Editing Cone cell (section)

==Function==
[[File:BirdCone.png|thumb|left|[[Bird vision|Bird]], [[reptile|reptilian]], and [[monotreme]] cone cells]]

The difference in the signals received from the three cone types allows the brain to perceive a continuous range of colors through the [[opponent process]] of color vision. [[Rod cells]] have a peak sensitivity at {{val|498|u=nm}}, roughly halfway between the peak sensitivities of the S and M cones.

All of the receptors contain the protein [[photopsin]]. Variations in its conformation cause differences in the optimum wavelengths absorbed.

The color yellow, for example, is perceived when the L cones are stimulated slightly more than the M cones, and the color red is perceived when the L cones are stimulated significantly more than the M cones. Similarly, blue and violet hues are perceived when the S receptor is stimulated more. S Cones are most sensitive to light at wavelengths around {{val|420|u=nm}}. At moderate to bright light levels where the cones function, the eye is more sensitive to yellowish-green light than other colors because this stimulates the two most common (M and L) of the three kinds of cones almost equally. At lower light levels, where only the rod cells function, the sensitivity is greatest at a blueish-green wavelength.

Cones also tend to possess a significantly elevated visual acuity because each cone cell has a lone connection to the optic nerve, therefore, the cones have an easier time telling that two stimuli are isolated. Separate connectivity is established in the
[[inner plexiform layer]] so that each connection is parallel.<ref name="pmid20362067">{{cite journal|last=Strettoi|first=E|author2=Novelli, E |author3=Mazzoni, F |author4=Barone, I |author5= Damiani, D |title=Complexity of retinal cone bipolar cells.|journal=Progress in Retinal and Eye Research|date=Jul 2010|volume=29|issue=4|pages=272–83|doi=10.1016/j.preteyeres.2010.03.005|pmid=20362067|pmc=2878852}}</ref>

The response of cone cells to light is also directionally nonuniform, peaking at a direction that receives light from the center of the pupil; this effect is known as the [[Stiles–Crawford effect]].

S cones may play a role in the regulation of the [[Circadian rhythm|circadian system]] and the secretion of [[melatonin]], but this role is not clear yet. Any potential role of the S cones in the circadian system would be secondary to the better established role of [[melanopsin]] (see also [[Intrinsically photosensitive retinal ganglion cell]]).<ref>{{Cite web |last=Soca |first=R |date=Feb 13, 2021 |title=S-cones and the circadian system |url=https://keldik.com/blogs/sleep-circadian-binnacle/s-cones-and-the-circadian-system |url-status=live |archive-url=https://web.archive.org/web/20210214035406/https://keldik.com/blogs/sleep-circadian-binnacle/s-cones-and-the-circadian-system |archive-date=2021-02-14 |access-date= |website=Keldik}}</ref> 

=== Color afterimage ===
Sensitivity to a prolonged stimulation tends to decline over time, leading to [[neural adaptation]]. An interesting effect occurs when staring at a particular color for a minute or so. Such action leads to an exhaustion of the cone cells that respond to that color – resulting in the [[afterimage]]. This vivid color aftereffect can last for a minute or more.<ref>Schacter, Daniel L. ''Psychology: the second edition.'' Chapter 4.9.</ref>