Brain mechanisms for simple perception and bistable perception

Significance When viewing an image with multiple interpretations such as the Necker cube, subjective perception alternates stochastically between the different interpretations. This phenomenon provides a well-controlled experimental approach to studying how the brain responds to ambiguities in sensory inputs—a ubiquitous problem in dealing with natural environment. We found that, compared with simple perception devoid of ambiguities, bistable perception requires additional higher-order brain regions and dramatically enhanced top-down and bottom-up influences in the brain. Intermittent viewing of ambiguous images elicits even stronger top-down brain activity. These results help elucidate the mechanisms of visual perception by demonstrating an active top-down inferential process. When faced with ambiguous sensory inputs, subjective perception alternates between the different interpretations in a stochastic manner. Such multistable perception phenomena have intrigued scientists and laymen alike for over a century. Despite rigorous investigations, the underlying mechanisms of multistable perception remain elusive. Recent studies using multivariate pattern analysis revealed that activity patterns in posterior visual areas correlate with fluctuating percepts. However, increasing evidence suggests that vision—and perception at large—is an active inferential process involving hierarchical brain systems. We applied searchlight multivariate pattern analysis to functional magnetic resonance imaging signals across the human brain to decode perceptual content during bistable perception and simple unambiguous perception. Although perceptually reflective activity patterns during simple perception localized predominantly to posterior visual regions, bistable perception involved additionally many higher-order frontoparietal and temporal regions. Moreover, compared with simple perception, both top-down and bottom-up influences were dramatically enhanced during bistable perception. We further studied the intermittent presentation of ambiguous images—a condition that is known to elicit perceptual memory. Compared with continuous presentation, intermittent presentation recruited even more higher-order regions and was accompanied by further strengthened top-down influences but relatively weakened bottom-up influences. Taken together, these results strongly support an active top-down inferential process in perception.