In humans and other primates, sensory signals from each eye remain separated until they arrive in the primary visual cortex (V1), but their exact meeting point is unknown. In V1, some neurons are activated by stimulation of only one eye (monocular neurons) while most neurons are driven by stimulation of either eye (binocular neurons). Monocular neurons are most prevalent in the main input layers of V1 while binocular neurons dominate the layers above and below. This observation has given rise

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... the idea that the two eyes' signals remain separate until they converge outside V1's input layers. Here, we show that despite responding to only one eye, monocular neurons in all layers, including the input layers, of V1 discriminate between stimulation of their driving eye alone and stimulation of both eyes. This finding suggests that binocular signals occur at an earlier processing stage than previously appreciated as even so-called monocular neurons across all V1 layers encode what is shown to both eyes.