Chunking processes in the learning of event sequences: Electrophysiological indicators

The present study investigated whether effects of implicit learning (IL) ar e due to well-learned and explicitly represented parts of the stimulus mate rial ("chunks"). To this purpose, event-related brain potentials (ERPs) wer e recorded during an oddball-version of a serial reaction time (RT) task: A t unpredictable positions within a 16-item letter sequence, single deviant items replaced an item of the repeatedly presented standard sequence. After acquisition, the "process dissociation procedure" (Jacoby, 1991) was adopt ed to identify explicitly learned sequence parts for each participant. Acqu isition of sequence knowledge was reflected in faster RTs for standard item s than for deviant items and in enhanced N2b and P3b components for deviant items. While the ERP effects were obtained for explicitly represented sequ ence parts only, RT effects were independent of subsequent reproduction per formance. These results indicated that (1) ERPs are a valid measure of expl icit knowledge, (2) implicit and explicit knowledge coexist in serial RT ta sks, and (3) chunking processes play a major role in the acquisition of exp licit knowledge about event sequences.