Introspective intuition can easily lead to the idea that many of our
cognitive tasks are achieved via mental imagery. However, Pylyshyn
asked the question, who was looking at these images and what were
they doing with them. He made the point that this does not give any
explanatory role to images at all, it just pushes the explanation
deeper into the system. He claims therefore that to explain anything
by use of mental imagery is to be homuncular and lead to infinite
regress.
His alternative is that our minds can be seen as a software
programme, and we manage to do the things we do, not by mental
imagery, but by following a set of propositional rules. These he
believes are built into the system, and are sufficient to account for
our information processing abilities. However, if propositional rules
are built into the system, there must be someone inside to interpret
them as, for example saying if a then b, doesn't make any sense.
Also, is it any less credible that mental images could be hardwired
into our brains in the same way. These points challenge Pylyshyn's
claim that his computational approach is significantly less
homuncular.
There are many occasions when mental imagery is a more useful tool in
problem solving than propositional debates. Roger and Shephard, for
example, show that translating 2D images into 3D images is more
difficult to do using propositions, than it is by visualisation.
Similarly, Jeannerod gives many examples of how the neural substrates
of motor imagery can be elucidated, and how these are coupled
directly to motor preparation and motor action.
Kosslyn, in particular takes on Pylyshyns challenge, and undertakes a
series of experiments which aim to show that mental imagery is
involved in cognitive tasks. He shows, for example, that people take
the same time to mentally scan an imagined map, as they would do a
real map. Unfortunately, it is very difficult to be sure that Kosslyn
is really measuring scanning times, as opposed to other factors such
as subject expectations etc. Pylyshyn counters many of Kosslyns
conclusions, by saying that the subjects could be reaching their
conclusions computationally, and that differences in scanning times
could just as easily be accounted for by the length of time required
to compute the answer, as it could by the time taken to scan the internal
image.
This archive was generated by hypermail 2b30 : Tue Feb 13 2001 - 16:23:57 GMT