Abstract
The ability to perceive a tactile stimulus is reduced in a moving limb. This sensory attenuation effect, termed tactile suppression, is attributed to movement-related gating that allows the central nervous system to selectively process sensory information. However, the origin of this gating is debated, with some accounts implicating a forward-model, and others attributing the effect to backward-masking from peripheral reafference. The present study investigated the role of voluntary response initiation processes in tactile suppression by employing a startling acoustic stimulus (SAS) to trigger the early release of a planned movement independent of voluntary mechanisms. A forward-model account would predict that the timing of the suppression would be related to the expected time of voluntary initiation of the response, whereas a reafference account would predict that the suppression is linked directly to the timing of the motor act. Participants (n=10) performed a simple reaction time task requiring lifting the hand off a switch as quickly as possible following an auditory Go-signal, which was occasionally replaced with a 120dB SAS. A near-threshold electrical stimulus was applied to the moving hand at various time-points (50-170ms) after the Go-signal and participants reported whether they detected it. Preliminary results revealed detection rate was significantly lower for SAS trials at all stimulation times, suggesting that suppression does not depend on voluntary initiation but is linked to the production of the motor response. Moreover, detection rate was significantly lower on SAS trials even when time-locked to movement onset, suggesting that SAS may have further impeded sensory processing.
