EEG activity underlying successful study of associative and order information

Two of the most well studied and ecologically relevant memory paradigms are memory for pairs ("associations") and ordered sequences ("serial lists"). Behavioral theories comprise two classes: those that use common mechanisms and those that use distinct mechanisms for study and retrieval of associations versus serial lists. We tested the common-mechanisms hypothesis by recording electroencephalographic activity related to successful study ("subsequent memory effect" [SME]) of pairs and short lists (triples) of nouns. Multivariate analysis identified four distributed patterns of brain activity: (1) right parietal activity throughout most of the study period that differentiated study of pairs from triples within subjects as well as exhibiting an SME that was significant for pairs but not for triples; (2) a left parietal and fronto-polar activity pattern that was reliable around 500 msec and later in the study trial, exhibiting an SME for pairs and a weaker, nonsignificant SME for triples; (3) a left frontal/right parietal topography in the middle of the study interval which covaried with speed and accuracy across subjects; and (4) a pattern resembling the late positive component preceded by an early potential which together covaried with accuracy in triples but slow response times for both pairs and triples. These patterns point to the relevance of three classic SME components (early, late positive, and slow components) from single-item memory to memory for structured information, but suggest that they reflect subsets of more complex spatio-temporal patterns. Our findings support common underlying mechanisms for study and recall of pairs and lists. However, existing models must be modified to account for differences in both the presence of certain study-relevant processes and in the relevance of these processes to performance measures for pairs versus serial lists.