2 - Vision Flashcards
Back of Eye
- Sclera: White of eye; thick - gives structure
- Choroid - blood vessel layer
- Retina- inner layer, back of eye, photoreceptors, leads to optic nerve
- Cats- tapida lucidum- green eyes- reflective layer
- Red eye phenomena- bright flash, see vasculature
Front of Eye
- Cornea- front, clear- contact lens goes here, light enters here- refract/focus into lens
- Iris- colored part of eye, PAIR of muscles: dilator pupillae & constrictor pupillae
- Lens- behind iris, refracts light into retina
Anterior chamber- in front of iris
Posterior chamber- in front of lens, behind iris- makes aqueous humor (specifically ciliary body)
- Canal of Schlemm- allows aqueous humor (front, clearer than vitreous) to drain out
- –if blocked, at risk of GLAUCOMA (eye pressure = damage optic nerve)
Middle of eye
- Ciliary muscles- attached to lens via zonular fibers/suspensory ligaments- stretch/constrict lens to focus light in dif ways- near vs far
- —as you get older, lens stiffer + muscles don’t work as well = farsightedness, harder reading = bifocals; presbyopia
-Vitreous humor = behind lens; transparent gel; eye shape + support retina—— look at neutral background, squiggles floating around in vision- floaters = bits of protein/cells- harmless, float around in v. humor
Path of info into eye
- Lens refraction- inverted image projected onto retina
- the brain does NOT receive an inverted image and flip it right side up; it simply gets the info and assembles it the right way
- physics review- real image is where rays converge; virtual image is where rays appear to diverge; real images are inverted
- review optics notes you made :)
Duplicity
duplex theory of retina
2 photoreceptors: rods (light/dark) and cones (color)
Cones- fine detail, bright light- 3 types based on wavelength that they best absorb light
S/short= blue; M/medium = green; L/long = red
400 nm, 550 nm, 700 nm
6 million cones
Rods- less detail/low resolution, night vision/low light, single pigment = rhodopsin
120M rods
Cones restricted almost exclusively to fovea (middle of retina)
Macula
- middle of retina
- separates peripheral and central vision (central inside)
- zones
- dark portion inside macula is FOVEA— cones + strongest visual acuity (sharpness of vision)
-You can survive w/o peripheral vision (only reflexes affected); macular degeneration = lose central vision = blind
Peripheral vision
- our peripheral vision isn’t that strong- less accurate/resolute/saturated(color)
- grayscale; but we perceive color b/c we expect objects to not change color
Optic disk
Blind spot
-no photoreceptors
-optic nerve which photoreceptors connect to
photoreceptors - bipolar cells- ganglion cells - optic nerve
-it’s not that your brain is filling in the info; it’s that your brain is just not looking for info there
Light path w/in eye
- not all the light that travels through the lens makes it through retina
- light must go through retina/ganglion cells/bipolar cells to reach photoreceptors
- multiple rods wired to one bipolar cell = low resolution
- cones - 1 cone : 1 bipolar cell- more accurate
Light path eye to brain
- Light from eyes to optic nerve to OPTIC CHIASM (some optic nerve fibers from one eye cross optic nerve fibers from other eye)
- to optic tract to THALAMUS (Lateral geniculate nucleus in thalamus)
- **LGN organizes info based on depth, motion, shape/form, color (“mail room”) through optic tract still
- to occipital lobe/visual cortex
object in right visual field = left retina of both eyes, left LGN, left occipital
An example w/ broccoli bc why not
- Broccoli on right side of head = light rays hit left side of visual field
- Signals from LH side of both visual fields of eye go to left side of brain, to LEFT LGN to left part of occipital lobe
-Optic chiasm is where the nasal visual fields (nerves of inside of each eye/medial) cross path/ decussate
Visual cortex
FEATURE DETECTORS
- in cerebral cortex, in occipital lobe
- back of brain
- visual cortex contains feature detectors
ex) things that respond to lines like divisions of shapes in the world that are oriented horizontally, or vertical - when you sense shapes/outlines- cells in both LGN (reorganize info) and visual cortex fire based on where those contours are
ex) fire when something moves left to right, or R to L - in visual cortex, signals are so well organized that researchers can take signals from visual cortex after projecting image on display & reproduce it on another display = RETINOTOPIC MAP
- if you look at visual cortex & where info is, it corresponds to where info is in environment = you get a pic of what’s going on in cortex in retinotopic map
- from here, signal sent to rest of cerebral cortex, to association areas- reason & respond to it
Summary of pathway eye to brain
Eyes - LGN of thalamus (reorganize/repackage info) - to visual cortex of occipital lobe (a lot of analysis) - to cerebral cortex (thinky stuff goes on)
Processing
- processing in sequences takes too long; do PARALLEL PROCESSING
ex) allows for good hand-eye coordination; fraction-of-second reaction
(in sequence = process colors, then shapes, then motion, etc)
-perception of env would lag behind env
Parallel processing - brain takes info / signal and processes the various parts of it in different places at the same time = FASTER
- Color processed by cones (dif cones respond to different wavelengths of light)
- Shape - in thalamus’s LGN —> its PARVOCELLULAR CELLS (parvo = small)- high color spatial resolution = see fine detail; but low temporal resolution = only w/ immobile/slow-moving objects
- *this is why things appear blurry when moving really quickly
- Motion - magnocellular cells of thalamus (Magno = large) - high temporal resolution- can tell when things are moving, but can’t necessarily distinguish individual shapes (high temporal resolution but low spatial resolution)
-then all info sent to occipital lobe at same time; process there; BOOM you’re done
