Traditional color vision theory posits that three types of retinal photopigments transduce light into a trivariate neural color code, thereby explaining color-matching behaviors. This principle of trichromacy is in need of reexamination in view of molecular genetics results suggesting that a substantial percentage of women possess more than three classes of retinal photopigments. At issue is the question of whether four-photopigment retinas necessarily yield trichromatic color perception. In the present paper, we review results and theory underlying the accepted photoreceptor-based model of trichromacy. A review of the psychological literature shows that gender-linked differences in color perception warrant further investigation of retinal photopigment classes and color perception relations. We use genetic analyses to examine an important position in the gene sequence, and we empirically assess and compare the color perception of individuals possessing more than three retinal photopigment genes with those possessing fewer retinal photopigment genes. Women with four-photopigment genotypes are found to perceive significantly more chromatic appearances in comparison with either male or female trichromat controls. We provide a rationale for this previously undetected finding and discuss implications for theories of color perception and gender differences in color behavior.

A space-variant optical correlator whose output depends on both the shape and the position of the input signal is introduced. This positionally sensitive correlator has potential applications in machine vision, cryptography, and optical logic. In this approach the input function undergoes a free-space Fresnel transform (which introduces the positional sensitivity) and is multiplied by an appropriate mask function. The Fourier transform of the product then obtains the desired output. The theoretical basis for the space-variant correlator, computer-simulated outputs, and experimental results for the case in which the mask is written onto a magneto-optic spatial light modulator are discussed.

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