A contrast paradox in stereopsis, motion detection, and vernier acuity.

Stereoacuity improves with increasing contrast, unless the increase is monocular. In this case performance paradoxically suffers. This study examined whether this contrast paradox occurs for two other classes of visual judgment: two-frame motion and vernier acuity. We constructed three homologous tasks in which the two components of a gabor stimulus (stereo half-images, motion frames, vernier components) were either both high contrast, both low contrast, or mismatched. The contrast paradox was evident in all three tasks and showed a similar spatial frequency dependence. We suggest the contrast paradox results from the combination of mismatched signals by a single filter.