Abstract
Several studies have shown that multiple object tracking (MOT) performance declines as the speed of the objects increases. One possible explanation for this is that increases in speed increase the number of times that targets and distractors pass close to each other (“close encounters”), resulting in more target-distractor confusions (e.g., Franconeri et al., 2010). Other possible explanations are that more attention is required to track fast-moving objects (e.g., Alvarez & Franconeri, 2007) or that it is more difficult to predict the future locations of fast-moving objects (Tombu & Seiffert, 2008). The present study investigates whether MOT performance is impaired by increases in speed that do not increase the number of close encounters. On each trial, there were six pairs of disks, and each pair rotated about the pair's midpoint, and about the center of the display. Observers tracked six target disks, one from each pair. The speed of rotation about the center of the display was the same for all disks on a given trial, and had four levels that were varied across trials. In these displays, increasing the speed of rotation about the center of the display increases the disks' speeds, but does not increase the number of close encounters. Tracking performance was found to decline as the speed of the disks increased. This demonstrates that even when the number of close encounters is held constant, speed still has an effect. While many studies have found that close encounters affect MOT, the results of the present study suggest that the increased number of close encounters is not the only cause of the impairment of MOT at higher speeds. Other factors, such as the increased attentional allocation required and the increased difficulty of predicting future locations, probably play roles in the reduction of tracking at higher speeds as well.
Supported by a California State University Research Funds grant and a grant from the San Jose State University College of Social Sciences.