Learning in tactile channels.

Vibrotactile intensity-discrimination thresholds for sinusoidal stimuli applied to the thenar eminence of the hand declined as a function of practice. However, improvement was confined to the tactile information-processing channel in which learning had occurred. Specifically, improvements in performance with training within the Pacinian-corpuscle (PC) channel with a 250-Hz stimulus failed to transfer to performance within the rapidly adapting (RA) nerve fiber channel and the slowly adapting Type I (SA I) nerve fiber channel with a 20-Hz stimulus; similarly, improvements in performance with training within the RA/SA I channels failed to transfer to the PC channel. The hypothesis that tactile intensity-discrimination learning involves changes in sensory processes rather than the acquisition of the general skills required to perform the intensity-discrimination task is supported by the finding that improvements in performance with practice did not transfer to the untrained contralateral hand and by the finding of no transfer of training across channels. Within the PC channel, improvements in intensity discrimination with training transferred from the training intensity level (20-dB SL) to an untrained intensity level (10-dB SL), showing that learning within the PC channel under a specific stimulus condition can generalize to another stimulus condition provided both stimuli are processed by the PC channel. The finding that intensity-discrimination training, which resulted in a substantial reduction in the intensity difference limen, had no effect on the slope of the sensation-magnitude function suggests that tactile intensity-discrimination learning results primarily from a progressive reduction in neural noise over the course of training.