Orientation Discrimination for Bars Defined by Orientation Texture

Abstract

A texture pattern consisting of short (0.2 deg) lines contained a 5.0 deg × 1.4 deg texture-defined bar. The bar was rendered visible by the difference in orientation (2θ) between the lines inside the bar and outside the bar. Orientation-discrimination threshold for the texture-defined bar was a U-shaped function of 2θ over the range 2θ = 0° to 2θ = 180°. The lowest threshold was at 2θ = 90°, and was 0.57° for both subjects tested. This threshold was little different from the lowest values of threshold for motion-defined bars, disparity-defined bars, and colour-defined gratings reported elsewhere. A luminance-defined bar was created by switching off all texture lines outside the texture-defined bar. Orientation-discrimination threshold fell to a limiting value as the luminance contrast of this bar was progressively increased. The lowest value of orientation discrimination for the luminance-defined bar (0.42° and 0.35° for the two subjects) was not greatly less than the lowest value for the texture-defined bar.