Stereopsis with chromatic signals from the blue-sensitive mechanism.

Evidence is presented that the depth seen in dim violet targets superimposed on a bright yellow background is mediated solely by the blue-sensitive mechanism. In forced-choice experiments using these stimuli, observers could discriminate between crossed and uncrossed disparities when the targets were either figural or random dot stereograms. Stereo thresholds for a three bar target whose spatial parameters were adjusted for the B cone mechanism were on the order of 40 sec of arc, a value considerably smaller than the spacing between B cones. With the additional assumption that signals from the blue-sensitive mechanism do not contribute to luminance, these results confirm that purely chromatic signals have access to stereoscopic mechanisms.