Visual continuity across saccades is influenced by expectations.

Abstract

As we make saccades, the image on each retina is displaced, yet our visual perception is uninterrupted. This is commonly referred to as transsaccadic perceptual stability, but such a description is inadequate. Some visual objects are stable (e.g., rocks) and should be perceived as such across saccades, but other objects may move at any time (e.g., birds). Stability is probabilistic in natural scenes. Here we extend the common notion of transsaccadic visual stability to a more general, ecologically based hypothesis of transsaccadic visual continuity in which postsaccadic percepts of objects depend on expectations about their probability of movement. Subjects made a saccade to a target and reported whether it seemed displaced after the saccade. Targets had varying probabilities of movement (ranging from 0.1-0.9) that corresponded to their color (spectrum from blue to red). Performance was compared before and after subjects were told about the color-probability pairings ("uninformed" vs. "informed" conditions). Analyses focused on signal detection and psychometric threshold measures. We found that in the uninformed condition, performance was similar across color-probability pairings, but in the informed condition, response biases varied with probability of movement, and movement-detection sensitivities were higher for rarely moving targets. We conclude that subjects incorporate priors about object movement into their judgments of visual continuity across saccades.