Web Resources | Assignment
Comments | Teaching
When doing this exercise
you will probably be surprised at just how little you know
about how ATMs work (unless you have worked in a bank). A
main reason being that, as far as you are concerned, an ATM
is there to serve you efficiently and effectively. You just
need to know how to operate it. It is only when unexpected
things happen (e.g. it does not give you any money, it says
you are overdrawn when you are not, it gives you more money
than you asked for) that you may start to wonder how an ATM
Some of the questions we ask in the assignment
are difficult to answer. For example, what information is
on your card? All you can see is a magnetic strip on the back
of the card. You have never been told what is written on it.
You have to infer from your knowledge of banking what might
be on it. This is likely to include your password, your account
number and your limit. But what else?
Most of us are unlikely to have thought much
about many of the questions asked in the assignment. So we
make inferences on the spot from our limited knowledge about
such systems. This is what we mean by ad hoc reasoning. We
also will commonly use analogies, e.g. 'well it is like a
debit card', in an attempt to explain. Some of these maybe
appropriate and others not.
What did you find when you asked other people?
You may have discovered that their explanations were quite
different. It is quite common for there to be variability
between people's explanations of the same system. Also did
you find that people used incorrect analogies, superstition
and bizarre models to explain their understanding? People
can be quite creative when forced to provide explanations
when they have no idea!
Another issue that is important to think about
is whether you really are eliciting a person's mental model,
when asking such questions. How do you know what they say
reflects the knowledge they use when interacting with a device?
This question has taxed researchers for many years and there
is a whole literature on how to elicit mental models and how
to determine whether they are really the knowledge representations
people use in their activities.
When ATMs first came out, different conceptual
models were used by the different banks in the design of their
ATMs. A key aspect was whether to (i) let the person take
their money first and then give their card back or (ii) give
their card back before letting them take their money. Banks
that designed their ATMs on the first model found that a surprisingly
high number of people forgot to take their card once they
had achieved their primary goal of obtaining their cash. Conversely,
banks that designed their machines using the second model
didn't experience such problems. People rarely left their
cash behind once they had removed their card! From an engineering
perspective, the order in which they are performed may be
regarded as arbitrary (so long as they are both executed).
From an interaction design perspective, it is obvious as to
why the order in which they are carried out by the user is