A startling acoustic stimulus interferes with upcoming motor preparation: Evidence for a startle refractory period


Previous work has shown that when a loud, startling acoustic stimulus (SAS) is used in a simple reaction time (RT) task, response latency is significantly shortened (Valls-Solé et al. 1999). The present study used a SAS in a psychological refractory period (PRP) paradigm to determine if the RT1 “savings” would be inherited by RT2, as propagation effects are predicted by the serial processing model of dual-task processing. Participants (n=12) performed a simple reaction time paradigm in which they reacted to an auditory stimulus (S1) with a vocal response (R1) followed by a visual stimulus (S2) to which they performed a key-lift task (R2). The two stimuli were separated by a stimulus onset asynchrony (SOA) of either 100 ms, 200 ms, 500 ms, 1000 ms or 1500 ms. On selected trials S1 was replaced with a 124 dB SAS, which triggered R1 40-50 ms earlier than non-startle trials. Although a typical PRP effect was found for both startle and non-startle trials, the results indicated that rather than the predicted propagation of RT, significantly longer responses were found for RT2 on startle trials at the 100 ms and 200 ms SOA conditions. These results can be attributed to the startling stimulus interfering with cognitive processing and thus delaying the preparation and/or execution of the second response. This interference or “startle refractory period” is in addition to the typical psychological refractory period associated with limitations in the preparation of two responses simultaneously.

Acknowledgments: This research was supported by separate Natural Sciences and Engineering Research Council of Canada grants awarded to Romeo Chua and Ian M. Franks