Interactions between luminance and colour channels in visual search and their relationship to parallel neural channels in vision

We have compared visual search under conditions that tend to isolate the magnocellular, parvocellular and koniocellular channels of the human visual system. We used isoluminant red-green stimuli that do not modulate short-wavelength sensitive (SWS) cones to isolate the parvocellular pathway, isoluminant SWS-cone isolating stimuli to stimulate only the koniocellular system and addition of small luminance contrasts to selectively activate the magnocellular pathway. We found that in the case of conjunction search, where attentional resources were required, the red-green (parvocellular) system can use accompanying small luminance (magnocellular) signals to improve visual search. On the other hand, when using SWS-cone isolating stimuli to selectively stimulate the blue-yellow (koniocellular) system, addition of similar luminance signals did not increase the efficiency of the serial visual search. The results indicate that S-cone signals may be processed in a separate pathway that does not get converging inputs from the magnocellular pathway. This is unlike the case with the red-green opponent system, which functions more synergistically with the magnocellular system.