Redefining the decisional components of motor responses: Evidence from lexical and object decision tasks

Models of decision making focusing on two-alternative choices have classically described motor-response execution as a nondecisional stage that serially follows the termination of decision processes. Recent evidence, however, points toward a more continuous transition between decision and motor processes. We investigated this transition in two lexical decisions and one object decision task. By recording the electromyographic (EMG) signal associated with the muscle responsible for the manual responses (i.e., button press), we partitioned single-trial reaction times into premotor (the time elapsing from stimulus onset until the onset of the EMG burst) and motor times (the time elapsing from the onset of the EMG burst and the button press), with the latter measuring response execution. Responses were slower for pseudowords and pseudo-objects compared to words and real objects. Importantly, these effects were reliable even at the level of motor time measures. Differently, despite the reliable effect at the level of reaction times and premotor times, there was no difference in motor times between high and low-frequency words. Although these results, in line with recent evidence, challenge a purely noncognitive characterization of motorresponse execution, they further suggest that motor times may selectively capture specific decisional components, which we identify with late-occurring verification and/or control mechanisms.