What does the Principle of Univariance state?

The Principle of Univariance is fundamental to understanding how phototransduction occurs in photoreceptors within the visual system. This principle states that the response of a photopigment to light is only determined by the number of photons absorbed, without regard to the specific wavelength of the light. Essentially, once a photon is absorbed, the photopigment undergoes a chemical change that contributes to the signal that is sent to the brain, but the signal generated is the same regardless of whether the photon was of a longer or shorter wavelength.

This univariate response means that a single photopigment is unable to differentiate between different wavelengths of light solely based on the response it generates. Hence, two different wavelengths can produce the same response in a photopigment if they contain an identical number of photons. This is why it is necessary to have multiple types of photoreceptors, each with different photopigments sensitive to various spectral ranges, to enable the perception of color and distinguish different wavelengths effectively.

Other options suggest limitations or characteristics of photopigments that do not align with the principle. For example, stating that photopigments respond to only specific wavelengths or can distinguish wavelengths precisely would contradict the idea of univariance, which emphasizes