Stability of temporal resolution of the tactile sensory system for a one-year interim.

Abstract

The ability of the tactile sensory system to resolve time differences between successive pulses (threshold of fusion) depends not only on the physical properties of the stimulus but also on the characteristics of the observer. It has previously been demonstrated that subjects' training and level of sophistication can influence tactile fusion thresholds. but the stability of the fusion threshold has not yet been investigated (1). This study was done to provide information concerning the stability of tactile fusion thresholds over an extended period of time. The subjects were three adult males trained in psychophysical techniques. Detailed descriptions of the vibrotactile pulse-generation system and the critical fusion threshold procedure can be found elsewhere (2). Vibrotactile fusion thresholds were obtained from the anterior midline dorsal surface of the tongue and the thenar eminence of the right hand. The pulses generated were I-msec. square waves with the second sequentially generated pulse having a variable time of onset from the first pu!se. The pulses were presented at 15 dB sensation level. To obtain fusion thresholds, the two pulses were presented to the test structure starting with an interpulse interval of 40 msec. This interpulse interval was then decreased until a fusion point (the stimuli were perceived as one) was reached. When a fusion point was reached, the interpulse interval was increased until the subject reported the presence of two stimuli again. The test p:ocedure ended when four reversal points were obtained. The mean of the four reversals was accepted as the critical fusion threshold for each subject and test site. One year later, the same subjects were retested using identical experimental instrumentation methods and procedures. The mean fusion thresholds and standard deviations were 20.86 msec. and 0.45, respectively, for the tongue and 20.13 msec. and 1.40, respectively, for the hand. The mean fusion thresholds and standard deviations taken 1 yr. later were 20.70 msec. and 0.58, respectively, for the tongue and 19.20 msec. and 1.60, respectively, for the hand. No appreciable difference occurred in mean fusion thresholds or standard deviations for either test scrucrure over one year. These findings suggest that temporal resolution, as demonstrated by vibrotactile fusion threshold technique, remained stable over time for the tongue and thenar eminence of three normally functioning male adults. The stability shown by the fusion thresholds suggests that these thresholds may provide a sensitive index of the neurological integriry of both the oral and nonoral tactile sensory systems. Further research is warranted in which larger samples are utilized to assess the stability of tactile fusion thresholds.