Abstract
Yellow targets change to brown when presented in sufficiently bright surrounds. In addition the L/M cone excitation ratio needed to produce a red/green balance shifts between yellow and brown: Yellow requires lower L/M, while brown requires higher L/M. Here we use a dichoptic display to assess the relationship between the yellow/brown hue change and the shift of red-green balance. We presented a 4°-diameter foveal target disk to one eye and a bright or dark contiguous surround annulus (2° width) to either the same eye (MONOCULAR condition) or the opposite eye (DICHOPTIC condition). The target and surround were physically contiguous only under monocular conditions but were perceptually contiguous under both conditions. Observers freely adjusted the luminance and red/green balance of the target to the highest light level at which the target appeared exclusively brown with no percept of yellow and appeared neither reddish nor greenish.
For MONOCULAR conditions, the bright contiguous surround induced brown at higher light levels and with a lower L/M ratio at red/green balance, compared to the dark contiguous surround. However for DICHOPTIC conditions the bright and dark surrounds showed no differences for luminance, unlike the monocular conditions, but continued to show the same difference for red/green balance found in the monocular conditions. This suggests the luminance contrast and red/green balance effects may be controlled by separate mechanisms that occur at different points in the visual pathway. This also demonstrates that red/green balance shifts between yellow and brown can be mediated cortically.
UW Royalty Research Fund Grant #A96870.