The oblique effects of pattern and flicker sensitivity: implications for mixed physiological input.

The inferior contrast sensitivity for oblique gratings has been previously demonstrated at high spatial frequencies with an absolute criterion. In this study contrast sensitivity at oblique and main axis orientations was obtained under separate pattern and flicker threshold criteria across a range of both spatial and temporal frequencies. The anisotropy of contrast sensitivity was not observed at low spatial frequencies under any stimulus or criterion conditions. At high spatial frequencies the anisotropy was observed for both pattern and flicker thresholds, although the flicker anisotropy was less pronounced. If, as previously suggested, this anisotropy is mediated by X cells, then these psychophysical findings suggest a mixed model in which both pattern and flicker systems receive input from both X and Y-cell pathways.