Re: More on geometric description.
Dennis Lomas
haven't had time to participate until now.
Steven Lehar's work was referred to earlier in this discussion. Here is the
concluding couple of sentences from his BBS paper.
"The central message of Gestalt theory therefore is that the primary function
of perceptual processing is the generation of a miniature, virtual-reality
replica of the external world inside our head, and that the world we see around
us is not the real external world, but is exactly that miniature internal
replica (Lehar 2003). It is only in this context that the elaborate model
presented here begins to seem plausible." (BBS 2004)
I have a few questions: How does this this model incorporate bodily
representations, e.g., of a foot or arm? Specifically, is perception of a foot or arm
(as in my perceiving my arm before me now as I type) part of the replica of the
external world? If so, then how does this accord with the above assessment?
That is, is my perception of my foot or arm part of a "virtual-reality replica
of the external world" and so on.
Dennis Lomas
University of Prince Edward Island
Steven Lehar
Lomas >
I have a few questions: How does this this model incorporate bodily
representations, e.g., of a foot or arm? Specifically, is perception of a
foot or arm ... part of the replica of the external world? If so, ... is my
perception of my foot or arm part of a "virtual-reality replica
of the external world"?
< Lomas
Yes it is. This is clear from the phantom limb syndrome, where amputees
feel the vivid spatial presence of a limb that no longer exists. They could
show us the exact limits of the arm that they experience, revealing a
spatial structure that does not even necessarily conform to the geometry of
the missing limb. The limbs tend to morph gradually over time to a shorter
arm or leg, with a larger hand or foot, as if the perceived limb were
gradually morphing to match the sensorimotor "homunculus" on the cortical
surface with its exaggerated hands and feet.
A real arm is perceived visually to be in register with the somatosensory
or proprioceptive arm, they "lock on" to each other like left and right
images in binocular vision, that merge together to create a single
experience in which you can no longer tell which eye is contributing to
which parts of the experience. Ramachandran has even cured people with
painful phantom limb syndrome using this phenomenon. For example an amputee
might feel a painful tension in his phantom fist because he cannot relax
the fingers from their tight knotted grip. So Rama sets up a mirror edge-on
in front of them, to put a visual reflection of his left arm to superimpose
on the missing void of his right arm. The patient believes that they are
seeing the missing limb visually. When asked to extend and contract the
fingers of both hands simultaneously, they feel for the first time that
they have control over their missing phantom limb, and the release of
tension relieves the pain.
The relation between the visual world and the somatosensory /
proprioceptive world is explained here:
http://cns-alumni.bu.edu/~slehar/cartoonepist/cartoonepist44.html
Steve