Alpha-band activity reveals robust representations of spatial position during the storage of non-spatial features in working memory

摘要

Visual working memory (WM) enables active maintenance of visual information via sustained patterns of stimulus-specific activity (Harrison & Tong, 2009; Serences et al., 2009). Past work has shown that observers can control which features of an object are maintained in WM (Serences et al., 2009; Woodman & Vogel, 2008). However, behavioral studies suggest that stimulus position enjoys a privileged status in WM (e.g., Rajsic & Wilson, 2014), raising the possibility that unlike non-spatial features, stimulus position may be necessarily maintained alongside to-be-remembered features. To test whether stimulus position is maintained during non-spatial WM tasks, we examined spatially selective alpha-band (8-12 Hz) activity using an encoding model of spatial selectivity. Using this approach, past work has shown that the scalp distribution of alpha-band activity tracks locations stored in WM (Foster et al., 2016). In Experiment 1, observers remembered the color of a sample stimulus. While the position of the sample stimulus varied trial-to-trial, stimulus position was irrelevant to the task and unpredictive of probe position. Nevertheless, alpha activity tracked the original location of the stimulus throughout the delay period, demonstrating that stimulus position was represented in the pattern of alpha-band activity. Experiment 2 established that these spatial representations are under volitional control rather than being an automatic consequence of sensory activity a?? when observers were asked to store one of two simultaneous presented sample stimuli, spatially selective alpha activity was amplified for the target item compared to the non-target item. In Experiment 3, we observed spatially selective activity throughout the delay period of an orientation WM task, suggesting that spatial representations are not specific to the storage of colors in WM but are seen during the storage of non-spatial features in WM more generally. Our findings show that active representations of stimulus position are retained during the maintenance of non-spatial features in WM.