Temporal integration of stereo and motion information

Studies of depth cue integration usually focus on the combination of different sources of 3D information present in the same spatial and temporal location. Here we argue that the integration of 3D information is a process that may occur over time. In particular, we studied whether the perceptual derivation of slant magnitudes from the optic flow may be affected by the disparity information that has been presented in a previous moment in time. In this experiment, observers were shown two adjacent random-dot stimuli (test and comparison). Two stereograms specifying planar surfaces slanted about the horizontal axis were shown during the first half of the total display duration (1 sec). After 500ms, the random-dots presented to one eye where replaced by a blank field, and the random-dots presented to the other eye were animated so as to produce constant optic flows specifying planar surfaces rotating in depth about the horizontal axis. The observers' task was to compare the slant specified by the optic flow fields in the test and comparison stimuli. The slants defined by disparity information for each test-comparison pair took on the following values: 0–0, 45–45, 0–45, 45–0 degrees; the ratio between test and comparison optic-flow gradients took on the following values: 0.8, 0.9, 1.0, 1.1, 1.2. We found that the psychometric functions indicating the percentage of ‘test more slanted' responses as a function of the optic-flow gradient ratio were unbiased for the 0-0 and 45-45 stereo-defined pairs, whereas they were affected by a systematic bias in the other two experimental conditions. These results therefore reveal that the processing of the optic flow can be affected by stereo information presented in a previous moment in time.