Abstract
To sense the texture of a surface, we run our fingers across it, which leads to the elicitation of skin vibrations that depend both on the surface and on exploratory parameters, particularly scanning speed. The transduction and processing of these vibrations mediate the ability to discern fine surface features. The objective of the present study is to characterize the effect of changes in scanning speed on texture-elicited vibrations to better understand how the exploratory movements shape the neuronal representation of texture. To this end, we scanned a variety of textures across the fingertip of human participants at a variety of speeds (10–160 mm s−1) while measuring the resulting vibrations using a laser Doppler vibrometer. First, we found that the intensity of the vibrations—as indexed by root-mean-square velocity—increases with speed but that the skin displacement remains constant. Second, we found that the frequency composition of the vibrations shifts systematically to higher frequencies with increases in scanning speed. Finally, we show that the speed-dependent shift in frequency composition accounts for the speed-dependent change in intensity.
Highlights
To discern the texture of a surface, we spontaneously run our fingers across it [1], an exploratory procedure that results in the elicitation of skin vibrations that reflect the microstructure of the surface
While coarse textural features can be sensed without movement, our perception of fine textural features relies on the processing of skin vibrations elicited during scanning [2,3,4,5]
Using a custom-built rotating drum stimulator, we scanned eight textured surfaces across the right index fingertip of five human subjects at 28 speeds spanning the range used in natural texture exploration [12] while measuring the evoked skin vibrations using an laser Doppler vibrometer (LDV) (OFV-3001 with OFV 311 sensor head; Polytec, Irvine, CA)
Summary
To discern the texture of a surface, we spontaneously run our fingers across it [1], an exploratory procedure that results in the elicitation of skin vibrations that reflect the microstructure of the surface. Two populations of tactile nerve fibres—rapidly adapting (RA) and Pacinian (PC) fibres—are exquisitely sensitive to skin vibrations and produce millisecond-precision temporal spiking sequences that reflect the vibrations [3,4,6,7]. These vibration-sensitive afferents mediate our ability to perceive fine textural features as evidenced by the fact that desensitizing them impairs the perception of fine texture [5]. The firing rates of nerve fibres and of their downstream targets tend to increase with increases in scanning speed [9,10]. Whether this enhanced neural response reflects the contraction of the spike trains or is caused by an additional increase in the amplitude of the vibrations—which would lead to higher firing rates— remains to be elucidated
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