Editing Stimulus modality (section)

==Light modality==

[[File:Schematic diagram of the human eye en.svg|thumb|Schematic diagram of the human eye.]]

===Description===
The stimulus modality for vision is light; the human eye is able to access only a limited section of the [[electromagnetic spectrum]], between 380 and 760 [[nanometre]]s.<ref name=Russell>{{cite book|last=Russell|first=J.P|author2=Wolfe, S.L. |author3=Hertz, P.E. |author4=Starr, C. |author5=Fenton, M. B. |author6=Addy, H. |author7=Denis, M. |author8=Haffie, T. |author9=Davey, K.   |title=Biology: Exploring the Diversity of Life, First Canadian Edition, Volume Three|year=2010|publisher=Nelson Education|isbn=978-0-17-650231-7|pages=833–840}}</ref> Specific inhibitory responses that take place in the visual cortex help create a visual focus on a specific point rather than the entire surrounding.<ref>{{cite web|last=Yarbrough|first=Cathy|title=Brains response to visual stimuli helps us to focus on what we should see, rather than all there is to see|url=http://www.eurekalert.org/pub_releases/2005-10/si-brt102105.php|work=EurekAlert!|accessdate=29 July 2012}}</ref>

===Perception===
To perceive a light stimulus, the [[eye]] must first refract the light so that it directly hits the [[retina]]. Refraction in the eye is completed through the combined efforts of the [[cornea]], [[lens (anatomy)|lens]] and [[iris (anatomy)|iris]]. The transduction of light into neural activity occurs via the [[photoreceptor cell]]s in the retina. When there is no light, [[Vitamin A]] in the body attaches itself to another molecule and becomes a protein. The entire structure consisting of the two molecules becomes a [[photopigment]]. When a particle of light hits the photoreceptors of the eye, the two molecules come apart from each other and a chain of chemical reactions occurs. The chemical reaction begins with the photoreceptor sending a message to a neuron called the [[bipolar cell]] through the use of an [[action potential]], or nerve impulse. Finally, a message is sent to the ganglion cell and then finally the brain.<ref name=Carlson>{{cite book|last=Carlson|first=N. R.|title=Psychology: The Science of Behaviour|year=2010|publisher=Pearson Education Canada|location=Toronto, Ontario|isbn=978-0-205-64524-4|display-authors=etal|url-access=registration|url=https://archive.org/details/psychologyscienc0004unse}}</ref>

===Adaptation===
The eye is able to detect a visual stimulus when the [[photons]] (light packets) cause a photopigment molecule, primarily [[rhodopsin]], to come apart. Rhodopsin, which is usually pink, becomes bleached in the process. At high levels of light, photopigments are broken apart faster than can be regenerated. Because a low number of photopigments have been regenerated, the eyes are not sensitive to light. When entering a dark room after being in a well lit area, the eyes require time for a good quantity of rhodopsin to regenerate. As more time passes, there is a higher chance that the photons will split an unbleached photopigment because the rate of regeneration will have surpassed the rate of bleaching. This is called [[adaptation (eye)|adaptation]].<ref name=Carlson />

===Colour stimuli===
Humans are able to see an array of colours because light in the visible spectrum is made up of different wavelengths (from 380 to 760&nbsp;nm). Our ability to see in colour is due to three different [[cone cells]] in the retina, containing three different photopigments. The three cones are each specialized to best pick up a certain wavelength (420, 530 and 560&nbsp;nm or roughly the colours blue, green and red). The brain is able to distinguish the wavelength and colour in the field of vision by figuring out which cone has been stimulated. The physical dimensions of colour include [[wavelength]], [[intensity (physics)|intensity]] and purity while the related perceptual dimensions include [[hue]], [[brightness]] and saturation.<ref name=Carlson />

Primates are the only mammals with colour vision.<ref name=Carlson />

The [[Trichromatic theory]] was proposed in 1802 by [[Thomas Young (scientist)|Thomas Young]]. According to Young, the human visual system is able to create any colour through the collection of information from the three cones. The system will put together the information and systematize a new colour based on the amount of each hue that has been detected.<ref name=Carlson />

===Subliminal visual stimuli===
Some studies show that subliminal stimuli can affect attitude. In a 1992 study Krosnick, Betz, Jussim and Lynn conducted a study where participants were shown a series of slides in which different people were going through normal every day activities (i.e. going to the car, sitting in a restaurant). These slides were preceded by slides that caused either positive emotional arousal (i.e. bridal couple, a child with a Mickey Mouse doll) or negative emotional arousal (i.e. a bucket of snakes, a face on fire) for a period 13 [[milliseconds]] that participants consciously perceived as a sudden flash of light. None of the individuals were told of the subliminal images. The experiment found that during the questionnaire round, participants were more likely to assign positive personality traits to those in the pictures that were preceded by the positive subliminal images and negative personality traits to those in the pictures that were preceded by the negative subliminal images.<ref name="KrosnickAndOthers">{{Cite journal| first1 = J. A.| last3 = Jussim | first2 = A. L.| last1 = Krosnick | first3 = L. J.| last2 = Betz | first4 = A. R.| title = Subliminal Conditioning of Attitudes| journal = Personality and Social Psychology Bulletin| volume = 18| issue = 2| pages = 152–162| year = 1992| last4 = Lynn | doi = 10.1177/0146167292182006| s2cid = 145504287 }}</ref>

===Tests===
Some common tests that measure visual health include [[visual acuity]] tests, refraction tests, [[visual field test]]s and colour vision tests. Visual acuity tests are the most common tests and they measure the ability to bring details into focus at different distances. Usually this test is conducted by having participants read a map of letters or symbols while one eye is covered. Refraction tests measure the eye's need for glasses or [[corrective lenses]]. This test is able to detect whether a person may be [[nearsighted]] or [[farsighted]]. These conditions occur when the light rays entering the eye are unable to converge on a single spot on the [[retina]]. Both [[refractive errors]] require corrective lenses in order to cure blurriness of vision. Visual field tests detect any gaps in peripheral vision. In healthy normal vision, an individual should be able to partially perceive objects to the left or right of their field of view using both eyes at one time. The center field of vision is seen in most detail. Colour vision tests are used to measure one's ability to distinguish colours. It is used to diagnose colour blindness. This test is also used as an important step in some job screening processes as the ability to see colour in such jobs may be crucial. Examples include military work or law enforcement.<ref name="vision test">{{cite web|author=Healthwise Staff|title=Vision Tests|url=http://www.webmd.com/eye-health/vision-tests|publisher=WebMD|accessdate=29 July 2012}}</ref>