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Abstract:
To examine whether or not a learned perceptual association
could influence the programming of visually guided grasping,
subjects were trained with a set of objects in which there was a
systematic relationship between size and shape. In Exp. 1, the
association was established by affixing a single 2-D drawing of a
shape to the top surface of large and small square wooden blocks
(e.g. triangle = large; circle = small, or vice versa). In Exp. 2,
the same association was established, but this time multiple 2-D
shapes covered the surface of the blocks (creating a pattern of
either triangles or circles). Two test blocks midway in size
between the large and small blocks - one matched by the shape cue
to the large blocks, the other to the small blocks - were used to
measure the effect of the learned size-shape association on size
perception and grip scaling. In both experiments, the test block
matched by the shape cue to the small blocks was estimated to be
significantly larger than the test block matched by the shape cue
to the large blocks - a size-contrast effect. Despite the
significant effects on perception, a corresponding effect on
preparatory grip scaling was seen only in Exp. 2. Apparently,
visuomotor programming makes use of perceptual information only
when the cue underlying the learned association covers the target's
surface, creating a prominent surface texture.
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