PERCEPTION OF VIBROTACTILE STIMULI DURING MOTOR-ACTIVITY IN HUMAN-SUBJECTS

Previous studies have shown that voluntary motor activity decreases th e ability to detect near-threshold electrical stimuli applied to the s kin, but has no effect on the perception of either suprathreshold elec trical stimuli or natural thermal stimuli (warmth, heat pain). The pre sent study was undertaken to determine if the perception of natural ta ctile stimuli (vibrotactile) is diminished by motor activity (rhythmic al isometric flexions and extensions about the elbow). The stimuli wer e applied at three different sites on the operant arm ventral forearm, thenar eminence and distal digit - to examine also the influence of t he proximity of the stimulated site to the active muscles on perceptio n. The ability to detect near-threshold stimuli at the two more proxim al stimulation sites was significantly reduced during the motor task, and these effects were more pronounced and widespread with higher leve ls of target force (20 N vs 50 N). Discrimination of small differences in the intensity of suprathreshold stimuli, at all three sites, was u nchanged during the motor task. Finally, the subjective intensity of s uprathreshold vibrotactile stimuli was reduced, in a nonlinear fashion , during the motor task; proximity again influenced the degree of modu lation. In contrast a previous study showed no change in magnitude est imates of suprathreshold electrical stimuli during isotonic flexion an d extension. Some possible reasons for the discrepancy are discussed. In addition, our previous suggestion that movement produces a simple r eduction in the signal-to-noise ratio (i.e. the gating signal modelled as a masking stimulus) cannot explain the present results, so more co mplex models are required.