Re: Motor Imagery

From: Harnad, Stevan (
Date: Mon Oct 30 1995 - 19:45:45 GMT

> From: "Parker, Chris" <>
> Date: Mon, 30 Oct 1995 10:01:46 +0000
> I did not find that motor imagery was well defined!

A visual image is an experience you have that is similar to actually
seeing something, except it's just in your head, you're only imagining
it. A motor image would be the same sort of thing, except instead of
imagining seeing something, you imagine doing something.

> j> One possible explanation for this striking property of visual imagery of
> j> preserving the metric properties of represented objects is that the image
> j> is generated within brain areas which are spatially mapped.
> Can't metric properties also be represented in a distributed way such
> as a coded picture on a floppy disk, where it is the coder/decoder that
> preserves the spatial relationships?

The coder/decoder ENCODES the spatial relationships, but it does not
preserve them SPATIALLY (or in any other continuous dimension that is
one-to-one with space). The topographic areas of the brain preserve
point-to-point nearness relationships in the sensory "shadow" of the
object, and hence in the object itself. Two points that are near one
another in the object will be near one another in the shadow it casts on
the senses, and then this nearness is preserved in the
spatial-map-preserving regions higher in the brain.

The same can be true not only about visual topography ("topography" is
the spatial lay of the land), but about motor topography too. You have
all heard about the sensory "homunculus" -- the inner copies of the
surface of your skin. Well there is a motor homunculus too, which is the
inner copy of the shape and action of your motor end-organs (e.g., your

All this COULD be encoded digitally, described by a series of numbers or
symbols. But it could also be encoded in this analog, spatial-relation
preserving way -- and that's the way the brain appears to do it.

> motor imagery involves a model of "self", and is more complicated [than
> visual imagery]

Is the motor homunculus any more (or less) a "model of self" than the
somatosensory homunculus? And why should an inner copy of the body
surface (and hence of all forms of touch stimulus) be any more or less a
"model of self" than, say a visual copy of a mirror view of the self?

> j> representation
> j> neurons as a common substrate for motor preparation and imagery.
> Is this now saying that a link between perception and motor action is
> the same as between motor preparation and imagery?

Yes, I think J's trying to say that. What do you think of it?

> Motor imagery now has a function and seems to be both the wilful
> calling up of an imagined movement and also a mental representation (a
> correlate of motor preparation).


> A lot of interesting details and ideas, but as brain death approaches
> (this article is the most difficult one to understand that I have ever
> read), I am left wondering if this is THE foundation article or is it
> simply a subtler relation of Lubinski's one on private states?

Lubinsky was the behavioural approach to experience; Jeannerod's is the
neural one. Neither is THE foundation article. We are exploring foundational
questions from different points of view. Let's sample a few more.

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