Tactile Discrimination of Gaps by Slowly Adapting Afferents: Effects of Population Parameters and Anisotropy in the Fingerpad
Department of Anatomy and Cell Biology, University of Melbourne, Parkville, Victoria 3052, Australia Wheat, Heather E. and Antony W. Goodwin. Tactile Discrimination of Gaps by Slowly Adapting Afferents: Effects of Population Parameters and Anisotropy in the Fingerpad. J. Neurophysiol. 84: 1430-1444,...
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Published in | Journal of neurophysiology Vol. 84; no. 3; pp. 1430 - 1444 |
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Main Authors | , |
Format | Journal Article |
Language | English |
Published |
United States
Am Phys Soc
01.09.2000
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Subjects | |
Online Access | Get full text |
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Summary: | Department of Anatomy and Cell Biology, University of Melbourne,
Parkville, Victoria 3052, Australia
Wheat, Heather E. and
Antony W. Goodwin.
Tactile Discrimination of Gaps by Slowly Adapting Afferents:
Effects of Population Parameters and Anisotropy in the Fingerpad. J. Neurophysiol. 84: 1430-1444, 2000. The aim
of this study was to determine the acuity of the peripheral tactile
system for gaps and to determine how stimulus orientation may impact on
this. We quantified the ability of humans to discriminate small
differences in gap width using a forced-choice task. Stimuli were
presented passively to the distal fingerpad in a region where the skin
ridges all run approximately in the same direction. Two standard gap
widths were used (2 and 2.9 mm), and the comparison gap widths were
larger than the standard gaps. With the gap axis parallel to the skin
ridges, the average difference limen was approximately 0.2 mm for both
standards. We examined the effect of stimulus orientation by asking
subjects to discriminate between a smooth surface and a grating (ridge
width, 1.5 mm; groove width, 0.75 mm). They were able to discriminate
the two surfaces when the axis of the grooves was parallel to the skin
ridges, but performance was below threshold in the orthogonal
orientation. The underlying neural mechanisms were investigated using
the gap stimuli to activate single slowly adapting type I
mechanoreceptive afferents (SAIs) innervating the fingerpads of
anesthetized monkeys. The edges of the gap produced response peaks, and
the gap resulted in a trough in the receptive field profiles. The
response magnitude at the peaks was greater, and at the troughs was
smaller, for larger gap widths and also when the axis of the gap was
parallel to the skin ridges as compared with the orthogonal
orientation. Simulated SAI population responses showed that response
profiles were distorted by variation in afferent sensitivity and by
neural noise. Using signal detection theory, based on a neural measure of the gaps computed over the active population, the acuity of the SAIs
under realistic population conditions was compared with human
performance. These analyses showed how parameters like afferent sensitivity, the pattern and density of innervation, and noise impact
on performance and why their impact is different for the two stimulus
orientations investigated. The greatest limitation was imposed by noise
that is independent of response magnitude, and this effect was greater
for stimuli oriented orthogonal to the skin ridges than for the
parallel orientation. |
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Bibliography: | ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23 |
ISSN: | 0022-3077 1522-1598 |
DOI: | 10.1152/jn.2000.84.3.1430 |