Capturing regularities in event sequences: Evidence for two mechanisms

The processing of regular event sequences was investigated by presenting categorical visual events in sequences that followed a rule system and a category restriction. Participants' task was to detect deviations of the rule or category restriction (single deviants) or both (double deviants). In Experiment 1, participants detected double deviants faster and more accurately than single deviants. This result is compatible with statistical facilitation, i.e. with distinct information processing in two channels. Experiment 2 used the same paradigm but did not require an immediate behavioural response to deviants. Here, event-related brain potentials revealed a redundant deviance effect in the P3 component (i.e. shorter latency and larger amplitude for double deviants compared with either single deviant). Category restriction deviants additionally led to an increased P2 amplitude. It is suggested that rule and category restriction information is processed separately at central levels, and that two central stages can be distinguished in the processing of categorical visual sequence events that make different use of short-term and long-term memory resources.