Abstract
Question: Subjects can simultaneously track four target objects that move among an equal number of moving distractors. It is unknown whether inter-object contour relations—especially those that promote interpolation— can affect multiple object tracking. Method: Ten subjects each performed 160 trials in which four out of eight moving objects were tracked. Objects appeared initially as circles, changed into wedged circles with movement onset, and returned to full circles 1 sec before movement cessation. There were four conditions. In two conditions, wedged circles always produced two interpolated (Kanizsa) quadrilaterals that changed shape with object movement. To ensure that quadrilaterals never collapsed, two objects were confined to each quadrant - one was always a target and one always a distractor. In the first interpolation condition, four targets formed the vertices of one of the interpolated quadrilaterals (TI condition). In the second condition, two targets aligned with two distractors to form each of two interpolated quadrilaterals (TDI condition). In two otherwise identical control conditions, the wedged circles were oriented outward to block perception of an interpolated figure. In these trials, all four targets maintained a constant contour relation toward one another (TC condition), or a set of two targets and two distractors maintained such a relation (TDC condition). Results: The difference between the TI and TDI conditions was greater than the difference between the TC and TDC conditions. Tracking was reliably worse in the TDI than in either the TI or TDC conditions. Conclusions: These data suggest that contour interpolation, though perhaps not other sorts of contour relations, can influence the ability to track multiple objects at a time. The data further suggest that contour relations of even unattended objects can affect multiple object tracking.
Supported by National Eye Institute EY13518 to PJK.