Contour integration in color vision: a common process for the blue-yellow,red-green and luminance mechanisms?

We compare the performance of the red-green, blue-yellow and luminance post receptoral mechanisms on a contour integration task requiring the linking o f oriented Gabor elements across space to extract a winding 'path' or conto ur. We first establish that for all three mechanisms curvature and contrast are independent; losses in performance due to one cannot be compensated by changes in the other. We then compare contour integration by the three mec hanisms using a method that controls for their differences in cone contrast thresholds. Our results show that despite the poor orientation discriminat ion thresholds and poor spatial sampling found for the blue-yellow mechanis m, all three mechanisms perform similarly on contour integration over a wid e range of curvatures. Furthermore, all three mechanisms have the same depe ndence on path curvature. We also investigate the effects of adding externa l orientation noise. Our results imply that the internal orientation noise for extracting 'aligned' path elements is similar in the three mechanisms a nd for all path curvatures, and the relative efficiencies are also similar for the three mechanisms. To account for our results, we propose that the t hree postreceptoral mechanisms use a common contour integration process. Th is linking process, however, cannot be color-blind; our last experiment sho ws that linking between different chromatic mechanisms or between opposite spatial phases disrupts contour integration. We thus propose that the commo n integration process remains sensitive to the color contrast and phase of its inputs. (C) 2000 Elsevier Science Ltd. All rights reserved.