Contextual effects on fine orientation discrimination tasks.

We examined the influence of context on fine orientation discrimination performance using sinusoidal grating patterns. Discrimination performance was impaired in the presence of modulated surrounds of the same spatial frequency, orientation, and contrast as the center. When center and surround were out-of-phase, separated by a gap of mean luminance, or very different in spatial frequency, performance remained at control levels. When center and surround were in-phase but mismatched in mean luminance, suppression was reduced or eliminated and performance was equivalent to luminance-mismatched control conditions. We speculate that lateral interactions in fine orientation discrimination tasks do not occur between objects that are perceptually distinct.