Dimensional interaction of hue and brightness in preattentive field segregation

Abstract

The interaction of hue and brightness dimensions during preattentive processing was assessed using a novel task. The method combined the texture segregation task of Beck (1966) with the stimulus manipulations of Garner and Felfoldy (1970). Observers were required to make field segregation judgments for textured visual arrays. Fields were segregated by differences on a single dimension, either hue or brightness. For some arrays the second dimension had a constant level, for others it varied irrelevantly. In Experiment 1, the extent of interaction between hue and brightness dimensions was assessed at two levels of hue discriminability. Irrelevant variation of brightness interfered with segregation judgments based on hue at both levels of hue discrirninability. Hue variation did not interfere with judgments based on brightness at either level. Segregation judgments were longer for both hue and brightness arrays in the hard than in the easy hue discriminability stimulus set. In Experiment 2, all arrays were randomly mixed in an unblocked design to determine whether blocking in Experiment 1 produced a general slowing of response for arrays in the hard discriminability set. An identical pattern of asymmetric interference was revealed. Irrelevant variation of brightness interfered with hue segregation judgments at both discriminability levels. Hue variation did not interfere with judgments based on brightness at either level. In the unblocked design, only hue arrays were influenced by the hue discriminability manipulation. In Experiment 3, diecriminability was reduced for brightness and enhanced for hue. A symmetric pattern, whereby hue variation interfered with brightness judgments and brightness variation with hue judgments, was obtained when hue was easy to discriminate. When hue was difficult to discriminate, only brightness variation interfered with hue judgments. These findings are consistent with the claim that simple properties of the stimulus mediate preattentive boundary judgments (Beck, 1966, 1982; Treisman, 1982). Furthermore, the results show that although the dimensions of hue and brightness can promote field segregation, they are highly susceptible to interference from other dimensions present in the array. © 1984 Psychonomic Society, Inc.