Impact of Semantic Relatedness on Associative Memory: An ERP Study

Encoding and retrieval processes in memory for pairs of pictures are thought to be influenced by inter-item similarity and by features of individual items. Using Event-Related Potentials (ERP), we aimed to identify how these processes impact on both the early mid-frontal FN400 and the Late Positive Component (LPC) potentials during associative retrieval of pictures. Twenty young adults undertook a sham task, using an incidental encoding of semantically related and unrelated pairs of drawings. At test, we conducted a recognition task in which participants were asked to identify target identical pairs of pictures, which could be semantically related or unrelated, among new and rearranged pairs. We observed semantic (related and unrelated pairs) and condition effects (old, rearranged and new pairs) on the early mid-frontal potential. First, a lower amplitude was shown for identical and rearranged semantically related pairs, which might reflect a retrieval process driven by semantic cues. Second, among semantically unrelated pairs, we found a larger negativity for identical pairs, compared to rearranged and new ones, suggesting additional retrieval processing that focuses on associative information. We also observed an LPC old/new effect with a mid-parietal and a right occipito-parietal topography for semantically related and unrelated old pairs, demonstrating a recollection phenomenon irrespective of the degree of association. These findings suggest that associative recognition using visual stimuli begins at early stages of retrieval, and differs according to the degree of semantic relatedness among items. However, either strategy may ultimately lead to recollection processes

Event-related potentials during learning and recognition of complex pictures

grantor: University of TorontoEvent-related potentials (ERPs) were recorded while subjects learned a large set of complex, coloured pictures. Recognition memory was examined within the same day and after a 24 hour lag. Memory performance decreased from 88% to 65% over 24 hours. The ERP waveforms showed a prominent parietal-occipital P100-N150-P240 complex that was the same in learning and recognition. A centro-parietal P650 wave was larger during recognition than during learning for both the new and old pictures. During learning the pictures elicited a sustained positive potential maximally recorded in the occipital regions. Finally, in the recognition condition, new pictures elicited an N400 wave over frontal electrodes while old pictures elicited an earlier centroparietal P650 than novel pictures. Learning is most clearly associated with a sustained occipital positivity, recognition with a parietal positive wave, and novelty-detection with a frontal negative wave.M.A