INFLUENCE OF BOUNDARY INFORMATION ON THE PERCEPTION OF COLOR

The integration of color and form to produce a unified percept is a ce ntral problem in vision research. We know that the spatial arrangement of colored stimuli influences their detectability. In the gap effect, for example, a small gap between two colored fields enhances their di scriminability [Opt. Acta 24, 159 (1977)]. Chromatic thresholds are al so reduced when test fields are spatially demarcated. To explore the m echanisms underlying these types of effect, the influence of spatial s tructure on chromatic sensitivity for gratings was measured. For sine- wave and square-wave gratings modulated in different directions in col or space,:contrast sensitivity was measured by using a two-alternative forced-choice procedure with a QUEST staircase. Thin lines, of the sa me orientation as that of the grating, were superimposed on it at half -cycle intervals. The phase of the superimposed lines was varied. For S-cone modulated gratings; dark lines placed at-the mid-points between peaks and troughs (90 degrees) increased sensitivity. As the phase of the lines moved toward the peaks (0 degrees), their effect on sensiti vity declined to zero. A similar but smaller effect was seen for isolu minant L- and M-cone modulated gratings. The superimposed lines always impaired contrast sensitivity for achromatic gratings, especially at a phase of 0 degrees. Spatial structure superimposed on gratings can b oth facilitate and impair contrast sensitivity. In the presence of sha rp boundaries, chromatic sensitivity is increased. This effect may dep end more on the salience of boundaries, since isoluminant lines superi mposed on S-cone modulated gratings and gray lines of similar cone con trast can facilitate detection if they are of sufficient contrast. Ach romatic contrast sensitivity is reduced when the boundaries are presen t. The additional luminance information at the boundaries masks the gr ating. A simple model in which spatial integration is arrested at the positions of the superimposed lines fits only the isoluminant conditio ns. For both luminance and chromatic contrast the change in sensitivit y depends on phase. (C) 1997 Optical Society of America.