How do red-green opponent receptive fields help detect colour boundaries?

Red-green opponent receptive fields play a critical role in vision by enhancing the detection of colour boundaries. These receptive fields are organized in a concentric manner, where the centre and the surrounding area exhibit opposite, or opponent, responses to specific wavelengths of light.1

This organization helps detect colour boundaries through the following mechanisms:

• Emphasis of Differences: Because the centre and surround have opponent responses—such as an on-response to red in the centre and an off-response to green in the periphery—the system effectively cancels out uniform stimulation. However, when a boundary between two colours moves across the field, the inhibitory and excitatory effects no longer balance, allowing the retina to emphasize the contrast at that edge.1
• Dynamic Sensitivity: This process is bolstered by small, involuntary eye movements, which ensure that boundaries are continually shifting across these receptive fields, thereby maintaining high sensitivity to spatial colour changes.1
• Signal Efficiency: By cancelling out the effects of diffuse white light, this "opponence" keeps the retina "quiet," preventing the optic nerve from being overwhelmed by redundant information and allowing the system to focus on meaningful chromatic transitions.1