The<unk>  is how one can discriminate between wavelengths through comparison of multiple photoreceptors. The<unk>  states that one and the same visual receptor cell can be excited by different combinations of wavelength and intensity, so that the brain cannot know the color of a certain point of the retinal image. One individual photoreceptor type can therefore not differentiate between a change in wavelength and a change in intensity. Thus the wavelength information can be extracted only by comparing the responses across different types of receptors. The<unk>  was first described by W. A. H. Rushton (p. 4P). Both cone monochromats (those who only have 1 cone type) and rod monochromats (those with no cones) suffer from the<unk> . The<unk>  can be seen in situations where a stimulus can vary in two dimensions, but a cell's response can vary in one. For example, a colored light may vary in both wavelength and in luminance. However, the brain's cells can only vary in the rate at which action potentials are fired. Therefore, a cell tuned to red light may respond the same to a dim red light as to a bright yellow light. To avoid this, the response of multiple cells is compared.
Principle of univariance
Biological determinism
Confidentiality
Precautionary principle
Theory of indispensable attributes
Efficiency–thoroughness trade-off principle
Information-theoretic death
Biological inequity