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Abstract:
If naïve subjects are asked to compare the perceived
weight of a large object with that of a small object of identical
physical weight, the small object feels substantially heavier - the
size-weight illusion (SWI). Perhaps you expect the large object to
be heavier and set your muscles accordingly, andit therefore feels
lighter than the small object. We have previously shown (Hubbard et
al., Soc. Neurosci. Abs., 30, 457) that subjects adapt to perceived
weight differences caused by the SWI rather than physical wieght.
After holding two objects of equal weight, but differing in size,
subjects consistently report that the hand that held the smaller
object during the adaptation phase holds the lighter weight when
tested with two equal weights. We report two new experiments: 1)
When the weight of the larger object is increased so that the two
objects feel the same, there is no aftereffect, even though the
larger object weighs more twice the smaller one 2) When two same
size objects with an objective weight difference equivalent to that
caused by the SWI are held, the aftereffect is no larger than that
caused by the illusion. These results demonstrate the neural locus
of the size-weight illusion precedes that of adaptation, and
therefore adaptation occurs at a higher level in the nervous
system.
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