Summary
The human capacity to scale the intensity of brief mechanical indentations of the hairy skin was measured by the method of subjective magnitude estimation. The afferent discharges evoked by nearly identical stimuli delivered to comparable locations on the hairy skin in monkeys were recorded in a number of types of first-order mechanoreceptive afferents. It was shown that of these only those which adapt slowly to mechanical stimuli possess sufficient dynamic range of response to account for the range of human pressure sensation. Two such afferents innervating the hairy skin, previously identified by others as the Type I and Type II afferents, were studied in detail as regards their responses to brief mechanical stimuli of different intensities.
The relation of the human subject's estimate of intensity to stimulus magnitude is described by a power function with an exponent of about 0.4. Using impulse frequency in the “early steady state” as a measure, the responses of both types of slowly adapting mechanoreceptive afferents are related to stimulus magnitudes by power functions with exponents averaging about 0.5. On the assumption that the stimuli used elicit similar patterns of discharge in the first-order afferents innervating the hairy skin of men and monkeys, the results support the general proposition, now shown to hold for a number of senses, that the intensity of human sensation is determined by the functional properties of the first-order sensory fibers, and that the final behavioral output in the form of a subjective estimate of magnitude is a linear function of the frequency of discharge in those first-order fibers.
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Supported in part by training and research grants from the United States Public Health Services, No's 1-PO1-NB-06828, TO1-GM-00443, and 5-TO1-NB-0523.
The research described in this paper was submitted by Dr. Merzenich in partial fulfilment of the requirements for the degree of Doctor of Philosophy, The Johns Hopkins University, June, 1968.
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Harrington, T., Merzenich, M.M. Neural coding in the sense of touch: Human sensations of skin indentation compared with the responses of slowly adapting mechanoreceptive afferents innervating the hairy skin of monkeys. Exp Brain Res 10, 251–264 (1970). https://doi.org/10.1007/BF00235049
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DOI: https://doi.org/10.1007/BF00235049