Implicit and explicit learning of event sequences: evidence for distinct coding of perceptual and motor representations

Event-related brain potentials (ERPs) of 21 subjects were recorded in a cho ice reaction time task with a repeating eight-element long stimulus sequenc e. The regular event sequence was sometimes interrupted by 'perceptual' or by 'motor deviants' which both replaced an expected stimulus but either pre served or violated the sequence of motor responses. Response times confirme d that all subjects had acquired some knowledge of the sequential dependenc ies. By means of a post-experimental free recall and recognition test, subj ects were classified as having either explicit or implicit knowledge of the event sequence. The ERPs showed different effects for different types of s timuli and the two groups. In the group of explicit learners, a larger N200 component was evoked by both types of deviants and a larger P300 by motor deviants only. In the group of implicit learners these 'perceptual componen ts' remained unaffected. In contrast, in both groups of subjects the latera lized readiness potential (LRP) which accompanied motor deviants revealed a partial activation of the to be expected but incorrect response, i.e. moto r learning. These results suggest that explicit learners acquire knowledge about both, stimulus and response dependencies while implicit learners acqu ire knowledge about response dependencies only. (C) 2000 Elsevier Science B .V. All rights reserved.