PURPOSE: 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. For instance, in bistable biological motion perception, the viewing-from-above (VFA) bias regulates perception based on the statistics of the environment and the facing-the-viewer (FTV) bias has the potential to reduce costly errors resulting from perceptual inference. Yet it remains unclear whether our brain combines such discrepant biases to make sense of the sensory world.
METHODS: We adopted orthographically projected point-light-walker (PLW) stimuli and manipulated the angular deviation from the horizontal plane to modulate degrees of the FTV bias and the VFA bias within a single scenario.
RESULTS: 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. Nevertheless, 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.
CONCLUSIONS: 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.