Is the effect of distractors in multiple object tracking dependent on the distractors sharing the features of the targets? In experiment 1, observers tracked five targets among five distractors that were identical to the targets and a number of additional distractors that were either identical to or featurally distinct from the targets. Results showed that distractors that are distinct from the targets in shape or color, or are stationary, impair tracking less than distractors that are identical to the targets. However, tracking performance declined as the number of distractors increased, even for featurally distinct distractors. Experiment 2 showed that distractors that differ from the targets on two features impair tracking less than distractors that differ from the targets on only one feature, but only when target tracking load is low. These results indicate that shape, color, and motion information about distractors can be used to distinguish them from targets during tracking, although even distractors with a different feature from the targets produce some interference with tracking. These findings suggest that the effect of distractors on tracking is dependent on top-down settings for target features.

Sinai et al (1998 Nature 395 497-500) showed that less distance is perceived along a ground surface that spans two differently textured regions than along a surface that is uniformly textured. We examined the effect of texture continuity on judged distance using computer-generated displays of simulated surfaces in five experiments. Discontinuities were produced by using different textures, the same texture reversed in contrast, or the same texture shifted horizontally. The simulated surface was either a ground plane or a frontoparallel plane. For all textures and both orientations, less distance was judged in the discontinuous conditions than in continuous conditions. We propose that when a surface contains a texture discontinuity, a small area adjacent to the perceived boundary is excluded from judged distances.

Multiple-object tracking (MOT) studies have shown that tracking ability declines as object speed increases. However, this might be attributed solely to the increased number of times that target and distractor objects usually pass close to each other ("close encounters") when speed is increased, resulting in more target-distractor confusions. The present study investigates whether speed itself affects MOT ability by using displays in which the number of close encounters is held constant across speeds. Observers viewed several pairs of disks, and each pair rotated about the pair's midpoint and, also, about the center of the display at varying speeds. Results showed that even with the number of close encounters held constant across speeds, increased speed impairs tracking performance, and the effect of speed is greater when the number of targets to be tracked is large. Moreover, neither the effect of number of distractors nor the effect of target-distractor distance was dependent on speed, when speed was isolated from the typical concomitant increase in close encounters. These results imply that increased speed does not impair tracking solely by increasing close encounters. Rather, they support the view that speed affects MOT capacity by requiring more attentional resources to track at higher speeds.

No abstract

Previous research has indicated that observers use differences between velocities and ratios of velocities to judge the depth within a moving object, although depth cannot in general be determined from these quantities. In four experiments we examined the relative effects of velocity difference and velocity ratio on judged depth within a transparent object that was rotating about a vertical axis and translating horizontally, examined the effects of the velocity difference for pure rotations and pure translations, and examined the effect of the velocity difference for objects that varied in simulated internal depth. Both the velocity difference and the velocity ratio affected judged depth, with difference having the larger effect. The effect of velocity difference was greater for pure rotations than for pure translations. Simulated depth did not affect judged depth unless there was a corresponding change in the projected width of the object. Observers appear to use the velocity difference, the velocity ratio, and the projected width of the object heuristically to judge internal object depth, rather than using image information from which relative depth could potentially be recovered.