The Journal of Neuroscience, September 1, 2001, 21(17):6905-6916
Neural Coding Mechanisms Underlying Perceived Roughness of Finely
Textured Surfaces
Takashi
Yoshioka,
Barbara
Gibb,
Andrew K.
Dorsch,
Steven
S.
Hsiao, and
Kenneth O.
Johnson
Zanvyl Krieger Mind/Brain Institute, Departments of Neuroscience
and Biomedical Engineering, Johns Hopkins University, Baltimore,
Maryland 21218
Combined psychophysical and neurophysiological studies have shown
that the perceived roughness of surfaces with element spacings of >1
mm is based on spatial variation in the firing rates of slowly adapting
type 1 (SA1) afferents (mean absolute difference in firing rates
between SA1 afferents with receptive fields separated by ~2 mm). The
question addressed here is whether this mechanism accounts for the
perceived roughness of surfaces with element spacings of <1 mm. Twenty
triangular and trapezoidal gratings plus a smooth surface were used as
stimulus patterns [spatial periods, 0.1-2.0 mm; groove widths (GWs),
0.1-2.0 mm; and ridge widths (RWs), 0-1.0 mm]. In the human
psychophysical studies, we found that the following equation described
the mean roughness magnitude estimates of the subjects accurately (0.99 correlation): 0.2 + 1.6GW 
0.5RW 0.25GW2. In the neurophysiological studies, these
surfaces were scanned across the receptive fields of SA1, rapidly
adapting, and Pacinian (PC) afferents, innervating the glabrous skin of
anesthetized macaque monkeys. SA1 spatial variation was highly
correlated (0.97) with human roughness judgments. There was no
consistent relationship between PC responses and roughness judgments;
PC afferents responded strongly and almost equally to all of the
patterns. Spatial variation in SA1 firing rates is the only neural code
that accounts for the perceived roughness of surfaces with finely and
coarsely spaced elements. When surface elements are widely spaced, the
spatial variation in firing rates is determined primarily by the
surface pattern; when the elements are finely spaced, the variation in firing rates between SA1 afferents is determined by stochastic variation in spike rates.
Key words:
roughness; tactile; somatosensory; grating; fine texture; peripheral nerve; SA1; RA; PC; psychophysical roughness magnitude; macaque; mechanoreceptor
Copyright © 2001 Society for Neuroscience 0270-6474/01/21176905-12$05.00/0
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