Re: The Homunculus

From: HARNAD Stevan (
Date: Wed May 08 1996 - 16:05:37 BST

> From: Whitehouse Chantal <>
> Date: Wed, 8 May 1996 13:24:34 GMT
> I understand the normal homunculus problem but I'm unsure
> about what the "somatosensory homunculus" is. Could you
> please tell me the difference?

The somatosensory homunculus is exactly analogous to the retinotopic map
(remember, the analog shadow cast on the retina, analogs of which are
copied at higher and higher levels in the brain while preserving local
topoography and connectivity?) discussed in the lectures and by Kosslyn
as well as Posner. If you understand the retinototopic map in the case
of vision, then just translate vision into touch, and you have the
somotosensory homunculus: a point-for-point map of your skin surface,
copied to a higher level of your brain, preserving the local topography
and connectivity.

By the way, besides the somotosensory (skin) homunculus, there is also
the motor homunculus, which is an inner analog projection of all of your
moving surfaces. Both are "shaped" roughly like a little man, though
some parts are exaggerated (e.g., the fingers get much more extensive
and sensitive representation than the elbows); in the same way, the
fovea, or centre of vision, has more area devoted to it in the
retinotopic map than the peripheral parts of the retina, the outer parts
of your visual field.

Now Chantal knows the difference between this kind of homunculus, which
is really just an internal analog projection or "shadow" of the sensory
and motor surfaces of the body, and the other kind of homunculus, the
kind that creates a problem. Does everyone else know? Would anyone care
to explain the difference?

Hint: The sensorimotor homunculi are literally point-for-point internal
re-projections or analog copies of the sensorimotor surfaces. The
mentalistic homunculus is an analog "I," a mind within a mind, that is a
"copy" of ME: But surely one me is enough! So to explain me, you had better
not make use of yet another (unexplained) me...

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