Tactile suppression is linked to movement onset for startle-triggered responses

The ability to perceive a tactile stimulus is reduced in a moving limb, a phenomenon known as tactile suppression. This sensory attenuation effect is attributed to movement-related gating, which allows the central nervous system to selectively process sensory information. However, the source of this gating is uncertain, with some evidence suggesting a forward-model origin of tactile suppression, and other evidence in support of backward masking from peripheral reafference. This study investigated the contribution of these mechanisms to tactile suppression by employing a startling acoustic stimulus (SAS) to involuntarily trigger the early release of a planned movement. A forward-model account would predict that the timing of the suppression would align with the anticipated time of voluntary response initiation, whereas a reafference account would predict that suppression timing would be linked directly to the actual time of the motor act. Participants (n = 27) performed a simple reaction time task involving a rapid wrist extension to release a switch in response to an auditory go-signal, which was occasionally replaced with a 120 dB SAS. On each trial, participants reported whether they detected a near-threshold electrical stimulus applied to the moving hand at various times (50-170ms; 30 ms steps) after the go-signal. Results showed a significantly lower detection rate on SAS trials at all stimulation times (p < .001), supporting the proposition that suppression does not depend on the predicted timing of voluntary initiation, but rather is linked to the production of the motor response. Furthermore, detection rate was significantly lower on SAS trials even when time-locked to movement onset, suggesting that the SAS may have further impeded sensory processing (p < .001).