Outer cover where light first passes through - helps focus light rays
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Pupil
Small adjustable opening in the iris
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Iris
muscles that dilate/restrict pupil - responds to light intensity or emotions
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Lens
focuses light into an image projected onto retina - image is reversed (but is later unreversed in the brain)
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Retina
- the light-sensitive inner surface of eye - 3 layers of nerve cells (photoreceptors, interneurons, afferent cells) - transduces light into neural signals
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Fovea
Tiny pit filled with cones - responsible for sharp vision
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Optic Nerve
thick rope of intertwined ganglion axons - carries messages to brain
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Blind Spot
area without visual receptors because it's where blood vessels and nerves connect to eyeball
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1) Photoreceptor Cells
- First layer of retina - rods and cones - transduces light (distal stimulus) into neural signal (proximal stimulus)
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Rods
- a type of photoreceptor cell - detect black and white - peripheral vision - dim light (nighttime)
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Rods
What kind of photoreceptor cell works best at night?
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Rods
what kind of photoreceptor cell is responsible for peripheral vision?
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Cones
- a type of photoreceptor cell - sensitive to red, green, or blue - works best in daytime - detailed vision
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Cones
What kind of photoreceptor cells work best at daytime/in bright light?
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Cones
What kind of photoreceptor cells are responsible for detailed vision?
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2) Bipolar Cells
- Second layer of retina - specialized interneurons - connect photorecptors to ganglion cells
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3) Ganglion Cells
- third layer of retina - specialized afferent neurons - have long axons that intertwine
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Visual Cortex in Occipital Lobe
Final Destination of visual neural message?
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Trichromatic Theory
“there are only 3 types of photoreceptors, so we can only see red, green, and blue”
BUT
“when combined, these photoreceptors allow us to see ALL colors of light”
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Opponent-Process Theory
“2 sets of firing neurons that work in opposite ways”
\ ex. see blue → blue cones fire → neurons connected to those blue cones fire (excitatory messages) while orange gets suppressed (inhibitory messages)
\ evidence: afterimage (seeing opposite colors after staring at a color for awhile)
\ when excitatory signal disappears, the inhibitory briefly overshoots (out of balance)
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Light Adaptation
adjusting to brighter light
* squinting and our pupils constricting
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Dark Adaptation
adjusting to dimmer light
* pupils dilate quickly
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Near-sightedness
people can only see what’s near their eyes
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Far-sightedness
distant objects are clearer and near objects are blurry
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Cataracts
cloudy lenses
* easily removed with surgery
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Glaucoma
excess fluid in eye presses on optical nerve so it can’t fire
* pressure
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Color blindness
* usually in males * red-green
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blindness
can be result of damage to eye, neurons, or visual cortex