Inhibition of motor-related activation during a simple reaction time task requiring visuomotor mental rotation

The present study investigated whether differences in reaction time (RT) between movements initiated to a visual cue (directly cued) versus movements initiated to a location other than the visual cue (indirectly cued) arise because of varying levels of inhibition within the motor system during response preparation. Unlike typical visuomotor mental rotation (VMR) experiments, this study employed a simple RT paradigm to allow response preparation to occur in advance of the imperative stimulus (IS). Participants responded to the IS by either moving directly to the location of a visual cue or to a location that required a mental transformation between the visual cue and the intended movement goal (i.e., a location 60, 90, or 120 degrees rotated with respect to the visual cue). To probe motor-related activation during response preparation, a startling acoustic stimulus (SAS, 124 dB) was randomly presented 500 ms, 1,000 ms, or 1,500 ms after visual cue onset, but before the IS. Results showed similar RTs during nonstartle control trials regardless of rotation angle and whether trials were completed in a random or blocked design. Additionally, SAS trials showed a low incidence of early response triggering across all time points regardless of whether the movement was directly or indirectly cued. In contrast, directly cued movements performed outside of the VMR context showed a high incidence of SAS response triggering. These results suggest that when a stimulus to target-goal transformation might be required, inhibitory suppression of motor-related activation arises regardless of whether the final movement is directly or indirectly cued.