INFLUENCE OF REMOTE OBJECTS ON LOCAL DEPTH-PERCEPTION

The perceived relative depth of two test dots displayed within the fovea is shown to be influenced by other features in the surrounding area. These features can be as far apart as 51 deg and can have relative disparities as large as 20 deg, much larger than the disparities of the test dots. Since this effect is seen for stimuli presented for 100 msec or less, changes in direction of gaze cannot play a role. The effect varies inversely as the spatial separation between the test dots and the remote features, and is insensitive to the relative disparities of these remote features when they are greater than 2 deg. Observers sometimes differ significantly from each other in their responses to various configurations of the outlying features. This appears to rule out response mechanisms which depend only on the stimulus; some characteristics of the observer must be involved in determining the response. For these briefly presented stimuli, observers are unable to report accurately the relative depth of the central foveated test items if they are also required to report the depths of distant peripheral features.