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Abstract:
Abstract: The perceived roughness of periodic gratings
increases with increasing groove width (G) or decreasing ridge
width (R), while tactile primary afferent responses depend on G and
grating temporal frequency (F), changes in R being represented only
indirectly through F (Sathian et al., J. Neurosci. 9:1273,1989;
Goodwin et al., ibid, 1280). We asked whether the temporal
information encoded by primary afferents affects roughness
perception. Grating-pairs varying either in G (R constant) or R (G
constant) were scanned over the immobile fingerpad of human
subjects while they discriminated roughness in a two-interval
forced choice. In a control condition, both gratings in a pair were
scanned at constant velocity. Relative to this condition,
discrimination of R (but not G) was significantly impaired when the
grating with the smaller spatial period (P) was scanned at a slower
velocity, keeping F constant. In a third condition, the grating
with the larger P was run at a slower velocity. Relative to
control, this exaggerated the difference in F between gratings in a
pair and tended to improve discrimination of R (where roughness
varies directly with F) but significantly impaired discrimination
of G (where the perceptual effects of F and G oppose each other).
Thus, tactile roughness perception does not depend exclusively on a
spatial coding mechanism (Johnson & Hsaio, Annu. Rev.
Neurosci., 15:227-50, 1992) but also depends importantly on
temporal frequency. Supported by NINDS.
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