vision Flashcards
retina
most visual processing
receptive surface inside the eye
contains photoreceptor
captures light and front & projects detailed images of external world onto a layer of neurons
transduction
conversion of 1 form of energy to another
light to neural signals
cornea
transparent outer layer of eye
forms image on the retina
focus light
refraction
bending of light rays by change in density of medium
eye glasses
telescopes
microscopes
lens
focus an image on the retina
changes shape to fine tune image
ciliary muscles
control shape of lens inside the eye
focuses image on retina
accommodation
ciliary muscles adjust lens to bring nearby objects into focus
myopia
nearsightedness
difficulty seeing distant objects
develops if eyeball is too long
extraocular muscles
control movement of eyes
photoreceptors
respond to light
rods and cones adjust to light sensitivity
rods
focused in periphery of retina
low levels of light
convergence = sensitivity to weak stimuli
less acuity `
Cones
focused in center of retina (fovea)
good w colors
no convergence = less sensitivity
better acuity
photopigments
special receptor molectules in rods and cones that capture light
rhodspin
photopigment in rods
ganglion cells
class of cells in retina whose axons form optic nerve
optic nerve (cranial nerve II)
collection of ganglion cell axons that extend from retina to brain
scotopic system
in retina
operates at low levels of light
involves rods
very sensitive
convergence
phenomenon of neural connections
photopic system
system in retina
operates at high levels of light
involves cones
Photoreceptors are hyper polarized in…
light
less neurotransmitter released
photoreceptors are depolarized in …
dark
more neurotransmitter released
pupil
opening formed by iris
allows light to enter eye
pupil contraction
closing
parasympathetic division of autonomic nervous system
dilation of pupil
opening
sympathetic region “fight or flight”
iris
circular structure of eye
provides opening to form the pupil
surrounds pupil
range fractionation
sensory systems cover wide range of intensity values
each sensory receptor cell specializes in 1 part of overall range intensities
photoreceptor adaptation
tendency of rods and cones to adjust their light sensitivity to match current levels of illumination
visual acuity
sharpness of vision
fovea
central portion of retina
packed w/ highest density of photoreceptors
center of our gaze
high density of cones
optic disc
region of retina without photoreceptors
blind spot
portion of visual field from which light falls on optic disc
optic chiasm
point at which parts of 2 optic nerves cross midline and project to opposite hemispheres
optic tract
axons of retinal ganglion cells after they’ve passed optic chiasm
Lateral geniculate Nucleus (LGN)
where most axons terminate
part of thalamus that receives info from optic tract
sends info to visual areas in occipital cortex
optic radiations
axons of LGN that terminate in primary visual areas of occipital cortex
primary visual cortex
region of occipital cortex where most visual info first arrives
topographic projection
mapping that preserves point-to-point correspondence btw neighboring parts of space
order of processing in retina
photoreceptors —> bipolar cells —> ganglion cells —> optic nerve
receptive field
stimulus features that inhibit or excite cells
every level of vision has receptive field
on center bipolar cells
inhibited by glutamate
in light —>Special skills activated depolarized –> more neurotransmitter released
in dark —> hyper polarized —> less neurotransmitter released
off-center bipolar cells
excited by glutamate
in dark –>depolarized –> increased –> neurotransmitter release
in light –> special skills activated —> hyper polarized —> decreased neurotransmitter released
on center ganglion cells
conditions w/ light —> increased firing rates
condition w/o light —> decreased firing rates
activated when light is presented to center
off center ganglion cells
conditions w/ light —> decreased firing rates
conditions w/o light –> increased firing rates
activated when light is presented to periphery of cells receptive field
on center / off surround
stimulation of center excites cell of interest, stimulation of surround inhibits
off-center / on-surround
stimulation of center inhibits cell of interest, stimulation of surround excites
simple cortical cells
cell in visual Cortex
responds to edge / bar with a particular width, orientation, and location in visual field
complex cortical cells
cell in visual Cortex
needs movement to make it respond actively
on-center receptive fields
light hits cone —> hyper polarized —> decreased neurotransmitter release
off-center receptive fields
dark —> photoreceptors depolarized –> more neurotransmitter released
