The distribution of preferred orientations in the peripheral visual field.

Orientation discrimination was measured for line targets in the fovea and in locations along four meridians (vertical, horizontal, 45 degrees and 135 degrees ) in the peripheral visual field. In all locations, the performance for vertical and horizontal contours was on average almost twice as good as for oblique ones. In addition, especially in peripheral locations along oblique meridians, thresholds tend to be better for radially-oriented contours compared to tangential ones. These effects are robust to length of the test lines and to small changes in position and cannot therefore be due to cortical singularities (pinwheels). The results suggest that the advantage of horizontal and vertical contours, as well as possibly of radial ones, is a manifestation of a characteristic structural property of the organization of the visual pathway. Copyright 2002 Elsevier Science Ltd.