Which perceptual categories do observers experience during multistable perception?

Multistable perceptual phenomena provide insights into the mind's dynamic states within a stable external environment, and the neural underpinnings of these consciousness changes are often studied with binocular rivalry (BR). Conventional methods to study binocular rivalry suffer from biases and assumptions that limit their ability to describe the continuous nature of these perceptual transitions and to discover what kind of percept was perceived across time. Recently, we developed a new method to avoid those shortcomings, called InFoRM-Rivalry. The method builds customized regions of six principal perceptual categories that are described in the literature, including two exclusive and four mixed perceptual categories, i.e. piecemeal (one) and superimposition (three). We re-analysed data using unsupervised clustering to determine where within these principal categories clusters of perception naturally occur. We show that, on average, 10 ± 8 categories arise and that these categories map predominately onto the exclusive and superimposed principal regions regardless of the stimulus contrast configurations. Next, we estimated the most likely transition pathways during binocular rivalry using a Hidden Markov model and showed that transitions are most likely to appear between monocular exclusive and binocular superimposed categories. These results suggest that binocular rivalry, triggered by low-level grating stimuli, involves conflict between monocular and binocular neural processing sites rather than only mutual inhibition of monocular sites.