Page 124 -

3.4 Conceptual frameworks for cognition 93

an average citizen is likely to have a reasonably good mental model of how to oper-
ate a TV but a "shallow" mental model of how it works.
Within cognitive psychology, mental models have been postulated as internal
constructions of some aspect of the external world that are manipulated enabling
predictions and inferences to be made (Craik, 1943). This process is thought to in-
volve the "fleshing out" and the "running" of a mental model (Johnson-Laird,
1983). This can involve both unconscious and conscious mental processes, where
images and analogies are activated.

o illustrate how we use mental models in our everyday reasoning, imagine the following

(a) You arrive home from a holiday on a cold winter's night to a cold house. You have a
small baby and you need to get the house warm as quickly as possible. Your house is
centrally heated. Do you set the thermostat as high as possible or turn it to the de-
sired temperature (e.g. 70°F)?
(b) You arrive home from being out all night, starving hungry. You look in the fridge and
find all that is left is an uncooked pizza. The instructions on the packet say heat the
oven to 375°F and then place the pizza in the oven for 20 minutes. Your oven is elec-
tric. How do you heat it up? Do you turn it to the specified temperature or higher?

Comment Most people when asked the first question imagine the scenario in terms of what they would
do in their own house and choose the first option. When asked why, a typical explanation
that is given is that setting the temperature to be as high as possible increases the rate at
which the room warms up. While many people may believe this, it is incorrect. Thermostats
work by switching on the-heat and keeping it going at a constant speed until the desired tem-
perature set is reached, at which point they cut out. They cannot control the rate at which
heat is given out from a heating system. Left at a given setting, thermostats will turn the heat
on and off as necessary to maintain the desired temperature.
When asked the second question, most people say they would turn the oven to the speci-
fied temperature and put the pizza in when they think it is at the desired temperature. Some
people answer that they would turn the oven to a higher temperature in order to warm it up
more quickly. Electric ovens work on the same principle as central heating and so turning
the heat up higher will not warm it up any quicker. There is also the problem of the pizza
burning if the oven is too hot!

Why do people use erroneous mental models? It seems that in the above sce-
narios, they are running a mental model based on a general valve theory of the way
something works (Kempton, 1986). This assumes the underlying principle of "more
is more": the more you turn or push something, the more it causes the desired ef-
fect. This principle holds for a range of physical devices, such as taps and radio con-
trols, where the more you turn them, the more water or volume is given. However,
it does not hold for thermostats, which instead function based on the principle of
an on-off switch. What seems to happen is that in everyday life people develop a
core set of abstractions about how things work, and apply these to a range of de-
vices, irrespective of whether they are appropriate.