Orientation discrimination of motion-defined gratings.

Spatial boundaries can be defined by discontinuities in motion. However, several types of motion contrast exist, each corresponding to the involvement of different spatio-temporal cues. We examined the contribution of two motion cues: a difference in direction of motion (relative motion) and a dynamic occlusion cue. We measured just noticeable differences in the orientation of boundaries defined by one or both of these visual cues. Just noticeable differences in orientation were similar to those reported for luminance gratings, and the presence of two cues in place of one, lowered the thresholds. These results show that relative motion as well as dynamic occlusion can yield precise spatial boundary information.