Re: Kosslyn: Mental Imagery

From: Harrison, Richard (
Date: Fri Nov 24 1995 - 17:04:31 GMT

On Kosslyn et al's paper; On the demystification of mental imagery.

As opposed to Pylyshyn who argued that imagery theories are
fundementally flawed and cannot be explanatory, Kossyln says they're
not and suggests what a theory of mental imagery would look like and
presents his own theory and computer model.

The basis of his argument seems to mainly involve empirical evidence.
Two examples, first, the claim that participants take longer to scan
longer distances across images, and second, subjectively smaller images
are more difficult to examine (i.e. as subjectively smaller objects are
more difficult to percieve visually, they are also more difficult to

The second is weaker than the first and can be accomodated in
Pylyshyn's propositional model (e.g. smaller parts involve 'moving
through' more networks) but the first appears to be more challenging.
Kosslyn suggests such observations indicate "that images do represent
metric distance and that this property affects real-time processing
of images." Critcs maintain the effects are due to experimental
demands (participants giving the answers they think experimenters
want to hear). However, even if such an effect doesn't explain the
findings I don't think they need necesserily imply what Kosslyn
concludes. For example, why can't the manipulation of propositions
take different times depending what the proposition are?

A major problem with claiming that mental imagery can be an explanatory
construct is that we cannot know when it is being used by participants
and when it isn't (as well as if they are at all). Also, people do not
report mental representations (as in the computer model) but report
what the objects look like, there seems to be a distinction that is
involved in preventing imagery's explanatory role.

I didn't find this article very convicing as many of the points in
Pylyshyn's critique of imagery were not addressed. For example, the
point that images must be processed before being stored otherwise we
must have an unlimmited storage capacity and our retrieval
characteristics would be different (when something is missing it is
usually an integral thing or a relationship, e.g. remembering who was
at the party but not where they were standing, not arbitary segments
like a torn photograph) were not accounted for in Kosslyn's paper.

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