Texture segregation in chromatic element-arrangement patterns.

An element-arrangement pattern is composed of two types of elements arranged differently in different regions of a pattern. Rapid texture segregation depends on spontaneously discriminating the difference in the arrangement of the elements. Five experiments investigated the perceived segregation of patterns composed of two types of squares arranged in vertical stripes in the top and bottom regions and in a checkerboard arrangement in the middle region. The squares were either equal in luminance and different in hue or equal in hue and different in luminance. The rated similarities of the two hues in a pattern failed to predict perceived segregation. For a given background luminance, the perceived segregation was predicted by the square-root of the sum of the squares of the differences in the outputs of the L - M + S and L + M - S opponent channels, where L, M, and S were the cone contrasts of the long-, medium-, and short-wavelength receptors. The perceived similarity of the two hues in a pattern was not affected by the background luminance but was a function of cone excitations instead. For patterns differing in hue and equal in luminance, perceived segregation was an inverse function of the background luminance. A white background decreased the perceived segregation, but a black background did not. The effect of background luminance was not on the discrimination of the individual hues. The two hues making up a texture pattern were clearly distinguishable on a white background. A white background interfered with the discrimination of the vertical and diagonal columns of squares that distinguished the texture regions. For patterns differing in luminance and equal in hue, black and white backgrounds decreased the perceived segregation. The results indicate that adapting to an achromatic luminance distant from the luminance of the squares increased the Weber threshold for discriminating luminance differences, but did not increase the Weber threshold for discriminating hue differences. The experiments also revealed that luminance was the primary factor affecting perceived segregation and that perceived brightness is secondary. The results are consistent with the hypothesis that perceived segregation in element-arrangement patterns is primarily a function of the differences in the outputs of relatively early filtering mechanisms that encode pattern differences prior to the specification of the element shapes and their properties.