Which factor remains constant within the same cone type, limiting single-cone color discrimination?

Which factor remains constant within the same cone type, limiting single-cone color discrimination?

• A. Absorption rate
• B. Photopigment density
• C. Bleaching rate
• D. Intracellular signaling speed

Answer: (A)

The main idea is that color perception relies on comparing signals from cones with different spectral sensitivities. A single cone type uses the same photopigment, so the probability that photons are absorbed by that pigment is fixed for that type. Under a given light, the absorption rate of that pigment is essentially the same from one cone of that type to another, so the cone’s response reflects overall brightness rather than hue. Since hue information requires differential inputs across multiple cone types, a single cone type cannot distinguish colors on its own. The other factors (how fast bleaching happens, how quickly the intracellular cascade proceeds, or how pigment density varies) don’t impose the same fundamental single-cone color limitation.

The main idea is that color perception relies on comparing signals from cones with different spectral sensitivities. A single cone type uses the same photopigment, so the probability that photons are absorbed by that pigment is fixed for that type. Under a given light, the absorption rate of that pigment is essentially the same from one cone of that type to another, so the cone’s response reflects overall brightness rather than hue. Since hue information requires differential inputs across multiple cone types, a single cone type cannot distinguish colors on its own. The other factors (how fast bleaching happens, how quickly the intracellular cascade proceeds, or how pigment density varies) don’t impose the same fundamental single-cone color limitation.