THE TEMPORAL SELECTIVITY OF ADDITIVE FACTOR EFFECTS ON THE REACTION PROCESS REVEALED IN ERP COMPONENT LATENCIES

An experiment was conducted to relate individual components of the eve nt-related brain potential to specific stages of information processin g in a two-choice reaction time (RT) task in a group of undergraduate students. Specifically, the latency of the P300 component and the late ralized readiness potential (LRP) were studied as a function of variat ions in stimulus degradation and response complexity. It was hypothesi zed that degrading the stimulus would delay the P300 and LRP to the sa me extent as RT, and that increasing response complexity would affect RT but not P300 latency. The extant literature did not permit any hypo thesis regarding the effect of response complexity on LRP latency. The two task variables were found to have additive effects on RT. As pred icted, variations in stimulus degradation influenced the latencies of both components, whereas alterations in response complexity had no eff ect on P300 latency. A significant new finding was that the onset late ncy of the LRP remained unchanged across levels of response complexity . The overall pattern of results supports the notion of temporal selec tivity of stage manipulations that is derived from discrete stage mode ls of human information processing. Furthermore, these results refine the functional interpretation of the LRP by indicating that within the conceptual framework of a stage model the processes this component in dexes succeed the start of response choice but precede the start of mo tor programming.