Research report
Some characteristics of tactile channels

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Abstract

The four information-processing channels of glabrous skin have distinct tuning characteristics which appear to be determined in the periphery at the level of sensory receptors and their afferent nerve fibers. The four-channel model [J Acoust Soc Am 84 (1988) 1680] has been updated to include measurement over a wider frequency range of tuning of the P and NP I channels, psychophysically determined by forward-masking and adaptation tuning curve methods. In addition to differences in their tuning, the P and NP channels differ in the following ways: (1) the P channel, but not NP channels, has been found to be capable of temporal summation, which operates by neural integration; (2) the capacity for spatial summation is also an exclusive property of the P channel; (3) sensitivity declines with age at a greater rate in the P channel than in the NP channels; (4) the masking or adaptation of a channel has no effect on the sensitivity of the other channels, although the channels interact in the summation of the perceived magnitudes of stimuli presented to separate channels.

Introduction

Fundamental to understanding the properties of sensory systems is the concept of the information-processing channel. A channel is an element that is tuned to a specific region of the energy spectrum to which the system responds. Channels have been discovered in the sense of touch as well as in other modalities [25]. In a multichannel sensory system, different channels, tuned to different regions of the spectrum, provide information about the relative energy levels in various parts of the spectrum representing a particular stimulus. According to this approach, qualitative and quantitative dimensions of perceptual experience are determined by the relative activity levels in each of several channels (see [2]).

Section snippets

The tuning of tactile channels

When all but the smallest contactors are used to stimulate glabrous [21] or hairy (e.g. [23]) skin, vibrotactile thresholds are a U-shaped function of stimulus frequency with the lowest values at approximately 250–300 Hz. In addition, it has been demonstrated that this threshold function becomes relatively flat at low frequencies. The change in the slope of the function at low frequencies was interpreted by Békésy [1] as evidence that separate mechanisms mediate the detection of low and high

Temporal and spatial summation

Verrillo [22] found that when a 250-Hz stimulus delivered through a large 2.9 cm2 contactor to the thenar eminence excites Pacinian corpuscles, the detection threshold decreases as stimulus duration increases up to a duration of about 1.0 s. However, when the same stimuli are applied through a small 0.01 cm2 contactor, incapable of exciting the P channel but capable of exciting the NP II channel, the detection threshold is independent of stimulus duration. These results indicate that the P channel

The effects of aging in the sensitivity of tactile channels

The most interesting aspect of the finding that the sense of touch, like other sensory systems, suffers from the deleterious effects of aging is that the rate at which tactile sensitivity declines with age is not the same in each of the tactile channels. This is clearly seen in the results presented in Fig. 6 in which the average detection threshold on the thenar eminence is plotted as a function of the average age of eight groups of observers. The sensitivities of the P, NP I, and NP III

Channel interactions

Clearly, the results of psychophysical and neurophysiological studies have determined that separate information-processing channels, each with its own physiological mechanism, the origin of which lies in specific receptors and peripheral nerve fibers, exist for the perception of tactile stimuli. However, fundamental questions remain concerning the nature of how these channels, with their individual properties, operate together in the perception of tactile stimuli encountered in the natural

Acknowledgements

This work was supported in part by funds from grants NIH, P01DC00380 and NIH, R01NS-38661 from the National Institutes of Health.

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