Re: Motor Imagery

From: Lucas, Melody (
Date: Mon Oct 30 1995 - 18:43:57 GMT

That was a rather groovy (if lengthy) article. He really did do a good
job of trying to reach the 'neurophysiologist's dream'. Representations
are surely the things we need to study since all experience is
representations in some form or other. Hats off to Jeannerod because he
attempted to identify, classify and implement these representations in
physiological terms. The article was a bit too extensive to cover
everything, so I've just commented on the areas which struck me as
being especially interesting, dodgy or confusing!

> At least one clinical case of complete loss of visual imagery with
> preservation of normal visual perception has been reported (Charcot et
> Bernard, 1883). Much more recently, the reverse situation has been
> observed by Behrmann et al (1992). They reported the case of one
> agnosic patient who was unable to recognize visual objects (face
> recognition, however, was preserved), but had intact visual imagery
> ability.

I wonder how the loss of visual imagery affects memory of visual
events. Is imagery involved in rehearsal or is this a completely
different part of the brain? What makes face recognition so special?

> An example can be used to illustrate this point. Consider for example
> the teacher and pupil situation during the action of learning a motor
> skill like playing a music instrument. The pupil watches the teacher
> demonstrating an action, with the instruction of later imitating and
> reproducing that action. Although the pupil remains immobile during the
> teacher's demonstration, he must image in his mind the teacher's
> action. Conversely, when the teacher watches the pupil's repetition, in
> spite of not performing the action himself, he will experience a strong
> feeling of what should be done and how this could be done. Similar
> feelings may be experienced by sport addicts watching a football game
> on television. They must play in their mind the appropriate action to
> catch the ball (and indeed, they express their frustration when the
> ball has been missed by the player). The vividness of the imagined
> action can be such as to induce in the watchers changes in heart and
> respiration rates related to the degree of their mental effort (see
> Section 3.3).

Excellent! Cardio-vascular exercise whilst watching TV (and they call
our generation couch potatoes!) On a serious note, this really does
support the 'common substrate' idea.

> Adams et al. (1987) have shown that heart rate and cardiac output
> already show a noticeable increase within about 5 beats after exercise
> is started. Respiration changes within one breathing cycle. These
> effects can hardly be explained by metabolic factors, since a reflex
> increase in heart rate based on CO2 increase in veinous blood should
> take a longer time. A plausible explanation is that vegetative
> activation during preparation to effort would be timed to begin
> slightly prior to the time when motor activity starts. This would
> represent an optimal mechanism for anticipating the forthcoming
> metabolic changes (by increasing perfusion of muscles with oxygenated
> blood) and shortening the intrinsic delays needed for heart and
> respiration to adapt to effort.

This implies an evolutionary back-up to Jeannerod's ideas.

> The object attributes are represented therein as affordances, that is,
> to the extent that they afford specific motor patterns, not as cues for
> a given perceptual category

This supports previous studies concerning pragmatism and one can
logically allow evolutionary 'law' to explain the occurence of such a

> The higher level is more difficult to describe in neurophysiological
> terms. The functional operations underlying motor planning, preparation
> and imagery must involve large neuronal ensembles, which are likely to
> be widely distributed. In addition, high-order representation neurons
> should encode complex goals, not only affordances.

I'm not too sure about this one. This idea of a hierarchical model... I
don't like models because they're not absolute! The problem is probably
more likely to be that I'm tired and it has taken me hours to finish
this. I'd like to understand it, though- perhaps tomorrow!

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