Abstract
How does one switch from a reactive to a proactive/intentional response mode? An annular ‘gauge’ fills in within time T. Subjects must press a button in synchrony with the completion of the filling in. Equivalently, they have to press a button in synchrony with the last of a series of 3 equally paced light-flashes (pairs of Gaussian blobs displayed so as to form a hexagon) of period T. T is random across trials (from 0 to 500 ms). Response Time (RsT) - measured from the onset of the gauge or of the second event in the sequence of 3 - is T-independent up to E = RsT(T=0)+K and equals T thereafter. E is the ‘elbow’ of the RsT(T) function. It reflects the timing of the operations performed for deciding to switch from the reactive to the proactive response mode including subjects' introspective estimation of their Reaction Time, RT (assessed in independent experiments) to the gauge and to the 3-events stimuli. RsT(T=0) is RsT at T = 0 and is about 70 and 16 ms longer than the RT to these two stimulations, respectively. K ≈ 30 ms in both experiments. Based on a simple sequential processing model, these data allow the inference of the ‘time-to-impact’/velocity computation (in the gauge experiment; ≈ 60 ms), the bias of the introspective RT estimation (≈ +30 ms) and the decision time to switch from the reactive to the intentional response mode (≈ 20 ms). This paradigm unveils the introspective nature of deciding between re-acting and postponing action.