The interaction of perceptual biases in bistable perception

Abstract

When viewing ambiguous stimuli, people tend to perceive some interpretations more frequently than others. Such perceptual biases impose various types of constraints on visual perception, and accordingly, have been assumed to serve distinct adaptive functions. Here we demonstrated the interaction of two functionally distinct biases in bistable biological motion perception, one regulating perception based on the statistics of the environment - the viewing-from-above (VFA) bias, and the other with the potential to reduce costly errors resulting from perceptual inference - the facing-the-viewer (FTV) bias. When compatible, the two biases reinforced each other to enhance the bias strength and induced less perceptual reversals relative to when they were in conflict. Whereas in the conflicting condition, the biases competed with each other, with the dominant percept varying with visual cues that modulate the two biases separately in opposite directions. Crucially, the way the two biases interact does not depend on the dominant bias at the individual level, and cannot be accounted for by a single bias alone. These findings provide compelling evidence that humans robustly integrate biases with different adaptive functions in visual perception. It may be evolutionarily advantageous to dynamically reweight diverse biases in the sensory context to resolve perceptual ambiguity.

Figure 1. Illustrations of bistable point-light walker (PLW) stimuli and the possible percepts in the consistent and the conflicting experimental conditions.

The lines connecting the dots (displayed for illustration only) illustrate the depth information: white lines represent the body parts closer to the viewer, and black lines represent parts that are farther in depth. (A) Viewpoints of the two possible percepts for the consistent condition, indicated by blue cameras; and for the conflicting condition, indicated by orange cameras. θ represents the angle of deviation from the horizontal plane, which ranges from 45° to 5° and can be considered as either the angle of elevation or the angle of depression for each stimulus, depending on which percept is referred to. (B) Orthogonally projected PLW stimuli (central) and their corresponding percepts (left and right).

Figure 2. Results of Experiment 1.

(A) Perceptual reversals as a function of time in the consistent and the conflicting conditions. The panels from top to bottom display sample trials from three observers with slow, medium and fast switch rates, respectively. (B) Mean switch rates for the consistent and the conflicting conditions. Error bars denote ± SEM.

Figure 3. Results of Experiment 2a (angular deviations: 35°, 20°; large angles) and Experiment 2b (angular deviations: 15°, 10°, 5°; small angles).

(A) Mean proportions of Above_Toward responses in the consistent condition and Above_Away responses in the conflicting condition for Experiment 2a (Large angles) and 2b (Small angles). (B) Mean proportions of the dominant responses in the consistent and the conflicting conditions respectively at each angular deviation. Error bars denote ± SEM.

Figure 4. Results of Experiment 3 (angular deviations: 25°, 20°, 15°, 10°, 5°).

(A) Mean proportions of Above_Toward responses in the consistent condition and Above_Away responses in the conflicting condition as a function of angular deviation. (B) Mean proportions of the dominant responses along 5 angles of deviation in the consistent and the conflicting conditions. (C) Proportions of Above_Away responses in the conflicting conditions (upper-left panel) and proportions of Above_Toward responses in the consistent conditions (upper-right panel) for individual observers, as well as the correlation between them at each camera angle (lower panels). Error bars denote ± SEM.