Sex and Vision II: Color Appearance of Monochromatic Lights.

This study investigates sex differences in color appearance of monochromatic lights across the visible spectrum, focusing on basic visual functions rather than higher cognitive processes. Testing young adults with normal vision (excluding color-deficient individuals), we used equi-luminant, foveally-viewed flashes against a dark background, measuring hue and saturation via magnitude estimation with language-independent terms (red, yellow, green, blue). Results reveal small but significant differences: males required slightly longer wavelengths (e.g., shifted 2-5 nm) to perceive the same hue as females across nearly all tested wavelengths. Males also exhibited poorer wavelength discrimination in the mid-spectrum, though unique hue loci (R, Y, G, B) showed no correlation with cone sensitivities or paired hue relationships. These differences persisted across Newtonian and Maxwellian optics. We propose that testosterone, abundant in cerebral cortex receptors, influences embryonic development of neural connectivity from the lateral geniculate nucleus (LGN) to primary visual cortex, altering how chromatic inputs are recombined and weighted. This suggests sex-specific neural processing underlies the observed variations in color appearance, complementing our prior findings on spatio-temporal vision differences.