as
normal; and she’d used the controls dozens of
times – it was pretty simple.
– However, there was a flaw in the softwarewhen edit function was used very quickly.
Human factors in computers:
– hardware design,
– software functionality,
– interface design.
See ‘iterative’ cycle for system
development.
See Figure 15.1 (p.387 in text).
– Understanding – Design – Evaluation
Understanding
Evaluation
Design
– Other authorities on HCI include: Nielson,
Norman, Landauer
See ‘iterative’ cycle for system
development.
Criteria for designing usable
software (Nielson, 1994)
Learnability
should be easy to learn – to get rapid start in work
Efficiency
So that user has high productivity once learned.
Memorability
Casual user should be able to return after period of time w/out re-learning
Errors
Helpful if system enables low error rate and easy error recovery.
Satisfaction
Pleasant to use; Users should be ‘subjectively’ satisfied.
Priority may be greater or lower based on task characteristics.
– see p.59 in new edition of text (Ch.3 on Usability Testing for additional
information).
Norman’s ‘Seven stages of action model’ in relation
to goals and actual implemented system
See figure 15.2 which consists of two bridges and seven
steps as outlined on p. 390-391 in text.
–
–
–
–
User starts with goals, needs to know what to do, and how
To bridge the Gulf of Execution (bridge)
Bridged (by designer) through good controls (ch.9).
User evaluates to determine (bridge) how well goals matched
results
Execution Bridge
– Intention – send email
– Action specification – necessary sequence
– Interface mechanism
Norman’s ‘Seven stages of action model’ in relation
to goals and actual implemented system
Briefly consider Norman’s ‘Seven stages of action
model’ in relation to goals and actual implemented
system
Evaluation Bridge
– Interface mechanism/display
– Interpretation
– Evaluation
Closing the gap between ‘state of system’
and ‘psychological’ model of system state
is a challenge for designers
QOTD. Q1. What is a GOMS model? What is the
purpose of a GOMS analysis?
See p. 392-393 in text as well as p. 45 in Ch.3 –
considering Task Data).
Goals, Operators, Methods, Selection Rules –
Predictive Models of Task Performance
– Eg. Goal – write email. Sub-goals- make blank page to write on
–
– Methods – sequence of steps – perceptual, cognitive or motor
operators
– Since several methods can be used to achieve the sub-goals,
selection rules are developed/postulated to suggest/identify
under what conditions a user will use one method or another.
– Eg. Method of ‘print’ could be ‘press printer icon’, mouse click
file, print, ok, or choose key sequence (eg. Alt-f-p or Ctrl-p).
– Designers/developers may try to determine when what
conditions lead to certain methods (to predict performance and
learning time).
Recall in HCI: GOMS model & GOMS analysis?
Goals, Operators, Methods, Selection
Rules
– Predictive Models of Task Performance
See p. 392-393 in text as well as p. 45 in Ch.3 –
considering Task Data.
– In HCI this is a keystroke level model of humanmachine interaction
Eg. Goal – write email.
– Sub-goal- make blank page to write on
– So the subgoals can have equivalent related to
the operators
– Eg. Choose menu item ‘compose new email’
Operators are the methods and procedures that
the system makes available
– eg. Elementary motor or cognitive acts needed to
change the system state – for instance, selecting an
item in a menu.
– Or the ‘goal’ to ‘edit chapter 15 title’ might consist of
subgoals with equivalent operators: ‘open file’, find
heading’, ‘delete heading’.
Methods – sequence of steps –
– Perceptual – visual or auditory
– Cognitive – operator decides (next procedures)
whether to listen, respond/speak, or transfer customer
– Motor operations – left hand, right hand, eye
movements
Selection Rules - Since several methods can be used
to achieve the sub-goals, selection rules are
developed/postulated to suggest/identify under what
conditions a user will use one method or another.
– Eg. Method of ‘print’ could be ‘press printer icon’, mouse click
file, print, ok, or choose key sequence (eg. Alt-f-p or Ctrl-p).
– Selection rule: choose mouse if line to be edited is +/- 2 lines
from cursor current position.
Designers/developers may try to determine when what
conditions lead to certain methods (to predict
performance and learning time).
Recall illustration of benefits of using the GOMS
model (NYNEX example).
This case was initially described by Gray et al. 1993
in the journal called Human Computer Interaction.
See p.394 Case study in text.
Gray (1993) et al. used the GOMS model to
‘evaluate’ a new operator workstation for NYNEX
(NY Phone Company).
– Why there was a 3-4% increase in performance time
even though number of keystrokes was reduced?
– (consider the keystrokes on the ‘critical path’)
See also 2 sided handout from ‘Intro to Ergonomics’
Bridger (p.459-461)
– R.S. Bridger, 2003, Introduction to Ergonomics, 2nd Ed., Taylor and
Francis Publishers: UK.
Recall illustration of benefits of using the GOMS
model (NYNEX example).
See also 2 sided handout on course webpage from
‘Intro to Ergonomics’ Bridger (parts of pages 459-461)
Number of users in evaluation
Thinking aloud test –Wickens, see p. 409 in text,
refers to T.Landauer; some refer to J.Nielson (1994).
after 5-6 people, the benefit of additional
people diminishes.
Suggests developers would be better off
making software changes before running
additional subjects.
IE 486 Lecture 8 - QOTD
Q2. The case study illustrates which of the
following?
a. the benefits of a task analysis
b. the barriers to organizational change
c. the information processing model
d. all of the above
e. none of the above
QOTD
Q.3. In a text editing exercise, it is believed that
a user decides to use the mouse to move the
cursor if the cursor is more than 2 lines from
where they will edit the text, but uses the arrow
keys otherwise. In a GOMS model, this
represents…
a. user goals
b. methods
c. cognitive operators
d. all of the above
e. none of the above