Purpose: To investigate the temporal and spatial properties of simultaneous and sequential stereo slant discrimination.

Methods: Stereo-slant discrimination was tested using random dot patterns (V 1.5 x H 8 deg). Yaw-slant was produced by horizontal magnification of one ocular image. Reference and test target patches were presented either simultaneously (stimulus onset asynchrony, SOA=0) or sequentially (SOA>0) for durations of 83 msec and 167 msec. SOA ranged from 0 to 1333 msec. The reference patch was presented at the fixation spot in the screen center and the test patch was either presented 1.5, 2.5, or 4.5 degrees above the reference. In some trials, the test stimulus was presented on a 5 to 10 arc min disparity pedestal from the vertical horopter.

Results: For adjacent targets, slant discrimination thresholds were lowest when SOA=0 (simultaneous condition) and thresholds were highest for sequential slant discrimination with the shortest SOA (83 msec, temporal masking). Threshold was reduced as SOA increased beyond 83 msec reaching a minimum at 333 msec. With longer SOAs up to 1333 msec thresholds increased from the minimum by 20%. Similar results were obtained with both stimulus durations (83 msec and 167 msec). Temporal masking was eliminated either by presenting the test target on a disparity pedestal or separating adjacent edges of the two targets by more than 0.5 degrees.

Conclusion: SOA rather than stimulus duration determines the threshold elevation for slant discrimination, in accordance with previous masking studies (Breitmeyer, 1984; Butler and Westheimer, 1978). The range of stereo slant masking is limited in time, space and disparity. Normal saccadic gaze shifts would not elevate slant discrimination thresholds with temporal masking because the combined latency and duration of a saccade is larger than the longest SOA that is associated with masking.

Supported by NEI grant EYO 8882.