Orientation-Specific Effects of Patterns of Adapting Light on Visual Acuity*

Inspection of a pattern of horizontal, vertical, or oblique lines differentially affects the visual acuity for test gratings as a function of their orientation. After a horizontal grating is viewed for 1 sec or longer, the resolution threshold for horizontal contours is greater than the threshold for the identification of vertical and obliquely oriented contours. Conversely, prolonged viewing of vertical contours raises the threshold for the identification of vertical lines above those for other orientations. Similar results are found following adapting exposures to left-and right-oblique contours. The differential masking effects are systematic functions of the duration of exposure to the light-and-dark adapting pattern.