Ch 6: The Visual System
Think about it… The light from the outside world enters your eye and creates a 2-D upside-down image on your retina… Yet somehow, your brain is able to translate it into a complex 3-D representation of the world around you!
Light With no light, there is no vision. Light can be quantified as particles called photons Simultaneously, it is a wave For humans, the visible light spectrum is 380-760nm Other species can see beyond this range Wavelength value dictates the color seen Intensity is related to the brightness of the light
Light Entering the Eye The amount of light entering the eye through the pupil depends on the constriction of the muscles of the iris. The eye will dilate and contract to accommodate for changes in the ambient illumination; balancing sensitivity & acuity.
Light Entering the Eye Sensitivity: ability to detect dimly lit objects Acuity: ability to see the details of objects Must tradeoff between the two Illumination high: Sensitivity not important, constrict pupils & get a sharper image and greater depth of focus Illumination low: Pupils dilate to let available light in, sacrifice depth of focus and acuity
Light Entering the Eye Behind the pupil is the lens, which focuses the incoming light onto the retina. Depending on the distance of the object, the ciliary muscles will adjust the shape of the lens This changes the refraction or bending of the light so it will come into sharp focus on the retina
2 Eyes We have a pair of eyes because, as vertebrates, we have 2 sides. The common set up is to have one eye on each side, which allows the animal to see in most directions without moving their heads. Along with some other animals, we have our eyes positioned front-facing This allows us to have depth perception
2 Eyes http://www.youtube.com/watch?v=WpRAxfI1bpY
2 Eyes The movements of your 2 eyes are coordinated, so that the visual input from each of your eyes comes to the same point on your retina