Coding of navigational affordances in the human visual system

Significance As we move about the world, we use vision to determine where we can go in our local environment and where our path is blocked. Despite the ubiquity of this problem, little is known about how it is solved by the brain. Here we show that a specific region in the human visual system, known as the occipital place area, automatically encodes the structure of navigable space in visual scenes, thus providing evidence for a bottom-up visual mechanism for perceiving potential paths for movement in one’s immediate surroundings. These findings are consistent with classic theoretical work predicting that sensory systems are optimized for processing environmental features that afford ecologically relevant behaviors, including the fundamental behavior of navigation. A central component of spatial navigation is determining where one can and cannot go in the immediate environment. We used fMRI to test the hypothesis that the human visual system solves this problem by automatically identifying the navigational affordances of the local scene. Multivoxel pattern analyses showed that a scene-selective region of dorsal occipitoparietal cortex, known as the occipital place area, represents pathways for movement in scenes in a manner that is tolerant to variability in other visual features. These effects were found in two experiments: One using tightly controlled artificial environments as stimuli, the other using a diverse set of complex, natural scenes. A reconstruction analysis demonstrated that the population codes of the occipital place area could be used to predict the affordances of novel scenes. Taken together, these results reveal a previously unknown mechanism for perceiving the affordance structure of navigable space.