3.2 VISION 70% of your receptor cells are in your eyes taste and touch need direct contact where as sight and smell don’t Sight can be experienced from farthest distance

VISION Draw the diagram of the eye above and label each part (hint: use color to distinguish different parts of the eye)

THE VISUAL SYSTEM Cornea Transparent protective coating over the front of the eye Pupil Small opening in the iris through which light enters the eye Iris Colored part of the eye

THE VISUAL SYSTEM Lens Focuses light onto the retina, is transparent and changes shape to focus on things at different distances Retina Lining of the eye containing receptor cells that are sensitive to light Fovea Center of the visual field, images are in sharpest focus here

DIAGRAM Create a diagram showing the path of light from a subject through the different parts of the eye, ending at the optic nerve.

RECEPTOR CELLS IN THE EYE Cells in the retina that are sensitive to light Light- small segment of electromagnetic spectrum to which our eyes are sensitive. Visual receptors are called rods and cones

RECEPTOR CELLS Rods About 120 million rods Respond to light and dark Very sensitive to light Provide our night vision Dominant outside of fovea Cones About 8 million cones Respond to color as well as light and dark Work best in bright light Found mainly in the fovea Both get sparse as you move away from the fovea at the back of the eye.

RECEPTOR CELLS Bipolar cells Receive input from receptor cells(rods/cones) Only have one axon and dendrite In fovea, cones usually only connect to ONE bipolar cell Elsewhere, several rods/cones share a single cell

RECEPTOR CELLS Ganglion cells Receive input from bipolar cells Axons of these join to form optic nerve that carries messages to the brain Cells summarize and organize information for the brain

RECEPTOR CELLS Blind spot Area where axons of ganglion cells leave the eye No receptor cells Even when light from a small object is focused directly on the blind spot, the object will not be seen Pg. 101 test

RECEPTOR CELLS Visual acuity- ability to distinguish fine details visually Pg. 101 x test

FROM EYE TO BRAIN Optic nerve Made up of axons of ganglion cells carries neural messages from each eye to brain Optic chiasm Point where part of each optic nerve crosses to the other side of the brain

ADAPTATION Dark adaptation Increased sensitivity of rods and cones in darkness Usually only see in grey scale, little color Reason for many accidents at night Light adaptation Decreased sensitivity of rods and cones in bright light Squint to reduce amount of light striking your retina Within a minute you usually fully adapt Afterimage Sense experience that occurs after a visual stimulus has been removed Light experiment

FEATURE DETECTORS Feature detectors- specialized brain cells that only respond to particular elements in the visual field such as movement or lines of specific orientation. Cortical blindness- severe damage to visual cortex Blightsight-they behave as if they can see forms, colors, and motion– even though they cannot see Blightsight Ex. Patient might duck if an object is thrown at her, even though she reports not having seen it; she might turn her head toward a bright flashing light although she can’t see it.

COLOR VISION Properties of color Hue – refers to colors such as red and green Most people can identify about 150 hues Saturation – refers to the vividness of a hue Brightness – the nearness of a color to white

THEORIES OF COLOR VISION Additive color mixing Mixing of lights of different hues to create new hues Each light adds additional wavelengths to the over all mix Lights, T.V., computer monitors (RGB) Subtractive color mixing Mixing pigments, e.g., paints, each of which absorbs some wavelengths of light and reflects others

THEORIES OF COLOR VISION Trichromatic theory Three different types of cones Red Green Blue-violet Experience of color is the result of mixing of the signals from these receptors Can account for some types of colorblindnesscolorblindness

FORMS OF COLORBLINDNESS Approximately 10% of men and 1% of women have some form of colorblindness Dichromats People who are blind to either red-green or blue-yellow Monochromats People who see no color at all, only shades of light and dark Tests ?v=yEIM4jmK1F0 ?v=yEIM4jmK1F0

THEORIES OF COLOR VISION Trichromatic theory cannot explain all aspects of color vision People with normal vision cannot see “reddish-green” or “yellowish-blue” Color afterimages

THEORIES OF COLOR VISION Opponent-process theory Three pairs of color receptors Yellow-blue Red-green Black-white Members of each pair work in opposition Can explain color afterimages Both theories of color vision are valid

COLOR VISION IN OTHER SPECIES Other species see colors differently than humans Most other mammals are dichromats Rodents tend to be monochromats, as are owls who have only rods Bees can see ultraviolet light