Multistable perception—where sensory ambiguity causes spontaneous alternations between two or more perceptual interpretations—occurs across many animal species. This review covers research on visual perceptual rivalry in insects, fish, reptiles, and primates, highlighting binocular rivalry and the Necker cube as examples. Common behavioral indicators of perceptual alternation appear across species. The comparative approach offers insights into how brains suppress conflicting sensory signals and generate shifts in perceptual dominance, suggesting that ambiguous sensation is a fundamental problem that has shaped brain evolution.
A structural approach to studying consciousness maps mathematical descriptions of qualia—the qualitative aspects of conscious experience—onto mathematical structures derived from brain activity and neuronal connectivity, aiming for general mappings akin to physical laws like E=mc². This review surveys literature from psychophysics and the neuroscience of consciousness, critically examines classical models such as Shepard's pitch helix and visual color space, and explores the structure of their neuronal correlates. It extends analysis to visual similarity spaces, including face space and general image spaces, and suggests that exact experimental comparisons yield an enriched psychophysics that expands single-valued measures into richer scientific exploration.