Conflict defined by global gestalt can modulate binocular rivalry suppression

Abstract

Binocular rivalry suppression is thought to necessarily require local interocular conflict: the presence of incompatible image elements, such as orthogonal contours, in retinally corresponding regions of two monocular displays. Whether suppression can also be driven by conflict at the level of spatially nonlocal surface or object representations is unclear. Here, we kept local contour conflict constant while varying global conflict, defined by the gestalt formed by the two monocular displays. Specifically, each eye was presented with a grid of image elements (crosses or plusses), placed such that the two eyes' individual grid elements did not directly overlap but the grids as a whole did. In a "shared motion" condition, all elements moved in unison, inviting a gestalt made up of all elements across both eyes; in a "different motions" condition, the elements' trajectories differed between eyes, inviting a gestalt of two overlapping surfaces, each associated with one eye. Perceptual disappearances of image elements occurred more readily in the different motions condition, an observation that could not be explained by any between-condition differences in local contour conflict. In a second experiment, we furthermore established that, whereas perceptual disappearances in the shared motion condition tended to involve a single element at a time, in the different motions condition, multiple elements belonging to the same gestalt often disappeared together. These findings indicate that, even though binocular rivalry may critically rely on inhibition due to locally incompatible image elements, this inhibition also depends on the global gestalt to which these elements contribute.

Figure 1.

Schematic depiction of our stimulus. This figure illustrates the joint stimulus formed by both monocular images combined; the actual monocular image viewed by a given eye contained only a subset of the elements shown here, depending on condition (see Figure 2).

Figure 2.

Overview of the experiment conditions. Conditions differed with regard to the factor's motion and ocularity. The former refers to whether crosses moved in unison with plusses or, alternatively, out of phase with them. The latter refers to the way in which crosses and plusses were distributed between the two eyes.

Figure 3.

Main result of Experiment 1. The conditions of Experiment 1 (x-axis) differed with regard to the proportion of trials (y-axis) in which the perceptual disappearance of at least one image element (cross or plus) was reported (see text for details).

Figure 4.

Experiment 1: The within-trial moment at which the first perceptual disappearance was reported in two critical conditions. In both conditions, perceptual disappearances tended to first occur after several seconds of viewing the stimulus. Disappearances were more common in the different motion condition than in the same motion condition, consistent with the data shown in Figure 3.

Figure 5.

Result of the first block of Experiment 2. This block forms a replication of Experiment 1 (Figure 3) but with a more complete set of stimulus conditions. As in Experiment 1, conditions were found to differ with regard to the proportion of trials in which the perceptual disappearance of at least one image element (cross or plus) was reported.

Figure 6.

Result of the second block of Experiment 2. Here, reporting a perceptual disappearance terminated the trial, prompting the observer to report what disappeared: a single element (darkest shade), multiple elements of a single kind (intermediate shade) or multiple elements including both kinds (lightest shade). The relative contributions of the three kinds of disappearances differ between conditions (see text for details). Note that each bar here summarizes data only from those observers who reported any disappearances at all in the associated condition, because otherwise the relative contributions of the three report options are not defined for that observer and condition. Across the bars the number of observers included ranges between 8 and 11 (out of 12 observers included in the experiment), with an average of 9.3. The proportions displayed here are relative to the numbers of trials where a perceptual disappearance occurred to begin with; not relative to the overall trial numbers.