Electrotactile Sensitivity under Different Intensities of Simultaneous Auditory Stimulation

Direct electrical stimulation of the skin can arouse sensations similar to those from brief mechanical contact. In this study, tactile thresholds were obtained with brief pulses of direct current, under four different intensities of simultaneous broad‐band continuous noise ranging from 54 dB (estimated ambient noise) to 92 dB SL. Stimulation site was the right thenar eminence, the palmar base of the thumb. Electrical touch stimuli were 100‐msec‐long trains of 0.5‐msec anodal rectangular pulses, delivered by constant current stimulator at a pulse repetition rate of 100 pps. Thresholds were obtained from 12 subjects by means of a two‐alternative forced‐choice procedure. Stimulus intensity was varied by changing pulse amplitude alone. Electrotactile thresholds were highest under moderately intense noise, 66 and 79 dB SL. The magnitude of the threshold shift was small, less than 1.0 (tactile) dB, and statistically significant. Thresholds were lowest at both extremes of the sound intensity range, 54 and 92 dB SL. Variability around threshold was greatest under moderate intensity noise, least under ambient noise, where tactile thresholds were lowest. Electrotactile intensity discrimination, as it presumably involves stimulation behind the receptor, should measure limits for the touch sense. ΔI/I was most acute where absolute thresholds were worst, under moderate noise intensity. Conservative estimates of ΔI/I using run length are at worst 0.05/with ambient noise, a value in line with vibratory tactile measures.