Perception of timing of movement-onset in a simple reaction time task

Subjects judged verbally on temporal order between pressing a switch and a marking sound (MS) in a simple reaction time paradigm. They were uncertain when sound preceded movement by less than about 60 ms or followed it by less than 130 ms (transient zone--TZ). The point of subjective equality (defined by 0.5 probability of correct judgements of temporal order of sound and switching onsets) and the median of TZ were shifted about 60 and 35 ms prior movement onset, respectively. Estimating mutual timing of movement preparation and execution and sensory delays, these shifts correspond to the simultaneity of onsets of MS and proprioceptive feedback in the brain. Thus the results suggest about proprioceptive origin of perception of active movement onset.