Abstract
Previous research reveals that several independently moving objects can be tracked with attention, suggesting that attention may be split into multiple, independent foci. This study aims to test whether the attentional foci are fully independent of each other, or whether they are yoked together during tracking. We asked viewers to track 4 designated moving circles among a field of 8 circles and measured tracking accuracy as a function of the objects' motion characteristics. In Experiment 1, all eight objects moved at the same speed on a given display (the speed could be slow, medium, fast, or very fast on different trials), or the four targets moved at four different speeds among nontargets that also moved at these four speeds. In both conditions speed did not distinguish the tracking targets from nontargets. However, tracking was better when all objects moved at the same speed than when they moved at different speeds. This finding suggests that multiple attentional foci are interdependent and function best at a uniform speed. Experiments 2 and 3 introduced redundancy in motion trajectories, such that a varying number of objects moved briefly in parallel to each other on 50% of time during a motion trial. Tracking accuracy was higher when the number of correlated targets or correlated nontargets increased but did not change when the motion trajectories of targets were correlated with those of nontargets. This finding suggests that the correlation was used to establish segregation between targets and nontargets. We conclude that multiple attentional foci are not completely independent but are yoked to facilitate perceptual segregation of attended from unattended objects.
This study was supported in part by NSF 0733764 and NIH 071788.