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?
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 9 can be used for reference on experimental
(i) Short term memory (STM)
The student should first choose an aspect
to investigate: for example, digit span, recency effect,
Example solution: STM decay
- ideally selected to represent population,
more probably undergraduate students (try to get
a range of academic subjects).
Sample size: 10+
- 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.
- Group (b) should be given a task to do during
the delay period in order to avoid rehearsal.
If possible this task should occupy a different
channel to minimise interference, e.g. a visual
- Those in (b) will perform worse than
those in (a) since STM will decay.
- graphs to see decay.
(ii) Long term memory (LTM)
The student should first choose an aspect
to investigate: for example, the total time hypothesis
or the distribution of practice effect.
Example solution: distribution
of practice effect
- as above. Should have no prior experience
of the skill to be learned.
- 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
- Group A will be best (due to the distribution
of practice effect)
(N.B. This one is not easy to run but
could be done with cooperation from friends)
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?
- 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,
- Do the differences suggest different
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.
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
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.
What are mental models, and why
are they important in interface design?
answer available for tutors only
What can a system designer do to minimise
the memory load of the user?
answer available for tutors only
Human short-term memory has a limited
span. This is a series of experiments to determine
what that span is. (You will need some other people
to take part in these experiments with you - they
do not need to be studying the course - try it with
a group of friends.)
(a) Kim's Game
Divide into groups. Each group gathers
together an assortment of objects - pens, pencils,
paper-clips, books, sticky notes, etc. The stranger
the object, the better! You need a large number of
them - at least 12 to 15. Place them in some compact
arrangement on a table, so that all items are visible.
Then, swap with another group for 30 seconds only
and look at their pile. Return to your table, and
on your own try to write down all the items in their
Compare your list with what they actually
have in their pile. Compare the number of things you
remembered with how the rest of your group did. Now
think introspectively: what helped you remember certain
things? Did you recognise things in their pile that
you had in yours? Did that help? Do not pack the things
away just yet.
Calculate the average score for your
group. Compare that with the averages from the other
Questions: What conclusions can
you draw from this experiment? What does this indicate
about the capacity of short-term memory? What does
it indicate that helps improve the capacity of short-term
(b) "I went to market..."
In your group, one person starts off
with "I went to market and I bought a fish"
(or some other produce, or whatever!). The next person
continues "I went to market and I bought a fish
and I bought a bread roll as well". The process
continues, with each person adding some item to the
list each time. Keep going around the group until
you cannot remember the list accurately. Make a note
of the first time someone gets it wrong, and then
record the number of items that you can successfully
remember. Some of you will find it hard to remember
more than a few, others will fare much better. Do
this a few more times with different lists, and then
calculate your average score, and your group's average
Questions: What does this tell
you about short-term memory? What do you do that helps
you remember? What do you estimate is the typical
capacity of human short-term memory? Is this a good
test for short-term memory?
(c) Improving your memory
Try experiment 1.6(a). again, using the
techniques on page 39.
Has your recall ability improved? Has
your group's average improved? What does this show
you about memory?
Locate one source (through the library
or the Web) that reports on empirical evidence on
human limitations. Provide a full reference to the
source. In one paragraph, summarize what the result
of the research states in terms of a physical human
In a separate paragraph, write your thoughts
on how you think this evidence on human capabilities
impacts interactive system design.