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\line{\hss Albert Dvornik}

\centerline{\lf Minds and Machines}
\centerline{\lf Problem Set 11}

\vskip20pt

\problem 1 {\bf ``It resembles my dog''}

The argument makes use of an intuitive, but fallacious understanding
of what mental images are.  If we take the word {\it image} in
``mental image'' literally, it seems natural to believe that a mental
image of a dog resembles the dog.  But is that really so?

Mental images are representations of real world.  What does it mean
for such a representation to resemble something in the real world?  We
can't {\it look} at our mental images: we can have them, they can
perform certain roles in our brain, but we can't get to a mental image
directly.  A mental image of a dog is generated by looking at the dog,
and thus the way the dog looks (and the way each part of the dog
looks, part by part) are aspects of that mental image; but since the
image is built from our observations of the dog, saying that one
resembles the other is a tautology at best, meaningless at worst.

The visual input I get from the photograph of the dog is similar to
the input I get from the dog itself; my experiences and my mental
pictures of the two will, therefore, be similar.  That is the meaning
of saying that the picture resembles the dog.  That, however, says
nothing about my mental imagery of the two.  Similarly, why should the
words ``my dog'' (or, rather, my mental picture of them) resemble my
mental picture of the dog itself, when my experiences of these {\it
two words} must clearly be different from my experiences of a live
animal?

One can see that much of the confusion here comes from the fact that
people tend to put an implicit ``the mental picture of'' in front of
words when discussing mental representations, and then forget about it
and claim that they are talking about a real object.

\vfill\break

\problem 2 {\bf Perky \televenbf Perky \ttenbf Perky \tninebf Perky \teightbf
Perky \tsevenbf Perky \tsixbf Perky \tfivebf Perky}

Perky's experiment clearly does prove that pictures can be confused
with mental images.  That, however, doesn't say much about the nature
of the mental images themselves.

Mental images are similar to perceptions, in the sense that
``replaying'' a mental image is similar to experiencing a perceptual
input.  We expect them to be, since they are generated from
perceptions and since one serves as a reference frame for the other.

Perky's experiment proves this similarity.  It does not prove that the
mental images are picture-like: confusion could also occur if both the
mental representation of Perky's visual stimulus and the mental image
happened to be descriptive.

This idea, however, suggests that one might gain more insight into the
whole debate by investigating where in the thought process the
``mixing'' of the perceptions and images occurs.  If, for instance, we
were to find that the images get ``injected'' directly into the visual
nerve paths somewhere between the eyes and the areas of the brain
responsible for visual processing and analysis, that would constitute
a strong argument that mental images are, in fact, pictorial.  This,
however, seems fairly unlikely.

Without such evidence, I would agree with B's claim that Perky's
experiments just prove mental experiences are similar to perceptual
ones.

\problem 3 {\bf imagery perceptionlike, imagery pictorial}

It doesn't seem too hard to set up an experiment to show imagery is
like perception.  Since imagery is primarily generated by the
perceptual experiences, the experiment needs to show that
quasi-perceptual experiences can be reproduced from mental images.
Since it isn't hard to, for instance, remember ``in your head'' what
someone looks like, he whole idea seems fairly intuitive (although
that intuitive clarity might prove to be a problem).

An experiment to prove that mental imagery is pictorial has a much
tougher task.  It has to show that the mental image is {\it
inherently} pictorial.  That involves showing it behaves in a way that
is ``obviously'' pictorial and not symbolic.  The distinction between
the two is rather blurred; but even if it wasn't, finding evidence
that decidedly supports the pictorialist hypothesis in the eyes of a
skeptical observer would be tricky.

\problem 4

The premises of descriptionalists and pictorialists, the way they are
stated, are mutually exclusive.  Therefore the two groups proceeded to
look for arguments and experiments which would prove their point, and
examining ways of showing that the other side's arguments and
experiments don't {\it really} prove what they claimed they did.  Both
sides seem to have proved that their views are sometimes correct.
Couldn't the truth lie somewhere in between?

Despite their opposition, descriptionalists and pictorialists have
something fascinating in common: both factions believe that the mental
images are represented by a very simple basic scheme (and that, of
course, {\it their} scheme is right).  If we reject both extremes,
we'll have to examine the more complex middle ground between them.

The discussions about the nature of our mental representations involve
{\it mental images} of those mental representations.  But the mental
representations themselves are neither purely ``pictures'' nor
``words''.  It is neither the spatial analogs of the real-world
objects nor their symbolic descriptions that our neurons deal with.
The mental representations might behave like pictures or words under
some circumstances, it seems unlikely that they are purely one or the
other.  In fact, in many respects the two seem almost interchangeable:
every symbol could be graphed by a little icon, every image could be a
word in mentalese.

But looking at it like that, it becomes clear that both concepts are
probably a severe oversimplification of the real state of affairs.
Our brains still seem much more complex than our neurophysiology and
cognitive science, and I seriously think that most real mental images
are neither simple, atomic, discrete symbols nor simple, atomic,
continuous pictures in our heads.  Both descriptive and pictorial
models are nice for analyses of our thought processes, and have some
of basis in reality.  While some people might be more geared toward
one or the other, though, they seem so intermixed that dispute between
the two radical groups seems unreasonable.

It might be-- I'm certainly inclined to believe so-- that the
``pictoral/descriptive'' paradigm might continue to be our best model
for thinking about the images in our mind.  We cannot analyze those
images, whatever their nature might be, by any means other than
``unrolling the mental canvas''; a more agressive analysis will, I
believe, remain stranded in the domain of playing with mental images
of the mental images.  It is precisely that inability to reduce them
to smaller pieces that, in my opinion, makes our mental images such;
if we are to make a thinking machine, either we'll have to figure out
how to deal with this, or we will have to make a machine that uses
fundamentally different imagery-building blocks.
\end
