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Abstract:
To examine whether or not a learned association between size
and shape can influence the programming of visually guided
grasping, subjects were trained with two sets of plastic objects in
which there was a systematic relationship between size and shape
(circle = large; hexagon = small; or vice versa). Two 'probe'
objects midway in size between the two training sets - one a
circle, the other a hexagon - were used to measure the effect of
the learned size-shape association on size perception and grip
scaling. The probe object matched in shape to the set of small
objects was estimated to be significantly larger than the probe
matched in shape to the set of large objects - a size-contrast
effect. Despite the effect on perception, there was no difference
in preparatory grip scaling when subjects picked up the two probes.
The absence of a size-contrast effect in grip scaling suggests that
visuomotor control is refractory to the learned associations
between size and shape that clearly influence perception, possibly
because varying shape puts high metrical demands on visuomotor
programming.
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