Spatial Attention's Role in Active Memory Maintenance Depends on Whether Space is the Attended Feature

Space and time are thought to play a critical role in working memory (WM) formation and maintenance relative to other object features. Both features have been found to enable feature binding and to be incidentally encoded in memory. However, the extent that space and time operate as complementary codes or trade priority depending on task relevance remains an open question. Here we investigated if the relevance of spatial information affects whether spatial attention contributes to memory maintenance when items are separated in space and time. We report two experiments with human participants (male and female) that differed in whether location or color was the tested feature. In both experiments, we measured EEG alpha-band power while observers memorized the target feature of two sequentially presented colored dots. We then applied an inverted encoding model (IEM) to the topography of oscillatory alpha-band power (8 – 12 Hz) on the scalp to measure how long the location of each item was attended. In Experiment 1, observers performed a delayed spatial estimation task, and we found that patterns of alpha-band power tracked each item’s location throughout the duration of the trial. In Experiment 2, observers performed a delayed color estimation task, and we found that patterns of alpha-band power only tracked the location of the most recently presented item. Together, our results show that multiple locations are actively attended over a sequence when they are the tested feature, but that spatial attention tracks maintenance of only the most recent item when location is irrelevant.