Effects of stimulus intensity on the habituation of flexor withdrawal activity mediated by the functionally transected human spinal cord

Abstract

Ten patients with a chronic, transverse lesion of the cervical spinal cord were submitted to two daily sessions involving a relatively high- or low-intensity habituating stimulus applied unilaterally to a midplantar site at the rate of 1/sec. Test stimuli of relatively high, intermediate, and low intensity were applied before and after habituation training. Response measures were based upon the integrated electromyographic activity of the tibialis anterior muscle. Analyses of both absolute and relative responses measures obtained during and at the termination of habituation training indicated that the degree of habituation was inversely related to the intensity of stimulation. The incremental growth in responsiveness observed during the first few repetitions of the habituating stimuli was greater for strong stimulation than for weak. Analyses of responses to test stimuli applied before and after habituating training suggested that the effects of the strong habituating stimulus generalized more to a posthabituation test stimulus of intermediate intensity than did the effects of the weak habituating stimulus. © 1977, Psychonomic Society, Inc.. All rights reserved.