Abstract:
The aim of this study is to measure the thresholds of the Non-Pacinian I (NP I)channel which is believed to be mediated by rapidly-adapting (RA) fibers. Thresholds of the NP I channel were measured using a two-interval forced choice paradigm, a techniqueindependent of the subject̕s criterion. The experiments were performed using the terminalphalanx of the human middle finger with a 40Hz vibratory stimulus, but without using acontactor surround in order to enable comparison with population models ofmechanoreceptive fibers in the literature. Since the Pacinian (P) channel and NP I channelhave similar vibrotactile thresholds at 40Hz, a forward-masking procedure was used toelevate the thresholds of the P channel with respect to the NP I channel. By this procedureP channel can be perceptually masked using a 250Hz stimulus presented prior to the 40Hz test stimulus.In this study the masking functions of subjects were found to be approximatelylinear on log-log axes and the threshold shifts were found to increase as the maskingstimuluslevels increased which indicates that the vibrations are perceived by the subjectsmore difficultly. The results confirm that the masking procedure is reliable and the NP Ichannel can be selectively activated at 40Hz. The results are compared and discussed inrelation to previous studies. The long-term objective of this research is to provide information for determining the thresholds of other psychophysical channels as well for the application of the samemethod in auditory and visual threshold measurements.|Keywords: NP I channel, Rapidly-adapting fiber, Meissner corpuscle, Forward masking.
