Event-Related Potential (ERP) Studies of Spatial Working Memory

Abstract

This dissertation aims to characterize the neural processes in association with the updating and storage of spatial information. Selective information processing has been suggested as the underlying mechanism for updating and selective maintenance of object information in working memory. It is unclear whether similar mechanism is involved in updating spatial information. Furthermore, it is unclear whether the neural representation of no longer relevant spatial information would show transient or sustained effects on working memory. Two event-related potentials (ERPs) experiments were conducted to examine (1) the neural processes involved in selecting relevant spatial locations from working memory and the subsequent effect on recognition, and (2) the timing at which relevant and no longer relevant spatial locations were separately represented and whether the post-updating neural activity was modulated by different amounts of relevant and no longer relevant information. Behavioral and neural data were collected from 54 participants in two experiments. Participants performed a variant of the delayed recognition paradigm, in which a memory selection cue was inserted during the retention interval to indicate memory updating. Results from Experiment 1 showed that the instruction cue modulated the neural activity of four prominent ERP components between 140-700 ms after cue onset. These components reflect processing of cue meaning, refocusing of relevant information, memory retrieval of relevant information, and content reorganization. Successful working memory updating was also found to modulate the behavioral and neural responses to recognition. Results from Experiment 2 showed separation of neural representation of relevant and no longer relevant information within the first 300 ms of the post-updating interval. Neural representation of relevant information showed strong and widespread sustained effects over the left frontal to parietal regions. Neural representation of no longer relevant information, in contrast, showed a weak sustained effect and was restricted to the left frontal region. The findings suggested that updating of spatial working memory involved several prominent neural processes, which began early in the cue period. Also, both relevant and no longer relevant information showed sustained effects on maintenance throughout the delay period.