Vibrotactile adaptation enhances amplitude discrimination.

Human psychophysical detection and amplitude discrimination thresholds for 25-Hz sinusoidal vibrations were measured on the thenar eminence using two-interval forced-choice tracking, in the unadapted state and following exposure to 25-Hz adapting stimuli representing a range of amplitudes (5-25 dB SL). As expected, detection threshold was elevated 6 to 7 dB for each 10-dB increase in the adapting stimulus. In contrast, amplitude difference thresholds for 10 and 20 dB SL standard stimuli were generally lowest when the amplitude of the adapting stimulus was equal to the amplitude of the standard. The results indicate that while adaptation impairs detection of a liminal vibrotactile stimulus, it improves intensity discrimination of supraliminal stimuli that are close in amplitude to the adapting stimulus. The compatability between these results and a recently proposed model of cortical dynamics (Whitsel et al., 1989) suggests that cortical events may contribute significantly to the physiological basis of vibrotactile adaptation.