NO RETINAL EFFERENCE IN HUMANS: AN URBAN LEGEND
Visual attention involves the selective processing of sensory information. Animal model systems long ago demonstrated that such selectivity may be mediated by efferents that proceed from the brain to the eye in order to influence afferent input to the brain. However, such a mechanism seems to be absent from the literature on human visual attention. We here suggest that this omission is the result of an urban legend which holds that there are no retinal efferents in humans. We suggest that this legend exists because mammalian vision in general is degenerate relative to the ancestral vertebrate visual system that is clearly evident in birds. Further, our own work on an ideal animal model system has demonstrated that retinal efferents release neuromodulators that accelerate or delay photoreceptor responses to lights. If the same were true in humans, measurements of retinal response latencies would provide objective quantitative indicators of attention.