Observed temporal summation effects for lingual vibrotactile threshold measurements

Abstract

Investigations using mechanical stimulation to measure lingual threshold sensitivity have resulted in conflicting assumptions concerning the nature of underlying neural transducers. A basic question concerns whether or not exteroceptive touch receptors in the lingual surface summate energy in response to displacement of tissues. This study tested the hypothesis that these receptors would demonstrate temporal summation as a function of pulse duration time. The stimulus unit included an audio oscillator, frequency counter, electronic switch, interval timer, amplifier, and electromagnetic vibrator. The measurement unit consisted of an accelerometer, cathode follower, microphone amplifier, and vacuum‐tube volt‐meter. Vibrotactile lingual thresholds for 250 Hz were obtained for four groups of normal speaking adult subjects using respective pulse duration times of 50, 100, 200, and 400 msec. Peak values were recorded in millivolts and converted to dB re one micron rms. Temporal summation was observed up to 200 msec reaching an asymptote around 400 msec. Findings supported the position that tactile transducers in mucous tissues respond to vibratory displacements in the same ways as pressure receptors in other cutaneous tissues.