Adaptation to vergent and averted eye gaze.

Previous adaptation studies have revealed the tuning properties of mechanisms coding left-right averted gaze. Here, Experiment 1 used an adaptation procedure to investigate the mechanisms that encode vergent eye gaze. Following prolonged exposure to convergent or divergent gaze, observers were more likely to categorize smaller gaze deviations in the adapted direction as parallel (i.e., nonvergent). We then examined whether adaptation was occurring to the eyes independently (monocular gaze direction) as opposed to the two eyes as a unitary stimulus (binocular gaze direction). In Experiment 2, we interleaved presentations of convergent and divergent adaptors and tested with either congruent (vergent) or incongruent (left-right) stimuli. Similarly, we interleaved presentations of leftward- and rightward-averted adaptors and tested with congruent (left-right) and incongruent (vergent) stimuli. If adaptation were driven solely by monocular gaze direction, congruent and incongruent adaptation would be similar because, at the level of an individual eye, the stimuli are identical. We find considerable adaptation in the incongruent conditions, consistent with adaptation to individual eye directions. However, we also find greater adaptation in congruent conditions, implicating the involvement of mechanisms that encode binocular gaze direction.