Are visual working memory and multiple object tracking limited by a common attention capacity?

Abstract

About 4 objects can be kept in visual working memory (VWM) and about 4 objects can be visually tracked simultaneously in the Multiple Object Tracking (MOT) task. This resemblance was caught by Cowan (2001) as evidence for a common attention limit underlying both VWM and MOT. Consistent with Cowan's argument, fMRI studies showed that the activation of the posterior parietal cortex increases with the number of items in VWM or MOT. However, it should be noted that MOT is closely associated with location information whereas many VWM tasks demand a comparison of visual properties at the same location in sample and probe displays. So it might be the processing of spatial information that leads to the similarity between VWM and MOT. We tested this possibility in two experiments by examining the dual-task interference of MOT and VWM. In Experiment 1, we found that there was interference between VWM for color-location combination and MOT but no interference between VWM for color-shape combination and MOT. In Experiment 2, we further tested whether tracking more targets would lead to more impairment on location-relevant VWM and found that it depended on speed of objects in MOT. Only under low speed did more targets lead to more impairment. In summary, our results suggest that VWM and MOT might share some capacity-limited resource related to spatial processing, but not a common attention resource.