Bisecting RT with lateralized readiness potentials: Precue effects after LRP onset

Recent work has sought to use the time at which the Lateralized Readiness Potential (LRP) first develops (LRP onset) as a temporal landmark to bisect experimental effects on reaction time (RT). Many studies have found experimental effects on the time between the signal and LRP onset, but few have found effects on the time between LRP onset and RT (LRP-RT interval). The primary goal of this study was to produce an effect on the LRP-RT interval. We employed precuing, a manipulation likely to influence motor-programming processes at the end of the RT interval. Subjects performed a 4-alternative choice-RT task in which a signal prompted a button-press with the index or middle finger on the left or right hand. Precues preceded the signals and were either informative, reducing the set of response alternatives from four to two, or uninformative. Besides RT and LRP, we also measured electromyographic (EMG) activity and the P300 ERP component. RT, P300 latency, and the interval between the signal and LRP onset were all shorter with informative than uninformative precues, but the timing of EMG activity relative to RT remained the same. Most importantly, precuing affected the LRP-RT interval. Implications for bisecting RT with LRPs and the identity of processes affected by precuing are discussed.