Which statement accurately describes the trichromatic theory and its limitation?

Which statement accurately describes the trichromatic theory and its limitation?

• A. It posits two types of photoreceptors for red and green; limitation is color constancy.
• B. It posits four types of cones for RGBW; limitation is color constancy.
• C. It posits three types of cones sensitive to red, green, blue; limitation: cannot explain afterimages and color-opponent processes.
• D. It posits a single photoreceptor type; limitation is poor color discrimination.

Answer: (C)

Color vision starts with three kinds of cones in the retina, each tuned to a different part of the spectrum. The brain creates color perceptions by comparing how strongly each cone type is activated. This is the essence of the trichromatic idea: three cone types—sensitive to long (red), medium (green), and short (blue) wavelengths—and color is determined by the pattern of their activity. The best statement captures both the receptor basis and its main limitation. It correctly identifies three cone types corresponding to red, green, and blue, and explains that color is coded by the relative activity of these cones. The limitation it points to—why this theory can’t fully account for what we experience—focuses on afterimages and the presence of color-opponent processes. After adapting to a color, our sensory system tends to produce an afterimage in the complementary color, a phenomenon better explained by opponent-process processing in the brain (red-green and blue-yellow channels) that comes after the initial cone responses. So, while the trichromatic theory accounts for how receptors detect colors, it doesn’t fully explain these post-receptor processing effects. Briefly, the other ideas don’t fit because they misstate the basic anatomy or omit a key processing step: there aren’t only two or four cone types, there isn’t a single photoreceptor type governing color, and color constancy is a related, but separate, phenomenon not the central limitation described here.

Color vision starts with three kinds of cones in the retina, each tuned to a different part of the spectrum. The brain creates color perceptions by comparing how strongly each cone type is activated. This is the essence of the trichromatic idea: three cone types—sensitive to long (red), medium (green), and short (blue) wavelengths—and color is determined by the pattern of their activity.

The best statement captures both the receptor basis and its main limitation. It correctly identifies three cone types corresponding to red, green, and blue, and explains that color is coded by the relative activity of these cones. The limitation it points to—why this theory can’t fully account for what we experience—focuses on afterimages and the presence of color-opponent processes. After adapting to a color, our sensory system tends to produce an afterimage in the complementary color, a phenomenon better explained by opponent-process processing in the brain (red-green and blue-yellow channels) that comes after the initial cone responses. So, while the trichromatic theory accounts for how receptors detect colors, it doesn’t fully explain these post-receptor processing effects.

Briefly, the other ideas don’t fit because they misstate the basic anatomy or omit a key processing step: there aren’t only two or four cone types, there isn’t a single photoreceptor type governing color, and color constancy is a related, but separate, phenomenon not the central limitation described here.