Editing Stimulus modality (section)

===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>