The effects of working memory load on visual awareness and its electrophysiological correlates.

Abstract

Consciousness and working memory (WM) have been thought to be closely related, but their exact relationship has remained unclear. The present study focused on the question whether visual awareness, the subjective experience of seeing, depends on resources of WM. Three dual-task experiments were run. The participants were asked to report their awareness of a low-contrast target stimulus while their WM was loaded by a requirement to concurrently maintain verbal information (Experiment 1) or visuo-spatial information (Experiment 2) in WM, or by a concurrent executive task (Experiment 3). Behavioral responses and event-related brain potential (ERP) correlates of visual awareness in response to the targets were examined. Experiments 1 and 2 revealed that maintenance of information in WM did not have any effect on reported visual awareness and its electrophysiological correlates. Experiment 3 found that executive load decreased reported visual awareness, which was reflected in ERPs around 350-550 ms after stimulus onset as a reduction in the amplitudes of P3 to detected stimuli. The earlier, posterior correlate of visual awareness in N200 time window (180-280 ms) was not affected by load in any of the conditions. The results suggest that visual consciousness and WM share resources at a relatively late stage of conscious processing, which involves active manipulation of contents. The findings are in line with a recent view suggesting that a posterior "hot zone" is responsible for visual awareness, while frontal regions contribute to higher-level cognitive processes that occur after visual awareness has arisen.