We measured reaction times and hit rates in a 2AFC orientation discrimination task. Gabor patches at different spatial frequencies and two levels of contrast (0.15 and 0.6) were presented surrounded by red, blue, or grey isoluminant backgrounds.. Results revealed lower accuracy and slower reaction times when the gabors were surrounded by red in comparison to blue or grey backgrounds. We interpret these results as evidence that i) exposure to long-wavelength light interferes with both magnocellular and parvocellular processing; but ii) long-wavelength light causes greater relative inhibition of magnocellular processing. These findings are relevant to the interpretation of studies that use red backgrounds to selectively isolate magnocellular contributions, and may have implications for the interpretation of studies of the effect of red contexts on diverse perceptual and cognitive tasks.
