The Illusion of Mental Pictures. Zenon Pylyshyn Rutgers University, Center for Cognitive Science http:/ruccs.rutgers.edu/faculty/pylyshyn.html. The illusion of mental pictures.
The Illusion of Mental Pictures
Center for Cognitive Science
The intentional or phenomenological fallacy.
We are all inexorably drawn to confusing properties of the imagined world with properties of our image of it.
Consider the power of this draw to the object, whichWundt called the Stimulus Error.
Examples to probe your intuition and your tacit knowledge
Suppose you get this pattern:
What is responsible for this pattern in your image?
Time since first drop
Two complementary colored light beams => white
Two complementary colored filters or paint => black
Is there conservation of volume in your image? If not, why not?
That’s all I have to say about the status of conscious experience as a basis for building a scientific theory of mental processes – I hope it’s enough to raise some skepticism. I have more to say about this issue in my 2007 book;
Things and Places; How the mind connects with the world MIT Press (paperback 2010)
The most interesting questions about mental imagery come together in the problem of representing spatial patterns
Representation of Space in Mental Images
This is the issue I am most interested in because it bears on some questions about how visual information is encoded as well as the vexing question of the role of conscious experience in cognitive science
“A depictive representation is a type of picture, which specifies the locations and values of configurations of points in a space. … In a depictive representation, not only is the shape of the represented parts immediately available to appropriate processes, but so is the shape of the empty space … Moreover, one cannot represent a shape in a depictive representation without also specifying a size and orientation….”
Time to judge whether (a)-(b) or (b)-(c) are the same except for orientation increases linearly with the angle between them (Shepard & Metzler, 1971)
Is this how the process looked to you?
When you make it rotate in your mind, does it seem to retain its rigid 3D shape without re-computing it?
“If visual-image rotation uses a spatial medium [referred to as functional space], then images must traverse intermediate positions when they rotate from one position to another. A [symbolic] system can be designed to represent intermediate positions during rotation, but that is not obligatory.”
Clarifying the Obligatory requirement
Direction of tape motion
The Moral: Regularities in behavior may be due to either:
The inherent nature of the system or its structure or its architecture.
The content of what the system represents(what it “knows”).
A window on the mind
(Pylyshyn & Bannon. Described in Pylyshyn, 1981)
(Pylyshyn & Bannon. Described in Pylyshyn, 1981)
The central problem with imagistic explanations…
Time =distance speed
But what ensures that a corresponding relation holds in an image? The obvious answer is: Because the image is laid out in real space!
To use Prinz’s term, it is not obligatory that the well-known relation between distance, speed and time hold in functional space or in a matrix. There is no natural law or principle that requires it. You couldimagine an object moving instantly or according to any motion relation you like, and the functional space would then be made to comply with that since it has no constraints of its own.
The good news for picture theories
There is a topographical projection of retinal activity on the visual cortex of the cat and monkey.
Tootell, R. B., Silverman, M. S., Switkes, E., & de Valois, R. L. (1982). Deoxyglucose analysis of retinotopic organization in primate striate cortex. Science, 218, 902-904.
The bad news for picture theories
But the explanation for why large visual objects activate more frontal parts of the visual cortex depends on the fact that fibers from parafoveal cells connect to these frontal areas. This can’t be the case with mental images unless they are also on the retina!
And anyway, how does the fact that large mental images activate frontal parts of the visual cortex explain why small details are easier to detect in large mental images? Or how does it explain why scanning across a large image takes longer just because it happens to lie in the more fontal visual cortex? All picture-theory explanations make essential reference to distances and sizes.
Many neuroscience explanations for imagery findings make exactly the same mistake of citing activation patterns that arise from connections to the retina, and which therefore do not work unless mental images are projected onto the retina. I will give just one more example of a such a neural explanation because the error in that case is particularly egregious.
The proportion of Vertical, Horizontal & Oblique cells remains the same in all cases – they are located at random on the surface of visual cortex!
The image scanning effect was shown to be Cognitively Penetrable.But what allows a smooth scan across the image is the perceptual display. Without the perceived map scanning would not be smooth and continuous and the timing would not be accurate (Pylyshyn & Cohen, 1999).