Vision Flashcards Preview

Biological and Cognitive Foundations > Vision > Flashcards

Flashcards in Vision Deck (50):

sensory transduction

stimuli impinge on receptors and alter membrane potentials


receptor potentials

a slow, graded electrical potential produced by a receptor cell in response to physical stimulus 

the electrical changes in the membrane potential. don't have axons. effect the release of neurotransmitters and modify firing in neurons. correlated with strength of the stimulus. 


What is light determined by?

hue: the wavelength of light. we detect a range of hues on the visible spectrum (color)
saturation: purity of light. full saturation is when the radiation is one wavelength 
brightness: intensity of light. high intensity = more brightness


How does light come into the eye?

the amount of light coming through the pupil is regulated by the iris
light enters through the pupil 
lens focuses the light onto the retina. when you want to bring something to focus, the lens flattens


ciliary muscles

contract the lens in order to look at distant and near objects (accomodation)



eyes move so one point is projected to corresponding areas on both retinas


macular degeneration

visual distortion (damage to retina), come and go vision, better night vision (rod cells unaffected), peripheral vision sensitivity 




less prevalent, but provide us with the most information because they are used in daytime
provide us with acuity (sharpness) and color vision



center of retina



retinal region for acute vision
only contains cones
contains an equal amount of ganglion and cones compared to the peripheral retina



more prevalent than cones
sensitive to light
help us to see at night
color blind & lack foveal vision in dim light 


optic disk

collection of axons leaving the eye to the optic nerve
where the blind spot is located
no photoreceptors


retina and corresponding layers

3 layers 
bipolar cell
ganglion cell
(horizontal and amacrine cells: combine messages from photoreceptors for lateral communication)


bipolar cell

2 arms that connect to shallowest and deepest layers of the retina


ganglion cell

axons travel to optic nerve to bring information to the rest of the brain
in the periphery of the retina, neurons are more likely to activate the ganglion cell, but will mean the receptive field is not very precise 


horizontal cell

neuron in the retina transmitting information to outer processes of bipolar cells


amacrine cells

neuron in retina that transmits information to inner processes of bipolar cells



responsible for transduction, which is the first step in visual perception
special molecules in the membrane of the lamallae contain opsin (protein) and retinal (lipid)



the outer layer of a photoreceptor containing photopigments 


How does visual information travel from the optic nerve to the brain?

after travelling through the optic nerve, the information reaches the dorsal lateral geniculate nucleus, which has 6 layers
magnocellular (2) large cell bodies
parvocellular (4) small cell bodies
koniocellular ventral to magno and parvo layers
the lateral geniculate nucleus sends axon information through optic radiations to the primary visual cortex in the calcarine fissure located in medial and posterior occipital lobe


How does hyperpolarization happen in vision?

when light strikes a molecule of photopigment in a photoreceptor, the retinal molecule detaches from the opsin- causing a hyperpolarization of the membrane.  then the rate of firing of the ganglion cell changes, signaling detection of light 


an opsin molecule is exposed to light, it bleaches the photopigment and splits it to produce a receptor potential
the photoreceptor releases less neurotransmitter 


how does depolarization happen in vision?

because the neurotransmitter normally hyperpolarizes the membrane of the bipolar cell, the reduction causes a depolarization
this depolarization causes the bipolar cell to release more neurotransmitter, which excites teh ganglion cell


receptive field

portion of visual field in which the presentation of visual stimuli will produce and alteration in the firing rate of a particular neuron

(part of visual field that an individual neuron "sees")


optic chiasm

where optic nerves join together at the base of the brain. the ganglion cell axons on the inner half of the retina cross through chiasm and to the lateral geniculate nucleus on opposite side of the brain. axons from the outer halves remain on the same side of the brain. 

image of world on retina is inverted 

A image thumb

primary visual cortex

often called the striate cortex (V1)
nerve fibers carry information from V1 to extrastriate areas (V2, V3, V4, V5)

