Sensation Sensation The Eye Vision Light waves Visible

Sensation

Sensation • The Eye- Vision – Light waves – Visible spectrum- one particular segment of electromagnetic energy that we can see because these waves are the right length to stimulate receptors in the eye.

Vision • Parts of the eye – Cornea – Pupil – Iris – Lens – Retina

Vision • Cornea – Covering on your eye, curved surface bends, or focuses, the waves into a narrower beam • Pupil – Allows light waves to pass into the eye’s interior

Vision • Iris – Muscles that control the amount of light that enters the eye – Pigment • Lens – Curved surface bends, or focuses, light waves into an even narrower beam – Muscles are used to adjust focusing

Vision • Retina – Contain photoreceptors – Begin the process of transduction by absorbing light waves • Transduction- Process in which a sense organ changes physical energy into electrical signals that are sent to the brain

Vision • Normal vision- eyeball is shaped so that objects are focused directly on the retina • Nearsighted-eyeball is too long so that objects are focused at a point in front of the retina • Farsighted- eyeball is too short so that objects are focused slightly behind the retina

Vision • Transduction – Retina has two kinds of photoreceptors • Rods and cones – Rods • Shaped like a rod • Activated by small amounts of light • Allows us to see in dim light, but only black, white, and gray

Vision • Cones – Contain three chemicals that are activated in bright light – Allow us to see color and fine detail • Chemicals generate a tiny electrical force that triggers nerve impulses in ganglion cells

Vision • Nerve impulses travel to the back of the eye through the optic nerve toward the brain • Blind spot – Part of the optic nerve that has no receptors

Vision • Color theory – Tri-chromatic theory • Three kinds of cones in the retina • Contain chemicals, opsins, that correspond to the three primary colors; red, blue, green – Opponent process theory • Retina and thalamus respond to two pairs of colors; red-green and blue-yellow

Vision • Color blindness- Inability to distinguish two or more shades in the color spectrum – Monochromats- total colorblindness • Very rare, only have rods or only on kind of cone – Dichromats- trouble distinguishing red from green • Only have two kinds of cones • Genetic and found mostly in males