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Ryan W. Kasper, Joyce Sato-Reinhold, Scott T. Grafton, Miguel P. Eckstein, Barry Giesbrecht; fMRI responses during visual search predict the magnitude of EEG and behavioral benefits of repeated context. Journal of Vision 2011;11(11):1346. doi: 10.1167/11.11.1346.
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In visual search tasks, there are clear performance benefits when the spatial configuration of targets and distractors is repeated – a phenomenon known as the contextual cueing effect (Chun & Jiang, 1998). Initial accounts suggested that this benefit emerges out of an interaction between the neural mechanisms involved in attention and those involved in long-term memory (eg., hippocampus), but evidence for this hypothesis has been mixed (Chun & Phelps, 1999; Manns & Squire, 2001; Greene et al., 2007; Preston & Gabrieli, 2008). Here we investigated the neural bases of the contextual cueing effect by probing the relationship between hippocampus responses recorded using fMRI and both the size of the attention-related N2pc event-related potential and the behavioral contextual cueing effect. Eleven subjects performed a visual search task in two sessions, each consisting of 256 trials (50% repeated configurations). In session 1, 64-channel EEG and whole-brain fMRI data were acquired simultaneously. Session 2 occurred one week later and was identical to session 1, except that only 64-channel EEG data was recorded. A hippocampal region-of-interest (ROI) was defined a priori and the BOLD percent signal change was computed for repeated and novel displays. A rank-ordering analysis was used to assess the relationship between the hippocampus, the N2pc, and behavior. This analysis revealed that the magnitude of the difference between repeated and novel displays in the hippocampus ROI could rank order individuals based on the size of the cueing effects observed in session 1 (60%) and session 2 (56%) significantly better than chance (p < 0.01). Hippocampal activity also accurately rank ordered the size of the N2pc from session 1 (56%) and from session 2 (64%, both above chance, p < 0.01). These results illustrate that the response of the hippocampus early in learning can predict the level of eventual behavioral benefit of repeated spatial configurations.
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