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Abstract:
The perceived roughness of periodic gratings of alternating
ridges and grooves is influenced by both groove width (GW) and
ridge width (RW). When a grating is scanned across the skin, its
cycles (each composed of a ridge and groove) pass in succession
with a temporal frequency (F) determined by the scanning speed and
the width of the cycle. The effect of RW on roughness depends on F,
while that of GW is relatively independent of temporal factors
(Cascio & Sathian, Soc. Neurosci. Abstr. 26:156.6, 2000). As a
baseline for comparison with abnormal populations, we tested the
ability of healthy volunteers to discriminate the roughness of
gratings scanned at varying speeds over the immobile fingerpad,
using a two-interval forced-choice paradigm. As expected, roughness
discrimination for GW-varying gratings was unaffected by speed
changes. Unexpectedly, discrimination of roughness based on RW
variation was impaired, but only at slow speed. We speculate that
absolute differences in F between RW-varying gratings scanned at a
slow speed may be too small to permit roughness discrimination.
However, when speed (and thus F) increases, the same relative
differences in F are larger in absolute magnitude and could hence
be reliably discriminated. These findings reinforce the idea that
temporal factors are important in judging the roughness of gratings
varying in RW, but not GW.
Supported by NINDS
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