Multiple bottlenecks in information processing? An electrophysiological examination

When two stimuli are to be processed in rapid succession, reaction time (RT ) to the second stimulus is delayed. The slowing of RT has been attributed to a single processing bottleneck at response selection (RS) or to a centra l bottleneck following the initiation of the first response. The hypothesis of a response initiation bottleneck is mainly based on reports of underadd itive interactions between stimulus onset asynchrony (SOA) and the number o f stimulus-response alternatives (simple vs. two-choice response). The pres ent study tested the hypothesis of a response initiation bottleneck by reco rding the lateralized readiness potential (LRP), a brain wave, emerging dur ing or immediately following RS. The LRP findings were consistent with a ce ntral bottleneck but did not support the late bottleneck hypothesis. Instea d, the LRP provided direct evidence that the underadditive interaction of n umber of alternatives and SOA is due to an increase of response anticipatio ns in the simple response condition.