Attentional signatures of perception: multiple object tracking reveals the automaticity of contour interpolation

Abstract

Multiple object tracking (MOT) is an attentional task wherein observers attempt to track multiple targets among moving distractors. Contour interpolation is a perceptual process that fills-in nonvisible edges on the basis of how surrounding edges (inducers) are spatiotemporally related. In five experiments, we explored the automaticity of interpolation through its influences on tracking. We found that (1) when the edges of targets and distractors jointly formed dynamic illusory or occluded contours, tracking accuracy worsened; (2) when interpolation bound all four targets together, performance improved; (3) when interpolation strength was weakened (by altering the size or relative orientation of inducing edges), tracking effects disappeared; and (4) real and interpolated contours influenced tracking comparably, except that real contours could more effectively shift attention toward distractors. These results suggest that interpolation's characteristics-and, in particular, its automaticity-can be revealed through its attentional influences or "signatures" within tracking. Our results also imply that relatively detailed object representations are formed in parallel, and that such representations can affect tracking when they become relevant to scene segmentation.

Figure 1.

Stimuli and trial sequence in Experiment 1. (A) In all trials, a pair of black disks appeared within each quadrant of a white screen. Disks within a quadrant orbited about a central point (barycenter) at a random speed and direction (clockwise or not). Velocity varied between, not within, quadrants. (B) During a portion of the trial, white notches (sectors) appeared on all disks. The orientation and angle of sectors defined the four conditions. All conditions involved collinear edge relations between objects in adjacent quadrants (depicted by dotted lines). In the “target interpolate” (TI) condition, sectors were oriented so that the set of targets (illustrated here with “T”s) and set of distractors could each form an illusory quadrilateral. The “target contour relation” (TCR) condition was just like the TI condition, except that sectors were reflected so that they opened away from the central area. The “target distractor interpolate” (TDI) condition was the same as the TI condition, except that each target interpolated with distractors in its two neighboring quadrants. The target distractor contour relation (TDCR) condition was just like the TDI condition, except that sectors appeared with angles oriented opposite to where they would have been in the TDI condition. (C) In each trial, one disk in each quadrant blinked, denoting it as a target. When movement began, white sectors appeared over all disks (here, the TI condition is shown). Disks orbited for 5.5 s. At a random point within the following second, sectors disappeared. After a total of 7 sec of orbiting, all objects stopped, and participants attempted to identify the targets with a mouse. (Effects of each condition can best be apprehended by examining the movies in the supplementary materials or at www.briankeane.org.) Stimuli and trial sequences in the remaining experiments were variations of those depicted here.

Figure 2.

Mean accuracy and error bars (95% confidence intervals) for each condition in Experiment 1. Error bars for this graph and all other graphs do not include between-subject variance (Loftus & Masson, 1994).

Figure 3.

Stimuli in Experiment 2. Stimuli were the same as those in Experiment 1, except that each disk in all conditions was accompanied by a 1 arcmin ring around its circumference. To the left is a possible snapshot of either the TI or TDI condition; to the right, a possible snapshot of either the TCR or TDCR condition. Dotted lines reveal how the sectors of adjacent disks were related, and are for illustration only. The small central square was the fixation point.

Figure 4.

Mean accuracy and 95% confidence intervals for each condition of Experiment 2.

Figure 5.

Stimuli in Experiment 3. Versions of the TI and TDI conditions were each examined at four different average support ratios. Since the average distance between disks was always the same as Experiment 1, average support ratio values completely depended on disk size. The prediction was that as disks became smaller, interpolation strength would decrease, and so too would the accuracy difference between the TI and TDI conditions.

Figure 6.

Mean accuracy and 95% confidence intervals for each support ratio for both the TI and TDI conditions in Experiment 3. Support ratio is plotted from highest (stronger predicted interpolation effect) to lowest.

Figure 7.

Stimuli in Experiment 4. (A) Inducers were individually rotated with an angle α from where they would have been in the TI or TDI condition. The upper right and lower left quadrant inducers could only rotate clockwise; the other inducers could only rotate counter-clockwise. (B) Possible snapshots of either the TI or TDI condition are shown for each of the three rotation angles: 0 deg, 12 deg, and 48 deg. Dotted lines indicate how the edges of adjacent inducers were related, and are for illustration only.

Figure 8.

Results in Experiment 4. Accuracy and 95% confidence intervals are plotted for the TI and TDI conditions for each of the three inducer rotation angles. Doubling the inducer rotation angle gives the turn angle required for an interpolated contour to connect a pair of inducers.

Figure 9.

Possible snapshots of either the TR or TDR conditions in Experiment 5. The TR and TDR were just like the TI and TDI, respectively, except that thin black lines were drawn between the centers of the disks exactly when the disk sectors were present.

Figure 10.

Results in Experiment 5. Mean accuracy and 95% confidence intervals are plotted for when the grouping contours were interpolated or real, and for when targets grouped with one another or with distractors.