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Relationships between touch sensations and estimated population responses of peripheral afferent mechanoreceptors

Relationships between touch sensations and estimated population responses of peripheral afferent... 221 94 94 1 1 Richard H. Cohen Charles J. Vierck Jr. Department of Neuroscience and Center for Neurobiological Sciences College of Medicine, University of Florida 32610-0244 Gainesville FL USA Abstract Trapezoidal indentations of the skin by a 0.5mm-diameter probe were presented at different rates and loads (forces) to the human fingertip, in order to compare estimates of population responses of cutaneous mechanoreceptors with the quality and magnitude of tactile sensations. The subjects were first trained to attend to and evaluate variations in the magnitude of touch sensations associated with the onset ramp, the plateau period, and the offset ramp. They examined a series of line drawngs that illustrated a variety of temporal profiles for sensation magnitude. The line drawings provided a straightforward means of describing temporal fluctuations of sensation intensity, which corresponded well to psychophysical ratios that were determined subsequently with a matching procedure. Influences of ramp rate on qualities of touch sensations were evaluated by tabulating verbal descriptions of sensory experiences. Each of three rate conditions generated a different quality of sensation during the dynamic portions of stimulation. Onsets and offsets at 100 g/s were described as “taps”. During ramps at 10 g/s the quality was described as “rolling” or “moving”. At 1 g/s no sense of motion was detected; instead, a “pressure” sensation was identified. Touch sensations during the plateau were always described as a pressure. The subjective magnitudes of touch sensations associated with the onset, plateau, and offset were equated by comparing different components of paired stimuli. At 100 g/s, when subjects matched the offset sensation from the first of a pair of stimuli with the onset sensation from the second, the force of the stimulus producing the offset sensation was 1.3 times greater than the intensity of the stimulus that produced the onset sensation. Matching of the plateau sensation (evaluated during the last 1.5 s of the 2.5-s plateau period) with the onset sensation required a plateau stimulus that was 1.7 times greater in force than the stimulus which produced the onset. Comparison of stimulus intensities producing a match of plateau and offset sensations with stimulus intensities predicted from the previous matches (onset versus offset and onset versus plateau) demonstrated a mean within-subject error of 4%. The mean ratio of plateau to offset forces that produced a match was 1.8∶1.3. In a matching procedure in which subjects compared the subjective magnitudes of plateau sensations following onset ramps of different rates, onset ramp rate significantly influenced the magnitude of pressure sensations. The ratios of plateau forces which produced equal magnitudes of sensation following 1,10, and 100 g/s ramps were 1.6∶1.3∶1.0. Psychophysical ratios of dynamic to plateau magnitudes of sensation were considerably discrepant with ratios of dynamic to plateau discharge of afferents supplying the glabrous skin of monkeys. Ratios of onset to plateau to offset sensation magnitude were 1.7∶1.0∶1.3 for trapezoidal presentations of 2 g of force at 100 g/s. Using the same stimulus conditions (Cohen and Vierck 1993), the corresponding values for estimates of the population discharge from rapidly adapting (RA) and slowly adapting (SA) afferents supplying the fingertip were 40.8∶1∶19.4. The onset to plateau ratio for the population response of type ISA (SAI) afferents (5.6∶1) was also substantially larger than the corresponding psychophysical ratio. The influence of ramp rate on the magnitude of the plateau sensations also did not correspond with neural responses. The discharge rate of SAI afferents during the last 1.5 s of the 2.5-s plateau periods was independent of ramp rate (Cohen and Vierck 1993). However, psychophysical ratios of 1.6∶1.3∶1.0 for the magnitudes of plateau sensations following ramp rates of 100, 10, and 1 g/s were discrepant with the neural ratios of 1.0∶1.0∶1.0. Temporal filtering from perceptual processing is not sufficient to account for the discrepancies between neural and psychophysical ratios. Therefore, the discharge from quickly and SA afferents must not combine linearly to determine sensation magnitude. The intensity of the tap sensation appears to be coded in a different way from pressure sensations; for the tap sensation the intensive code could be the number of active fibers, and the intensive code for pressure could be discharge rate among SA afferents. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Experimental Brain Research Springer Journals

Relationships between touch sensations and estimated population responses of peripheral afferent mechanoreceptors

