Practice improves adults' sensitivity to diagonals.

Adults who were initially less sensitive to a diagonal, 10 c/deg sinusoidal grating, practiced detecting it for 3000 yes-no signal detection trials. Following practice all observers had improved their relative sensitivity to the diagonal and most were as sensitive to the diagonal as to cardinal (horizontal or vertical) orientations. Practicing a cardinal axis, on the other hand, caused no improvement in sensitivity unless the pre-practice threshold for that orientation was elevated with respect to other orientations. Three hypotheses are proposed to account for the improved sensitivity. The results are also related to the typical pattern of adult anisotropic contrast sensitivity which favors the cardinal orientations.