Abstract

Interference fringes pulsed at constant mean luminance can be detected at spatial frequencies far above the resolution limit. This is due at least in part to aliasing by the receptor mosaic (Williams, Vision Res. 1985), but another possible cue is provided by nonlinear distortion, which can create spatially uniform temporal transients when a pulsed fringe is presented. We have investigated the influence of spatially unstructured distortion products by superimposing the pulsed fringes on a randomly flickering uniform field. As expected, this manipulation has almost no effect on contrast sensitivity well below the resolution limit. Just above the resolution limit, however, the random luminance mask profoundly reduces fringe sensitivity, suggesting that spatially unstructured distortion products provide the basis for detection in this range. At higher fringe frequencies that ap proximately match the cone mosaic, the random luminance flicker again becomes ineffective for some observers. This creates a pronounced secondary maximum in contrast sensitivity in the flicker mask condition, presumably due to spatially structured cues provided by aliasing with the cone mosaic. Apparently in the unmasked case, distortion products bridge the gap between the resolvable frequency range and the aliasing range.

© 1991 Optical Society of America