chap 3 - Chapter 3: The Visual System I. Physical Stimulus...

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Chapter 3: The Visual System I. Physical Stimulus - Wavelength- of a light source refers to the physical distance of a single wave cycle measured from peak to peak. Measured in nanometers o Humans can see from about 380 nm to 760 nm - Psychological effect on intensity is brightness - Illuminance refers to the physical intensity of the light falling on or illuminating a surface - Luminance- intensity of the light reflected from an illuminated surface - 3 major phyla have developed eyes: arthropods, mollusks, and vertebrates II. Anatomy of the Eye - Retina- photosensitive layer - Lens- optical properties cause it to focus an image on the retina - Sclera- outer covering of the eyeball that is a tough, white opaque coat - Cornea- the front of the eye, a translucent membrane o The incoming light rays reflected from the environment must be refracted or bent and brought to focus on the surface at the rear of the eyeball on the retina - Cornea- where refraction begins. Most of the light rays refraction begins here - Choroid- 2 nd layer of eyeball and is attached to the sclera. It consists largely of blood vessels that provide a major source of nutrition for the eye. It is heavily pigmented that enables the absorption of most extraneous light entering the eye - Iris- in the front of the eye, a colored concentric disk o Has 250 distinct physical features o Disk-like colored membrane consisting of 2 smooth muscles that lies between the cornea and the lens o Regulates the amount of light entering the eye When lighting conditions are poor, the iris opens, dilates, to increase the size of the pupil In bright light, the iris closes, constricting the size of the pupil - Pupil- round black opening surrounded by the iris - Whytt’s Reflex- an immediate constriction of the pupil in response to bright light. The inability to demonstrate Whytt’s reflex may indicate neural injury - LENS- divided into 2 chambers o Aqueous humor- small water filled chamber which helps maintain the shape of the eye and provides metabolic requirements of the cornea o Vitreous humor- large chamber behind lens filled with jelly like protein. It holds the lens in place and allows housing to be flexible - Retina- light passes through lens to the retina which covers 200˚ of the inside of the eyeball. Contains 2 types of photoreceptors o Rods- 120-130 million concentrated in peripheral region of retina o Cones- 6-8 million concentrated in fovea - Fovea- contains only cones - Optic Disk- part of the retina where optic nerve fibers leave the eye en route to the brain
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- Blind Spot- created because there are no photoreceptors and no light strikes this portion of the retina III. Neural Connection in Retina - There are vertical and horizontal connections between the photoreceptors and the optic nerce - Bipolar cells- vertical connections between rods and cones (sometimes only cones) and intermediate cells - Ganglion cells- bipolar cells connect to ganglion cells whose axons are optic nerve fibers - There are 2 layers of horizontal connections that link adjacent bipolar and
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This note was uploaded on 04/07/2008 for the course PSYC 3040 taught by Professor Walker during the Spring '08 term at Georgia Institute of Technology.

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chap 3 - Chapter 3: The Visual System I. Physical Stimulus...

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