Editing Afterimage (section)

==Negative afterimages==
[[Negative image|Negative]] afterimages are generated in the retina but may be modified like other retinal signals by [[neural adaptation]] of the [[retinal ganglion cell]]s that carry signals from the [[retina]] of the eye to the rest of the brain.<ref>{{cite journal |last1=Zaidi|first1= Q.|last2= Ennis|first2= R.|last3= Cao|first3= D.|last4= Lee|first4= B. |title=Neural locus of color afterimages. . |journal=Current Biology |date=2012 |volume=22 |issue=3 |pages=220–224 |doi=10.1016/j.cub.2011.12.021 |pmid=22264612 |pmc=3562597 |bibcode=2012CBio...22..220Z |url=https://doi.org/10.1016/j.cub.2011.12.021 |access-date=17 October 2022|hdl=11858/00-001M-0000-000F-4AA5-4 |hdl-access=free }}</ref>

Normally, any image is moved over the retina by small eye movements known as [[microsaccade]]s before much adaptation can occur. However, if the image is very intense and brief, or if the image is large, or if the eye remains very steady, these small movements cannot keep the image on unadapted parts of the retina.

Afterimages can be seen when moving from a bright environment to a dim one, like walking indoors on a bright snowy day. They are accompanied by neural adaptation in the occipital lobe of the brain that function similar to [[color balance]] adjustments in photography. These adaptations attempt to keep vision consistent in dynamic lighting. Viewing a uniform background while adaptation is still occurring will allow an individual to see the afterimage because localized areas of vision are still being processed by the brain using adaptations that are no longer needed.

The [[Young–Helmholtz theory|Young-Helmholtz trichromatic theory]] of color vision postulated that there were three types of photoreceptors in the eye, each sensitive to a particular range of visible light: short-wavelength cones, medium-wavelength cones, and long-wavelength cones. Trichromatic theory, however, cannot explain all afterimage phenomena. Specifically, afterimages are the complementary hue of the adapting stimulus, and trichromatic theory fails to account for this fact.<ref name=Horner>{{Cite book
| author-last = Horner| author-first = David. T.
| date = 2013
| chapter = Demonstrations of Color Perception and the Importance of Colors
| editor1-last = Ware| editor1-first = Mark E.
| editor2-last = Johnson| editor2-first = David E. 
| title = Handbook of Demonstrations and Activities in the Teaching of Psychology
| publisher = Psychology Press
| isbn = 978-1-134-99757-2
| volume = II: Physiological-Comparative, Perception, Learning, Cognitive, and Developmental
| pages = 94–96
| url = https://books.google.com/books?id=iVUnAAAAQBAJ
| access-date = 2019-12-06
}} Originally published as: {{Cite journal
| last = Horner| first = David T.
| date = 1997
| title = Demonstrations of Color Perception and the Importance of Contours
| journal = Teaching of Psychology
| volume = 24
| issue = 4
| pages = 267–268
| issn = 0098-6283
| doi = 10.1207/s15328023top2404_10
| s2cid = 145364769
}}</ref>

The failure of trichromatic theory to account for afterimages indicates the need for an [[opponent process|opponent-process theory]] such as that articulated by [[Ewald Hering]] (1878) and further developed by Hurvich and Jameson (1957).<ref name=Horner/> The [[opponent process]] theory states that the human [[visual system]] interprets color information by processing signals from cones and rods in an antagonistic manner. The opponent color theory is that there are four opponent channels: red versus cyan, green vs magenta, blue versus yellow, and black versus white. Responses to one color of an opponent channel are antagonistic to those of the other color. Therefore, a [[green]] image will produce a [[magenta]] afterimage. The green color adapts the green channel, so they produce a weaker signal. Anything resulting in less green is interpreted as its paired primary color, which is magenta (an equal mixture of red and blue).<ref name=Horner/>