Divisive Normalization and the Flexible Resolution of Ambiguity

Our visual systems usually construct a useful and unambiguous representation of the world. When the visual system is presented with multiple compelling interpretations of the same space, neural populations compete for perceptual dominance to resolve ambiguity. Spatial and temporal context can guide the build-up of perceptual experience. Recent evidence shows that ambiguous representations can be resolved by enhancing differences between ob- jects in view, in addition to enhancing perceived similarity (so-called interocular grouping, Peiso and Shevell, 2020). This dissertation investigated the possible role of divisive normalization in the resolution of ambiguous neural representations. The reported experiments use rivalrous dichoptic stimuli presented in interocular-switch rivalry to evoke neural ambiguity and observer reports of perceptual experience. Four experiments manipulated either the feature relations within a rivalrous dichoptic signal (Experiment 1) or adjacent non-rivalrous regions (Experiments 2-4) to investigate the influence of spatiochromatic context on the resolution of ambiguity. Within a single trial, observers' reports revealed the duration that various stimuli resulted in similarity-enhanced or difference-enhanced percepts. Similarity- enhancement refers to the resolution of percepts that reduce the visual distinctiveness of (1) rivalrous regions from each other or (2) rivalrous regions from their shared background; conversely, difference-enhancement refers to the resolution of percepts that increase the visual distinctiveness of objects in view. The motivating theoretical framework integrated divisive normalization accounts of attention and figure-ground processing to explain the perceptual flexibility observed in binocular rivalry experiments. Four experiments supported the hypothesis that a context-dependent divisive-normalization mechanism acts on a rivalrous chromatic signal to alter the resolution of ambiguity.