Mental Images

Reading

Kim Sterelny, "The Imagery Debate"

Ned Block, "Mental Pictures and Cognitive Science"

Lecture where this is primarily covered

• Week 19: 'Representations and Imagery II'
• Week 20: 'Representations and Imagery III'

HOW DO MENTAL IMAGES REPRESENT WHAT THEY ARE IMAGES OF?

It is said that we know that some of the representations in the brain/mind are not structured linguistically: those representations we call mental images.

Pick on a mental image that you can conjure up before your mind's eye.

Note: some people turn out to find this easier than others, and careful accounts based on 'introspection' differ interestingly.

(It has been suggested that some of those most enthusiastic about behaviourism may have had difficulties in forming mental images.)

It seems plausible to say that a mental image is a representation. I.e. is an image of something.

We have discussed how a proposition may represent. (E.g. It may, some people have suggested, picture the thing it is a representation of.)

How does a mental image represent the thing it is an image of?

E.g. I can form easily an image is of the Grand Canal in Venice, from a holiday a long while ago. How does this image of mine represent the Grand Canal?

Does it represent the Grand Canal in the way that a painting of the Grand Canal represents the Grand Canal?

There are said to be two accounts of how mental images represent.

One is that they represent in the way in which pictures represent. This is pictorialism.

The other is that they represent in the way in which propositions represent. This is descriptivism.

Descriptivism is attributed by Sterelny to Pylyshyn:

'...Images are networks of quasi-linguistic representations in a computational workspace.' (Sterelny, in Lycan, p.616.)

If we hold that a mental image represents the thing it is an image of in the same way that a picture represents its subject, we would seem to be committed to the idea that there is a picture, or a quasi-picture, in the mind. It is this picture or quasi-picture that is the mental image. Physicalists will say: if in the mind, then in the brain. So what you are committed to if you believe that mental images represent like pictures do is that there are pictures or quasi-pictures in the brain.

ARGUMENTS FOR THE THESIS THAT 'THERE ARE PICTURES IN THE BRAIN' (MOUNTED BY PICTORIALISM)

1. TELLING WHETHER TWO DIAGRAMS ARE CONGRUENT

The appeal is to an experiment, the gist of which (for our purposes) is:

Two identical diagrams are prepared of the same 3D object.

A is put on the left. B is rotated through say 10 degrees and put on the right.

The pair are shown to the subject, who is asked to say whether the two diagrams are the same. The time it takes for the subject to come up with an answer is noted.

A is put again on the left; B is rotated some more (20 degrees, say).

The new pairing is shown the subject, and the same question is put. The time the subject takes to answer is noted.

This procedure is repeated for larger and larger rotations of B.

What is discovered is that the time it takes the subject to work out whether the two diagrams are the same is linearly related to the degree of rotation of B.

This taken to be evidence that what the brain is doing in answering the question of identity is rotating an image.

This is said to support the pictorial account of what an image is.

2. ACCESSING DIFFERENT POINTS ON A MEMORISED IMAGE.

The subject in this experiment is first asked to memorise a map, which shows a number of features.

The map is withdrawn and the subject is asked to recall it in consciousness, focusing on a particular feature (A).

They are the asked to shift their focus to a different feature (B).

The time it takes to shift the focus is recorded.

They are then asked to return the focus to (A); and then to shift it to a third feature (C)

And so on for all the features.

What is found is that the further A and the new focus are apart on the map, the longer the time it takes to shift focus from A to the new focus.

This is taken as evidence that what the subject is doing in refocusing is working with an image.

There are other arguments.:

INTROSPECTION.

If we are asked to 'look inward' and think about the mental image that we have, most of us will be tempted to say that the mental image is 'like' a picture. (Interestingly, not quite everyone will respond in that way...)

So the argument from introspection, at least as reconstructed by its opponent, Block, is this:

'My mental image of the Grand Canal is pictorial in character, because it is just like the photograph of the Grand Canal that I have in my pocket. I carry the photo around in my pocket, and the mental image around in my head.'

ARGUMENTS AGAINST THE THESIS THAT THERE ARE 'IMAGES IN THE BRAIN' (MOUNTED BY DESCRIPTIVISM)

REJECTION OF THE ARGUMENT FROM INTROSPECTION.

Block says it amounts to this. My experience when I am experiencing a mental image of the Grand Canal is like my experience when I look at a picture of the Grand Canal.

But, says Block, this is not a reason for thinking that my mental image is a picture.

For consider:

The experience I get when I have a mental image is also like the experience I get when I see the Grand Canal for real.

But that doesn't mean that my mental image of the Grand Canal is a canal.

The experience of having a mental   Therefore, a mental image is a       
image of the Grand Canal is like    picture                              
the experience of seeing a picture                                       
of the Grand Canal                                                       

The experience of having a mental   Therefore, a mental image is a       
image of the Grand Canal is like    canal.                               
the experience of seeing the Grand                                       
Canal                                                                    

Does Block's argument fail? At what point?

If I experience x and y as similar it might be because x and y really are similar, but it needn't be.

I may see my psychiatrist as like my father, but that might have nothing to do with any real similarities between the two. It may just be me and my hang-up.

When I experience an image as like a picture, it may be something about me and my relation to these two things that accounts for the experienced similarity.

Here are some other reasons against the thesis that there are 'images in the brain.'

A. THE NO SEUM OBJECTION.

Open up the skull and you don't actually see any images.

B. THE LEIBNIZ LAW OBJECTION.

Phenomenological images are e.g. brilliant blue but bits of the brain do not have the same properties.

(Leibniz Law: 'If a is the very same thing as b, whatever is true of a is true of b.')

C. THE PARAPHERNALIA OBJECTION.

Not only are there no images to be seen when you look at or sections of the brain, there aren't any of the apparatus you would need to work with these images either.

(If images were discovered in the brain, there would also have to be an 'eye' to look at them? If it is true that the brain rotates images, as in the experiment noted, there would have to be an apparatus for carrying out the rotations too.)

FINIS

Review Question

Can you tell, just by thinking about the character of a mental image that you call up and hold before your mind, that it is like a picture?

Poser

If a mental image is not an actual picture, then what is it?