A psychophysical dissection of the brain sites involved in color-generating comparisons.

We have used simple psychophysical methods to determine the sites of color-generating mechanisms in the brain. In our first experiment, subjects viewed an abstract multicolored "Mondrian" display through one eye and an isolated patch from the display through the other. With normal binocular/monocular viewing, the patch has a different color when viewed on its own (void mode) or as part of the Mondrian display (natural mode) [Land, E. H. (1974) Proc. R. Inst. G. B. 49, 23-58]. When the two stimuli were viewed dichoptically, with the patch occupying the position that it would occupy in the Mondrian complex under normal viewing, the patch always appeared in its void color. In a second experiment, when subjects viewed multicolored displays through a different narrow-band filter placed over each eye, the information from the two eyes was combined to result in new colors, which were not seen through either of the two eyes alone. Taken together, these results dissect color-generating mechanisms into two stages, located at different sites of the brain: The first occurs before the appearance of binocular neurons in the cortex and compares wavelength information across space, whereas the second occurs after the convergence of the input from the two eyes and synthetically combines the results of the first.