Blindsight-Damage to V1: some patients have ability to respond to visual stimuli while reporting "not seeing" 


periphery of retina

because many receptors only converge on a single ganglion cell (compared to the fovea), it brings information from a large area of the retina and the peripheral vison is not very precise.


types of ganglion cells

ON cells-increase rate of firing
OFF cells- signal decreases in firing
ON/OFF cells- respond when light goes on and again when light goes off


center surround organization

enhances our ability to detect outlines of objects even when the contrast between the object and the background is low

our visual system adds the borders


color mixing

the addition of two or more light sources
trichromatic theory
opponent colors theory

mixing blue,red, and green paint= gray

mixing blue, red and green light= white 


What types of cones are responsible for color vision and how much creates each color?

the opsin absorbes different wavelength of light

blue cone (419nm)
green cone (531 nm)
red cone (559 nm)

rod (496 nm)



Explain color coding in the retina

red light turns on red cone, which excites red/green ganglion=>RED
green light turns on green cone, which inhibits red/green ganglion=>GREEN
yellow light turns on red and green cones, red cone excites red/green and blue/yellow ganglion, green cone inhibits red/green ganglion=>CANCELLATION OF RED/GREEN; blue cone excites blue/yellow ganglion=>YELLOW
blue light turns on blue cone, which inhibits the blue/yellow ganglion=>BLUE

A image thumb

 negative afterimage

caused by adaptation in rate of firing of retinal ganglion cells. when ganglion cells are excited or inhibited for a prolonged period, they later show a rebound effect and fire faster or slower than normal


simple cells

(Hubel & Wiesel)

orientation neurons that are organized in opposition. A line may excite if placed at the center, but inhibit the cell if moved away. 


complex cell

(Hubel & Wiesel)

a cell that continues to respond while the line was moved within the receptive field. movement detectors respond to white on black and black on white


hypercomplex cell

(Hubel & Wiesel)

detects the location of ends of lines at particular orientation


How do color ganglion transmit information?

the information is transmitted through parvo and koniocellular laters of lateral geniculate nucleus to cells in the cytochrome oxidase blobs


V1 of visual cortex

first layer with cytochrome oxidase blobs
neurons respond to orientation, movement, spatial frequency, retinal disparity, and color


V2 of visual cortex

2nd layer with three stripes (thick, thin, and pale)


ocular dominace

the extent to which a particular neuron receives more input from one eye than from the other


ventral stream

bottom stream

begins with neurons in pale and thin V2 stripes, continues to V4, then projects to inferior temporal cortex

involved with perception of objects 



dorsal stream


begins with neurons in thick V2 stripes and ascends to posterior parietal cortex
"where" "how" 

perception of movement, location, visual attention, control of eye and hand movements



color constancy

colors of objects stay the same even when the environment is dull, artificial, or bright
this is regulated by V4


cerebral achromatopsia

vision without color
cannot remember the colors they saw before damage to V8


fusiform face area

visual association cortex
involved in perception of faces and other complex objects that require expertise to recognize


extrastriate body area

activated by photos and silhouettes
perception of human body and body parts other than the face


parahippocampal place area

activated by scenes and backgrounds


types of visual agnosias (4 kinds)

apperceptive-can't perceive objects visually (Mrs R at beginning of chapter- couldn't identify watch unless she touched it); can't copy 
associative-can't identify objects that are perceived visually; disconnect btw perceptions and verbal systems; can copy
prosopagnosia-can't recognize particular people by seeing their faces
object-can't recognize objects



inability to perceive movement 
caused by damage to V5


What is involved in the perception of movement?

visual information arrives sooner in V5 than it does in V4. 
V5 contains neurons that respond to movement
the medial superior temporal cortext (adjacent to V5) contains neurons that respond to complex patterns of movement


sensory receptors

a specialized neuron that detects a particular category of physical events (don't confuse with receptors for NT's/hormones)