Discrimination of Simulated Texture Patterns on the Human Hand.
Kops, Carolyn E. and Esther P. Gardner.
Department of Physiology and Neuroscience, New York University School of
Medicine, 550 First Avenue, New York, NY 10016, USA.
APStracts 3:0054N, 1996.
SUMMARY AND CONCLUSIONS
1. Textures formed by periodic dot arrays are defined by the dot density,
spacing and angular orientation with respect to the direction of motion. In
this report we evaluate the effects of the dot density (intensive cues) and
arrangement (spatial cues) upon the ability of human subjects to discriminate
texture patterns scanned across an OPTACON tactile stimulator that selective
stimulates rapidly-adapting cutaneous mechanoreceptors. We compared dot arrays
arranged on the index finger in specific patterns (horizontal, vertical,
diamond, up diagonal or down diagonal orientation) and spaced 4.8, 7.2 or 9.6
mm apart (high, medium and low density) using a two-alternative forced-choice
protocol. 2. Textures are well discriminated when their elements are tightly
spaced along one axis, and widely spaced upon all other axes. Humans
distinguish textures that differ only in orientation with mean accuracy of 75%
at low density, and 65% at medium density, but discriminate high density
textures poorly (mean accuracy = 48%). Accuracy is related to the angular
disparity between patterns, and to similarity of spacing and orientation along
major and minor axes of the arrays. Vertical and horizontal patterns are more
accurately distinguished than the oblique ones, and diamond arrays are the
least well discriminated. Diagonal and diamond textures are often confounded,
and the up and down diagonal patterns are confused with each other
particularly as the texture density rises. The preference for the vertical and
horizontal patterns may relate to an interaction between the orientation axis
of the texture and its direction of motion across the skin. 3. Intensive cues
provided by the total number of applied stimuli supplement the spatial cues
inherent to the pattern orientation, as textures that differ in both spacing
and orientation are discriminated better than those that differ only in
orientation or spacing. Mean accuracy ranges from 96% for comparisons of high
and low density textures, which differ in the total number of dots by a factor
of two, to 80% when medium density patterns are compared to high or low
density textures. 4. Textures that differ in density but not in orientation
are less well discriminated than those of different orientation. For example,
82% of patterns that differ in both density and orientation are distinguished
correctly in pairings of low and medium density textures, while those that
differ only in density are discriminated correctly on 45% of trials. Subjects
seem to use spatial rather than intensive cues when discriminating patterns of
similar density, suggesting that the similarity of form (the spatial
arrangement of the closely spaced dots) is more readily apparent than small
differences in spacing along the axis of motion. 5. Subjects are most most
successful in differentiating texture patterns when they are able to mentally
picture the orientation and spacing of the pattern. We found a strong
correlation between their ability to discriminate textures of a given spacing
and their ability to identify the specific texture by matching it to the
appropriate visual representation. Subjects are able to identify correctly all
five orientations at low and medium densities, with mean accuracy of 76%, but
recognize only the vertical arrays when high density patterns are presented.
The ability to image the textures is noteworthy, as subjects received no
feedback about performance. 6. Spatial imaging of textures appears limited by
the diameter of cutaneous receptive fields on the hand. We propose that the
structural axis of a regular texture array results from perceptual linkage of
adjacent elements along one principal axis by continuous bands of neural
activity when their spacing is smaller than the receptive field diameter.
Spacing along opponent axes must be wider than the field diameter for the
pattern to be discriminated, as the neural populations activated by the
closely spaced dots are separated along the orthogonal axis by silent groups
of afferents with no active texture elements within their receptive fields.
Received 27 July 1995; accepted in final form 7 March 1996.
APS Manuscript Number J487-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 27 March 96