Grouping in visual working memory is determined by the task context
33.4109, Sunday, 17-May, 8:30 am - 12:30 pm, Pavilion
Halely Balaban1,2, Roy Luria1,2; 1Sagol School of Neuroscience, Tel Aviv University, Israel, 2The School of Psychological Sciences, Tel Aviv University, Israel
Visual working memory (WM) can only hold a very limited amount of information, and one way to overcome this capacity limitation is to group several items to one chunk. While perceptual grouping may be regarded as preattentive, grouping in WM should be flexible enough to allow WM representation to adapt to a changing environment. We examined the influence of context on grouping of color-color conjunctions in WM. We used a change detection paradigm with moving colored squares as stimuli, and monitored the contralateral delay activity (CDA), an electrophysiological marker whose amplitude rises as more items are stored in WM. We compared a "common fate" condition (two color-color conjunctions that moved together) to two and four separate colors. If the common fate conjunctions are grouped, the CDA amplitude should be similar to two separate colors. Conversely, if the conjunctions are represented separately, the CDA amplitude should be similar to four separate colors. Critically, while these exact three conditions appeared in all experiments, we manipulated the presence of an additional condition that served as a context cue. When the additional condition included four separately-moving colors that met and then moved together, the CDA amplitude of the common fate conjunctions was identical to two separate colors, indicating perfect grouping. Without the "joining" condition, the common fate conjunctions were initially grouped but then individuated during their memory maintenance, producing a CDA amplitude higher than two colors. When the joining condition was replaced by a separating condition (two color-color conjunctions that separated to four colors), the CDA amplitude of the common fate condition gradually rose until it reached that of four separate colors, indicating increasing individuation. Our results suggest that grouping in WM is highly sensitive to environmental cues, with items being grouped when the context implies "togetherness" and individuated when it implies independence.