Abstract
The StartReact effect is a phenomenon whereby a prepared response is involuntarily initiated/triggered with dramatically shortened reaction time (RT) by an intense startling acoustic stimulus (SAS) that also elicits a startle reflex. Previous research has shown that when a low-intensity “prepulse” stimulus was presented shortly before the SAS, the startle reflex was attenuated (i.e., decreased probability and magnitude of sternocleidomastoid (SCM) activation), yet the RT facilitation versus control remained intact. However, a potential confound in these results is that data were not dichotomized based on the presence/absence of a startle reflex in SCM and only included for participants who “consistently” startled. The current study employed similar prepulse methods but included data from all participants, regardless of SCM activation or RT latency on SAS trials. Participants performed a simple RT task requiring a targeted wrist extension as soon as possible following a visual go-signal. On 25% of trials a 120dB SAS was presented, half of which included an 80dB prepulse tone, 100ms prior to the SAS. Results showed that the prepulse stimulus led to a decrease in the probability and magnitude of the startle reflex, replicating previous studies. Notably, when a startle reflex was observed, RT was significantly shorter than when no reflex was observed, irrespective of whether a prepulse preceded the SAS or not. These results support previous studies indicating that a startle reflex in SCM is a valid and robust indication of whether a StartReact response is elicited, and extend this relationship to include prepulse paradigms.
