Toward the development of a color visual prosthesis.

Abstract

<i>Objective</i>. All of the human prosthetic visual systems implanted so far have been achromatic. Schmidt<i>et al</i>(1996<i>Brain</i><b>119</b>507-22) reported that at low stimulation intensities their subject reported that phosphenes usually had a specific hue, but when the stimulus intensity was increased, they desaturated to white. We speculate here that previous B/W prosthetic systems were unnecessarily over-stimulating the visual cortex to obtain white phosphenes, which may be why unexpected alterations in phosphenes and seizures were not an uncommon occurrence. A color prosthesis would have the advantage of being elicited by lower levels of stimulation, reducing the probability of causing epileptogenic responses.<i>Approach.</i>A 'hybrid' mode of stimulation is suggested, involving a combination of B/W and color stimulation, which could provide color information without reducing spatial resolution.<i>Main results.</i>Colors in the real world are spread along intensity and chromatic gradients.<i>Significance.</i>Software implementation strategies are discussed, as are the advantages and challenges for possible color prosthetic systems.