Meta-analysis of startle data confirms sex differences in simple reaction time are not due to response preparation levels


Simple reaction time (RT) can vary by sex, with males generally displaying faster RTs. Although several explanations have been offered, the possibility that motor preparation differences may underlie the effect of sex on simple RT has not yet been explored. A startling acoustic stimulus (SAS), which can involuntarily trigger a prepared motor response (i.e., StartReact effect) can be used to assess response preparation by comparing RT on SAS trials to that in control/voluntarily initiated trials, as well as through the proportion of trials demonstrating startle-reflex EMG activity in the sternocleidomastoid (SCM) muscle. The present study examined sex-differences in motor preparation, using data obtained from 27 studies published between 2006-2019. Linear mixed effects models were conducted to assess the effect of sex on control and SAS RT as well as the proportion of SAS trials with SCM activation. Results indicated that females displayed significantly larger RT differences between SAS and control trials (P=.025). This interaction was due to a significantly slower control trial RT in female participants as compared to males (P=.026), but no significant sex differences in SAS RT (P=.309). Additionally, no significant effect of sex on the proportion of startle reflex activity was observed (P=.243). These results confirm previously demonstrated sex differences in simple RT during voluntary initiation but indicate that these sex differences are not explained by varying levels of response preparation, as evidenced by the lack of sex-dependence in the StartReact effect measures. Instead, it is likely that these differences arise from processes related to response initiation.