Are odd things all the same? Physical and semantic distinctiveness, memory, and event-related brain potentials

Distinctive (isolated) events are usually recalled better than common events (isolation effect). Previous research showed that components of the event-related brain potential (ERP) can be used as indices of the encoding processes elicited by distinctive events. In particular, the larger the P300 component of the ERP elicited by isolated words, the more likely it was for these words to be recalled. This suggests that the isolates evoke encoding processes whose intensity is indexed by the amplitude of P300.This study examined: (a) the role of encoding processes in determining the isolation effect; (b) the extent to which biases in the subject's attention influence these encoding processes; (c) the importance of similarity between encoding and retrieval context in determining the isolation effect; (d) the extent to which different types of distinctive events are similarly encoded.Subjects were assigned either a physical (size judgment) or a semantic (lexical decision) orienting task. They were presented with series of stimuli containing both physical and semantic isolates (words differing from the other stimuli in the series in either character size or semantic category). The ERPs elicited by each stimulus were recorded. Subjects performed a free recall test at the end of each series. They also performed two types of recognition tests, only one of which reinstated the encoding context.Subjects performing the physical task showed a physical but not a semantic isolation effect in free recall and the physical isolates elicited P300s larger than those elicited by nonisolated words. Subjects performing the semantic task displayed both semantic and physical isolation effects, and both types of isolates elicited large P300s. However, for both groups of subjects, the amplitude of P300 at encoding predicted the recall of both types of isolates. In the recognition tests the isolation effect was obtained only when the encoding context was reinstated. The amplitude of P300 at encoding predicted recognition performance.These results suggest that: (a) encoding processes, as indexed by the P300, are important in determining the isolation effect; (b) biases induced by the orienting task influence the extent to which distinctive features are processed; (c) it is necessary to reinstate the encoding context; (d) physically and semantically distinctive words appear to elicit similar encoding processes.U of I OnlyETDs are only available to UIUC Users without author permissio