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In a preferential looking experiment, identical patterns (vertical stripes) were presented to both eyes on one of two screens while orthogonal patterns (vertical stripes in one eye and horizontal stripes in the other) were presented on the other screen. Most infants younger than 3.5 months of age originally showed a preference for the dichoptic (interocularly orthogonal) pattern. At an average age of 3.5 months, however, they showed a sudden shift of preference from this pattern to the interocularly identical pattern. The full shift from a preference for one stimulus to the other (both statistically significant) occurred within a few weeks in most cases. The onset age of the shift in preference agreed with the onset age of fusion-rivalry discrimination found in a previous study (Birch et al., 1985). The original preference for the bincularly orthogonal patterns may be interpreted as a preference for a grid (interocularly emergent intersections) over a grating, judging from results of two control experiments. These data suggest that the pre-stereoptic system non-selectively combines information from the two eyes without regard to edge orientation because it loses eye-of-origin information at a relatively early stage of binocular visual processing. Thus, the pre-stereoptic system does not have the capability of interocular suppression. The theoretical and clinical significance of the new findings are discussed along with a neuronal model of cortical development of ocular segregation and binocular pathways.

Summary The results confirm the conclusion, drawn from studies of the orientation-contingent color AE (McCollough effect), that information about combined color and edge orientation is initially processed separately in monocular channels. It does, however, converge on binocular channels, at least at the level of processing for stereoscopic depth. Other investigators have been unable to demonstrate a depth-specific color AE after binocular adaptation to red and green gratings producing different stereoscopic depths, which fspresumably should adapt color selective binocular channels if they exist (Brown, Stromeyer and Dawson. 1974). These findings suggest that the binocular channels themselves are not selective for color, even though they receive information from monocular channels which are color selective. Taken together, present knowledge drawn from psychophysical research implies that the linkage between color and edge orientation processors occurs prior to and not in binocular channels.