Dissociating premotor and motor components of response times: Evidence of independent decisional effects during motor-response execution

Traditional measures of response times (RTs) capture the summed duration of multiple latent and overt processes, including motor-response execution. The present research assessed the functional independence of the decisional components unfolding before vs after the onset of the muscular activation in the context of a lexical decision task requiring manual button-press responses. Specifically, the lexicality effect (slower latencies for nonwords compared to words) was separately tracked across premotor and motor components of RTs under different regimes of decision bias. Whereas at the premotor level the lexicality effect was modulated by the proportion of word vs nonword trials in the block, with a reversal of the lexicality phenomenon when nonwords occurred in 75% of the trials, motor times (i.e., a chronometric measure of response duration) consistently displayed longer durations for nonword responses, irrespective of bias manipulation. The results point to a partial functional independence between the decisional components involved at the premotor vs motor level, suggesting that the onset of motor behavior may represent the onset of specific decisional processes, rather than the termination or the continuation of computations unfolding in the premotor interval.