PRACTICE-RELATED IMPROVEMENTS IN SOMATOSENSORY INTERVAL DISCRIMINATION ARE TEMPORALLY SPECIFIC BUT GENERALIZE ACROSS SKIN LOCATION, HEMISPHERE, AND MODALITY

This paper concerns the characterization of performance and perceptual learning of somatosensory interval discrimination. The purposes of th is study were to define (1) the performance characteristics for interv al discrimination in the somatosensory system by naive adult humans, ( 2) the normal capacities for improvement in somatosensory interval dis crimination, and (3) the extent of generalization of interval discrimi nation learning. In a two-alternative forced choice procedure, subject s were presented with two pairs of vibratory pulses. One pair was sepa rated in time by a fixed base interval; a second pair was separated by a target interval that was always longer than the base interval. Subj ects indicated which pair was separated by the target interval. The le ngth of the target interval was varied adaptively to determine discrim ination thresholds. After initial determination of naive abilities, su bjects were trained for 900 trials per day at base intervals of either 75 or 125 msec for 10-15 d. Significant improvements in thresholds re sulted from training. Learning at the trained base interval generalize d completely across untrained skin locations on the trained hand and t o the corresponding untrained skin location in the contralateral hand. The learning partially generalized to untrained base intervals simila r to the trained one, but not to more distant base intervals. Learning with somatosensory stimuli generalized to auditory stimuli presented at comparable base intervals. These results demonstrate temporal speci ficity in somatosensory interval discrimination learning that generali zes across skin location, hemisphere, and modality.