The split-brain studies wouldn’t work if the participants were allowed to move their eyes or heads, because then both stimuli could reach both sides of the brain. But as long as a participant stares straight ahead and the presentation of the stimuli is brief, light from the stimulus to the person’s right will impact on the left side of the retina in each eye and only stimulate neural pathways leading to the left visual cortex (red shading in the diagram). And under these special conditions, light from the stimulus to the person’s left will be received on the right side of each retina and stimulate neurons leading only to the right visual cortex (yellow shading in diagram).

The split-brain studies wouldn’t work if the participants were allowed to move their eyes or heads, because then both stimuli could reach both sides of the brain. But as long as a participant stares straight ahead and the presentation of the stimuli is brief, light from the stimulus to the person’s right will impact on the left side of the retina in each eye and only stimulate neural pathways leading to the left visual cortex (red shading in the diagram). And under these special conditions, light from the stimulus to the person’s left will be received on the right side of each retina and stimulate neurons leading only to the right visual cortex (yellow shading in diagram).