Illustrations of noisy encoding of monochromatic inputs by the cone responses.

<p>On the left is the cone spectral sensitivity (with , where s are derived from the Smith and Pokorny cone fundamentals<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0019248#pone.0019248-Smith1" target="_blank">[15]</a>, the cone density ratio is , the pre-receptor light transmission factors , and Max). A monochromatic input of wavelength evokes response from the three cones, L, M, and S. Due to input noise, there is a range of possible responses from this input. If the mean response to a monochromatic input of nearby wavelength is one of the typical responses within this range of responses to input , then it will be difficult to perceptually distinguish the input from input .</p>