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Publisher
Springer Journals
Copyright
Copyright © 1993 by Springer-Verlag
Subject
Biomedicine; Neurosciences; Neurology
ISSN
0014-4819
eISSN
1432-1106
DOI
10.1007/BF00230475
Publisher site
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Abstract

221 94 94 1 1 Richard H. Cohen Charles J. Vierck Jr. Department of Neuroscience and Center for Neurobiological Sciences College of Medicine, University of Florida 32610-0244 Gainesville FL USA Abstract Trapezoidal indentations of the skin by a 0.5mm-diameter probe were presented at different rates and loads (forces) to the human fingertip, in order to compare estimates of population responses of cutaneous mechanoreceptors with the quality and magnitude of tactile sensations. The subjects were first trained to attend to and evaluate variations in the magnitude of touch sensations associated with the onset ramp, the plateau period, and the offset ramp. They examined a series of line drawngs that illustrated a variety of temporal profiles for sensation magnitude. The line drawings provided a straightforward means of describing temporal fluctuations of sensation intensity, which corresponded well to psychophysical ratios that were determined subsequently with a matching procedure. Influences of ramp rate on qualities of touch sensations were evaluated by tabulating verbal descriptions of sensory experiences. Each of three rate conditions generated a different quality of sensation during the dynamic portions of stimulation. Onsets and offsets at 100 g/s were described as “taps”. During ramps at 10 g/s the quality was described as “rolling” or “moving”. At 1 g/s no sense of motion was detected; instead, a “pressure” sensation was identified. Touch sensations during the plateau were always described as a pressure. The subjective magnitudes of touch sensations associated with the onset, plateau, and offset were equated by comparing different components of paired stimuli. At 100 g/s, when subjects matched the offset sensation from the first of a pair of stimuli with the onset sensation from the second, the force of the stimulus producing the offset sensation was 1.3 times greater than the intensity of the stimulus that produced the onset sensation. Matching of the plateau sensation (evaluated during the last 1.5 s of the 2.5-s plateau period) with the onset sensation required a plateau stimulus that was 1.7 times greater in force than the stimulus which produced the onset. Comparison of stimulus intensities producing a match of plateau and offset sensations with stimulus intensities predicted from the previous matches (onset versus offset and onset versus plateau) demonstrated a mean within-subject error of 4%. The mean ratio of plateau to offset forces that produced a match was 1.8∶1.3. In a matching procedure in which subjects compared the subjective magnitudes of plateau sensations following onset ramps of different rates, onset ramp rate significantly influenced the magnitude of pressure sensations. The ratios of plateau forces which produced equal magnitudes of sensation following 1,10, and 100 g/s ramps were 1.6∶1.3∶1.0. Psychophysical ratios of dynamic to plateau magnitudes of sensation were considerably discrepant with ratios of dynamic to plateau discharge of afferents supplying the glabrous skin of monkeys. Ratios of onset to plateau to offset sensation magnitude were 1.7∶1.0∶1.3 for trapezoidal presentations of 2 g of force at 100 g/s. Using the same stimulus conditions (Cohen and Vierck 1993), the corresponding values for estimates of the population discharge from rapidly adapting (RA) and slowly adapting (SA) afferents supplying the fingertip were 40.8∶1∶19.4. The onset to plateau ratio for the population response of type ISA (SAI) afferents (5.6∶1) was also substantially larger than the corresponding psychophysical ratio. The influence of ramp rate on the magnitude of the plateau sensations also did not correspond with neural responses. The discharge rate of SAI afferents during the last 1.5 s of the 2.5-s plateau periods was independent of ramp rate (Cohen and Vierck 1993). However, psychophysical ratios of 1.6∶1.3∶1.0 for the magnitudes of plateau sensations following ramp rates of 100, 10, and 1 g/s were discrepant with the neural ratios of 1.0∶1.0∶1.0. Temporal filtering from perceptual processing is not sufficient to account for the discrepancies between neural and psychophysical ratios. Therefore, the discharge from quickly and SA afferents must not combine linearly to determine sensation magnitude. The intensity of the tap sensation appears to be coded in a different way from pressure sensations; for the tap sensation the intensive code could be the number of active fibers, and the intensive code for pressure could be discharge rate among SA afferents.

Journal

Experimental Brain Research – Springer Journals

Published: May 1, 1993

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