The contributions of figure and ground textures to segmentation.

Several models of texture segmentation use spatial gradients in the activity of early filters to locate texture boundaries. The models assume that these filters are identical to those involved in the detection and discrimination of near threshold patterns. The models differ in how activity gradients from different types of filters are combined. We examined this question by measuring the respective contributions of a figure and a ground texture to segmentation. Vertical and horizontal line segments were used to construct two perfectly discriminable textures and these textures were used to construct four types of displays. Each display contained an obliquely oriented figure, but the displays differed in the way this figure was defined. Displays consisted of either (1) a horizontally textured figure on a blank background, (2) a blank figure on a vertically textured background, (3) a horizontally textured figure on a vertically textured background or (4) a figure with a mixed texture (50% vertical lines, 50% horizontal lines) on a blank background. In a two-alternative forced-choice experiment, observers were asked to judge the figure's orientation (right or left oblique), and the contrast of the textures was varied across trials. The resulting psychometric functions for segmentation were very similar for the four types of displays, suggesting ways in which a simple model of segmentation should be modified.