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Abstract:
Abstract: Many subjects perceived touch sensations as arising
from a table (or a rubber hand) when both the table (or the rubber
hand) and their own hand were repeatedly tapped and stroked in
perfect synchrony with the real hand hidden from view (Botvinick
& Cohen, 1998; Ramachandran 1998). If a finger on the rubber
hand was then pulled back, a strong skin conductance response (SCR)
was obtained. Similar effects were seen when a band-aid was pulled
off the table. The illusion was not seen if the real hand was
simultaneously visible during stroking and in this condition
(control) SCR was weaker. This suggests that responses were due to
perceptual assimilation of the table (or rubber hand) into one's
body image rather than associative conditioning. Sensations could
even be projected to anatomically impossible distances, and
discrepancies of stroke length between the table and subject's hand
sometimes induced apparent lengthening of the hand. We suggest that
the brain judges it highly improbable that the visual input from
the table and the touch signals from the real hand are identical
sequences merely by chance--instead the brain "decides" the table
or rubber hand must be part of one's own body. These experiments
provide a method for demonstrating the extraordinary malleability
of body image and the Bayesian logic of perception.
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