ON THE EXAM WRITE WADE DR HAWKINS FATHERS NAME ADDS 3 10 29 2013 POINTS EXAM 4 INFORMATION We know the most about vision most researched Value looking at it serves as brain function generally Vision is the only system that has only the CNS no PNS Things going on in vision things going on in the brain Visual system Allows you to consider the transformation of physical stimuli in the environment to language that the brain understands o Transduction way of changing physical stimuli to energy of o Energy being used light o Light is a form of energy that is a part of the electromagnetic the NS spectrum o Electromagnetic spectrum can be used in a dual way Can be thought of as particles of something Can also be considered a continuous waveform rather than discrete packets of energy o Quantum energy If you bombard some materials with energy they emit electrons You can detect electron emission If you crank up energy electrons emitted are done so in packets Portion of the spectrum our eyes can detect photon We can see it Characteristics of vision are characteristics of photons and their light Wave property waves are inverse o Wavelength distance between 2 peaks Ones important to us for vision 400 800 nanometers nM o Frequency How many peaks pass in time Shorter wavelength higher frequency Measured in cycles per second Or Hertz Hz 1 cycle 1 hertz Long wave length low frequency o Bees and other animals can detect other wavelengths that humans cannot All light we see if reflected light something that is changed by the size of the object If wavelengths are longer than 400 800 it will not be reflected will pass right through object If smaller than 400 800 will pass right through us x rays Transparency reflectiveness of the light Not visible to us because it is absorbing Anatomy of the eye Encased in pocket of bone orbit attached to orbit by muscles that allow it to move Muscles are controlled by nerves 3 identifiable layers o 1 Sclera outer layer tissue that in most of the eye is opaque doesn t allow passage of light is really tough Unusual in that in almost all of it white except at the front where it turns into the cornea allows passage of light Prevents penetration of the eye Requiring light to enter the eye only from the front through the cornea Light can be focused on a particular place in the eye can extract placement information from topographic o 2 2nd layer pigment epithelium part of the eye that contains the blood vessels of the eye Only part that contains pigment in the form of melanin Pigment absorbs light Replenishes the blood vessels Anterior pole pigment epithelium contains muscle groups within it Allow eye to be adjusted to change amount of light coming into eye and the focal point of light after it has entered the eye Iris gives eye its color Pupil light is allowed to enter through here If you have a person who has no melanin albino one of the problems poor vision even with contacts due to more light is entering the eye because there is no pigment in the iris No pigment anywhere Light bounces around in the eye Lose topographic information where the light originated In iris there are two muscle layers smooth muscle autonomic system controls it sympathetic Sphincter aiding in focusing of the light As light emitting object gets closer to your face amount of light hitting eye goes up and the divergence of the rays of light o Object approaches eye eye responds by decreasing pupil size allow less light to enter the eye decreasing apture of the pupil acting to filter out diverging rays allows parallel rays o Changing pupil size and luminance is called accommodation Ciliary muscle like sphincter muscle In arrangement Circular Between lenses and cillary muscle there are ligaments Controlled by cranial nerves Object is at a distance cillary muscles are relaxed Tension on ligament is high as object moves closer ligament relaxes Gets pulled all around the edge Object is at distance lens is flat lens is elastic protein material it becomes more rounded when ligament relaxes Accommodation of the lens what all of this is Important for focusing Closer to face pupil is smaller lens is more round Must do this to focus Lens is only tissue in the body that grows by accretion new tissue is added to the outside of the lens New proteins added Layered structure Problem with growth of this type Old tissue is not gotten rid of still there Protein never goes away As lens ages lens becomes more dense less able to get rid of waste and absorb nutrients How you get cataracts Decrease in accommodation in distance By 50 lens no longer changes shape as object gets closer to face Babies can see objects close to their face 3rd layer of eye retina Contains photo detectors Rods and Cones Clear materials that are more dense can slow light down Light waves are being bent refracted Being able to refract light refractive index Simple measure of speed of light in a vacuum over speed of light in the material Speed of light in vacuum speed of light in material EX 300 000 20 000 1 5 refractive index Have to have a refractive index greater than 1 to bend the light slows it down Other key factor in refraction angle at which the light enters Light will be focused on the fovea of the eye Focal point distance between center of lens and focal point is called the focal length Measured in units called diopters 1 diopter is a lens that has a focal length of 1 meter Lens that is stronger 2x have focal length of 2 meters moves it in by half a meter Lens we get for glasses contacts change is diopter strength If you have an object that is approaching your face the rays of light because increasingly divergent As they diverge more they overpower the focal ability of the lens Have to refract light more to 1 Change refractory index make lens more curved Will refract more Want to maintain the focal lens see clearly 2 Lens slow light more change refractive index NOT possible Only thing eye can do is change the curvature of the lens Cornea to fovea has about the same refractive index Difference in speed of light is not very great Most of the strength of the eye comes from the Cornea makes up 80 of the refraction that occurs Lens can add additional power of refraction 18 1st refraction occurs in the outer layer of the cornea cornea Retina Fovea center of the eye Light does strike directly onto the eye Most detailed vision occurs here Made up of many types of cells 3 big ones contained in distinct layers o Ganglion cell layer o Bipolar cell