A timeline of preparatory activity prior to response initiation: Evidence from startle


In simple reaction time (RT) tasks, movement preparation can be modelled as an increase in neural activation to a sub-threshold level, with maintenance of this level until the go-signal. However, the absolute time requirement for response preparation following a warning signal (WS) is currently unknown, as tasks typically provide long foreperiods to ensure maximal preparation. The purpose of the present experiment was to determine the minimum length of time required to prepare a response. To probe the preparatory state of the motor response a startling acoustic stimulus (SAS) was used, as it has been shown to cause the involuntary early initiation of sufficiently prepared movements. Participants (n=17) completed 150 trials of a simple RT task requiring targeted wrist extension. A short (500ms) fixed foreperiod between the WS and go-signal was used to force rapid preparation of the response, whereas a long (8.5-10.5s) inter-trial interval was used to discourage a continual high state of preparation. A SAS was randomly presented on 30 trials at one of six time points: 0, 100, 200, 300, 400, or 500ms following the WS. Results showed that the proportion of startle trials where the intended response was elicited at short latency (<150ms following the SAS) was significantly lower when the SAS was presented simultaneous with the WS or 100ms later, as compared to 400ms after the WS or at the go-signal. These results suggest that a minimum of 200-300ms are required for responses to be sufficiently prepared to be triggered by a SAS.

Acknowledgments: Supported by NSERC and the Ontario Ministry of Research and Innovation