AbstractThe purpose of the current study was to examine the processes involved in the preparation of timing during response initiation and execution through the use of a startling acoustic stimulus (SAS). Participants (N=13) performed a delayed-response task in which a two key-press movement was to be initiated 200 ms after an imperative signal (IS) with either a short (200 ms) or long (500 ms) interval between key-presses. On selected trials, a SAS was presented to probe the preparation processes associated with the initiation delay and execution of the inter-key interval. The SAS resulted in a significant decrease in the initiation time (p < .001), which was attributed to a speeding of pacemaker pulses used to time the delay interval, caused by an increased activation due to the SAS. Conversely, the SAS significantly increased the short inter-key interval (p = .040), which was attributed to temporary interference with cortical processing. Collectively, these results support a different timeline for the preparation of the delay interval, which is thought to be prepared in advance of the IS, and the inter-key interval, which is thought to be prepared following the IS. This conclusion provides novel information with regards to timing preparation that is consistent with models in which response preparation, initiation, and execution are considered separate and dissociable processes.
Acknowledgments: Supported by the Natural Sciences and Engineering Research Council of Canada (NSERC).