It took ages, so I hope I've read the right thing. I found Jeannerod's
article very interesting and thought most of his arguments very
plausible. As it was so long, there are parts of it which I didn't
fully take in, but I have commented on the parts that struck me
underneath.
> Congenitally blind adults retain a spatial organization of their
> mental imagery (Kerr, 1983). If one assumes that spatial images in
> blind people also correlate with activity of visual cortex, then the
> spatially ordered character of these representations is a logical
> finding.
I have heard that people who are blind from birth are able to
appreciate changes in perceptual size as a function of distance. For
example, a blind person when asked to point to the corners of a wall
will be able to do this fairly accurately from most distances, i.e.
their hands will be wide apart when near the wall and closer
together as they move back. This would also follow from the idea
that the brain has inbuilt spacial understanding.
> At least one clinical case of complete loss of visual imagery with
> preservation of normal visual perception has been reported (Charcot et
> Bernard, 1883)"
That amazes me, I would not have thought it possible to have normal
perception without the corresponding imagery. I thought it had been
demonstrated that perception relies heavily on internal
representations.
> The content of semantic representations can be readily accessed
> consciously; images of visual scenes, faces, words can be generated and
> verbally described. This is not the case for the content of pragmatic
> representations. Although everyone can generate, spontaneously or with
> minimal training, vivid motor images, these images are difficult to
> describe verbally.
I don't necessarily think motor images are difficult to describe.
> Walking times were found to be closely similar to those measured in
> the actual walking condition for the same subjects and for
> corresponding distances.
I'm not so sure that proves anything, maybe the subjects were
consciously trying to match the imagined time taken to the likely
actual time. They may have even believed that was what the
experimenter wanted.
> First, in the clinical domain, it has been observed that Yue and Coe
> (1992) compared the increase in muscular strength produced by actual
> training (repeated maximal isometric contractions) and by mental
> training (imagining the same effortful contractions). In both
> conditions, the maximal force produced by the trained muscles increased
> significantly (by 30% and 22%, respectively). EMG recordings during the
> training sessions showed that, whereas high levels of contraction were
> produced during actual training, the muscle was quiescent during mental
> training.
Wow, that is an incredible result, I wonder if I could tone up my
thighs by imagining a 5 mile jog every morning.
> mental group of patients with prefrontal lesions, who present the
> so-called "utilization behaviour" (Lhermitte, 1983). These patients
> will compulsively imitate gestures or even complex actions performed in
> front of them by an experimenter. Similarly, when faced with usual
> objects (e.g., a glass and a bottle of water) they will not be able to
> refrain from using these objects in a compulsive way (pouring water in
> the glass and drinking large quantities of water, etc).
> This striking behaviour can be explained by an impairment of the
> inhibitory control normaly exerted on the elementary motor schemas.
> In addition, it stresses the role of prefrontal cortex in organizing
> behavioural inhibition. One possible consequence of this impairment
> is that frontal patients presenting this syndrome should be unable
> to generate motor imagery without immediately transferring the
> imagined action into motor output."
These results really do seem to confirm the existence of motor
schemas as proposed by Arbib.
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