Chapter 1

The Human

1.1 Devise experiments to test the properties of (i) short-term memory (ii) long term memory, using the experiments described in this chapter to help you. Try out your experiments on your friends. Are your results consistent with the properties described in this chapter?

answer

The aim of this exercise is to get the student to think about experimental design. The experiments devised can effectively be repeats of the originals. Chapter 11 can be used for reference on experimental design.

(i) Short term memory (STM)

The student should first choose an aspect to investigate: for example, digit span, recency effect, decay.

Example solution: STM decay

Subjects

ideally selected to represent population, more probably undergraduate students (try to get a range of academic subjects).
Sample size: 10+

Experiment

split subjects into two groups. Each subject studies list of 15-20 words (could try with both nonsense words and actual words to see any difference). Subject has to recall list either (a) immediately or (b) after 20 second delay. Measure the number (or percentage) of the words remembered correctly.

A within-groups design can be used to avoid individual bias or group variation (as long as different lists are used for each attempt).

independent variable -- delay in recall
dependent variable -- number correctly recalled.

Hypothesis

Those in (b) will perform worse than those in (a) since STM will decay.

Analysis

graphs to see decay.
T test

(ii) Long term memory (LTM)

Example solution: distribution of practice effect

Subjects

as above. Should have no prior experience of the skill to be learned.

Experiment

split subjects into 3 groups. Each subject must learn a skill (for example shorthand or typing -- must be measurable). Group A learns for 1 hour a week for 6 weeks. Group B learns for 2 hours a week for 3 weeks. Group C learns for 3 hours a week for 2 weeks.

After each group's training is complete the subjects are tested and the number of mistakes made are noted.

Between-groups design.

independent variable -- style of learning
dependent variable -- accuracy

Hypothesis

Group A will be best (due to the distribution of practice effect)

Analysis

ANOVA

(N.B. This one is not easy to run but could be done with cooperation from friends)

1.2 Observe skilled and novice operators in a familiar domain: for example, touch and 'hunt-and-peck' typists, expert and novice game players, or expert and novice users of a computer application. What differences can you discern between their behaviours?

answer

• This is an exercise in observation.
  The student should think about skill acquisition, proceduralization, chunking, etc.
• Is there any evidence of this in practice?
• How do the groups differ (speed, error, style, strategy)?
• Do the differences suggest different skill levels?

1.3 From what you have learned about cognitive psychology, devise appropriate guidelines for use by interface designers. You may find it helpful to group these under key headings: for example, visual perception, memory, problem solving, etc, although some may overlap such groupings.

answer

Guidelines are just what they say they are: guidelines. They provide for a consistent look and feel for an interface, as well as trying to exclude the more obvious mistakes that can be made from a psychological perspective. However, there are occasions when such constraints should be broken; for new interaction devices, for example, or to create a unique style of product.

Because of this, there is no one correct answer to this question: some will be more cognitively friendly than others, that is all. Guidelines can range from the general principle type shown below down to highly detailed information on what each component in a display should look and behave like.

Some examples of guidelines with cognitively solid foundations are shown below - this is not an exhaustive set by any means.

• Colour: don't show details in blue. Remember certain users can confuse green and red. Remember the social expectations of colours (e.g., in Western culture, red - stop, danger, hot; blue - cold; green - go).

• Text: don't use all capital letters in text. Use a serif font for large blocks of text. Dark characters on a light screen are read more accurately and preferred.

• Functionality: limit the number of things to be remembered to 7, and preferably to 5. Group things according to function.

• Problem solving: use analogy and metaphor to aid learning and performance.

This exercise should encourage students to look into the literature on human factors, cognitive psychology and human physiology, and come up with some hard evidence about human limitations. This can then be used to provide informed guidelines. The results of a similar exercise can be seen in some Example Guidelines produced by students.

Worked exercises

• Suggest ideas for an interface which uses the properties of sound effectively. [page 24]

• Identify the goals and operators involved in the problem 'delete the second paragraph of the document' on a word processor. Now use a word processor to delete a paragraph and note your actions, goals and subgoals. How well did they match your earlier description? [page 42]

• Produce a semantic network of the main information in this chapter. [page 50]

HCI 2e home page || changes and additions || resources || search || contents || authors || ordering
feedback to feedback@hcibook.com http://www.hcibook.com/hcibook/	designed and hosted by hiraeth mixed media webmaster@hiraeth.com