What color spot does a patient see when performing Maxwell's spot?

When performing Maxwell's spot, the patient perceives a red spot. This phenomenon occurs due to the interaction between different color sensitivities of the cones in the retina, particularly the long-wavelength sensitive cones (which are responsive to red) and the short-wavelength sensitive cones (which respond to blue light).

In the context of the experiment, a yellow stimulus is presented, which predominantly stimulates the medium and long-wavelength cones. However, the blue light that is simultaneously presented is absorbed by the yellow background, creating a condition where the brain's processing of visual input leads to the perception of a red spot in the central area of the visual field. This demonstrates the concept of color opponent processing in the visual system, where colors can appear differently based on the surrounding context.

The procedure highlights the intricacies of color perception and the way the human visual system interprets varying wavelengths of light, confirming the central role of retinal photoreceptors in color discrimination. Understanding this phenomenon not only helps in comprehending visual perception but also in appreciating how color and visual stimuli can be manipulated to elicit specific perceptual responses.