Ch6-Vision Flashcards
information is stored in terms of responses by neurons based on….
- which neurons respond
- their amount of response
- timing of their responses
whatever excites a particular nerve establishes a special kind of energy unique to that nerve
law of specific nerve energies (influences what we perceive)
Every stimulation of the optic nerve is perceived as light. This statement is an example of….
law of specific nerve energies
center of the iris, where light enters
pupil
rear surface of the eye, lined with receptors
retina
located closer to center of the eye, receive messages from receptors at back of the eye (retina)
bipolar cells
located still closer to center of eye, receive messages from bipolar cells
ganglion cells
additional cells that get info from bipolar cells & send it to other bipolar cells, other amacrine cells, and ganglion cells
amacrine cells
consists of ganglion cell axons, exits through the back of the eye and travels to brain
optic nerve
has no receptors, where optic nerve leaves the back of the eye
blind spot
why do we not notice our blind spot?
compensation between eyes
in the retina, messages go from the back of the eye to _____
bipolar cells, then to ganglion cells, then exits through the optic nerve
tiny area specialized for acute, detailed vision [packed tight with receptors]
fovea
each receptor in ____ connects to a single bipolar cell, which in turn connects to a single ganglion cell, which has an axon to the brain
fovea
ganglion cells in fovea of humans and primates
midget ganglion cells
less detailed vision, allows for greater perception of much fainter light
peripheral vision
abundant in periphery of retina, respond to faint light, not useful in bright light
rods (useful for night vision)
abundant in & near fovea, less active in dim light, more useful in bright light, & essential for color vision
cones (useful for color vision)
ratio of rods to cones in humans
cones are 1/20 as abundant as rods
cones provide 90% of brains input
number of axons in optic nerve
average is 1 million
some have 2 to 3 times more; ex) tennis players show faster brain response to stimuli
chemicals in both rods & cones that release energy when struck by light
photo-pigments
we perceive color through relative rates of response by 3 kinds of cones, each kind maximally sensitive to a different set of wavelengths [short, medium, and long wavelengths]
Trichromatic (Young-Helmholtz) Theory
perceive color in terms of opposites-the brain has a mechanism that perceives color on a continuum
Red to Green
Yellow to Blue
White to Black
Opponent-Process Theory
afterimages occur due to ____
rebound effect from wavelengths being saturation while some are inhibited
cortex compares info from various parts of the retina to determine the brightness & color for each area [includes color constancy]
Retinex Theory
ability to recognize colors despite changes in lighting
color constancy
perceive differences in brightness when there are none - perception of brightness of an object requires comparing it with other objects
brightness constancy
some people lack 1 or 2 of the 3 types of cones; some people have 2 kinds of cones, but 1 is abnormal
color vision deficiency
[red-green most common]
optic nerves from the 2 eyes meet at the _____
optic chiasm
most ganglion axons go to the optic nerve then the optic chiasm then the _____ [part of the thalamus]; special for visual perception, sends to thalamus & occipital cortex
lateral geniculate nucleus
reduction of activity in one neuron by activity in neighboring neurons; heightens contrast to emphasize borders of objects
lateral inhibition
part of the visual field that excites or inhibits it [what excites the cell in the outside world]; point in space from which light strikes the cell
receptive field
3 categories of ganglion cells in primates
parvocellular neurons
magnocellular neurons
koniocellular neurons
small cell bodies & small receptive fields - located mostly in or near fovea [highly sensitive to color & visual detail]
parvocellular neurons
larger cell bodies & receptive fields & are distributed evenly throughout retina [highly sensitive to overall patterns & moving stimuli]
magnocellular neurons
small cell bodies, but occur throughout the retina [have several functions & axons terminate in many different places]
koniocellular neurons
cortical area where conscious visual perception occurs
V1
responsible for first stage of visual processing; located in occipital cortex
primary visual cortex = V1 = striate cortex
people with damage to area V1; people respond to visual info that they report not seeing
blindsight
Hubel & Wiesel recorded from cells in brains of cats & monkeys and distinguished which types of cells in visual cortex?
simple, complex, & end-stopped (hypercomplex) cells
has receptive field with fixed excitatory & inhibitory zones; most have bar-shaped or edge-shaped receptive fields
simple cells
responds to pattern of light in a particular orientation anywhere within its large receptive field [sensitive to diagonal bars, esp. when moving]; located in v1 & v2, does not respond to exact location of stimuli
complex cells
resembles complex cell, but has a strong inhibitory area at one end of its bar-shaped receptive field [responds provided the object does not cross a certain point in the visual field]
end-stopped (hypercomplex) cells
neuron that indicates the presence of a particular feature [prolonged exposure to a given visual feature decreases sensitivity to that feature]
feature detector
most neurons in visual cortex receive ______; input from both eyes
binocular input
if each eye is alternately covered during the first few weeks of life, would the visual cortex still receive binocular input
no, most cortical neurons would respond to stimuli in each eye separately, not at the same time
what happens if both eyes are kept shut for the first few weeks of life?
synapses are inhibited
time period when experiences have particularly strong & enduring influence
sensitive period
comparison of slightly different inputs from both eyes allows you to achieve _______
stereoscopic depth perception
stereoscopic depth perception requires the brain to detect _______; the discrepancy between what the left & right eyes see
retinal disparity
eyes do not point in same direction, both eyes are active, but no cortical neuron consistently receives messages from one eye that match the other eye
strabismus (lazy eye)
about 70% of infants have _______, blurring of vision for lines in one direction [caused by asymmetric curvature of eye]
astigmatism
if we compare receptive fields of two simple cells in primary visual cortex, how are they most likely to differ?
orientation of line that they respond to
receives info from primary visual cortex (v1), processes it further, & transmits it to additional areas
secondary visual cortex (V2)
visual pathway in parietal cortex; the “where” pathway - helps motor system locate objects [find objects & move towards them
dorsal stream
what is damaged if people can tell what things are but not where they are
dorsal stream
collection of visual paths in temporal cortex; the “what” pathway - identifying & recognizing objects
ventral stream
what is damaged if people cannot describe what they are seeing
ventral stream
as visual info goes from simple cells to complex cells to other brain areas, the receptive fields become more _____
specialized
cells in _____ respond to identifiable objects; respond to what viewer perceived, not physical stimulus
inferior temporal cortex
inability to recognize objects despite otherwise satisfactory vision, results from damage in temporal cortex
visual agnosia
area that responds strongly to faces, much more than anything else [located in inferior temporal cortex]
fusiform gyrus
inability to recognize faces, can distinguish gender & age but not recognize individual; occurs from damage to fusiform gyrus
prosopagnosia
people with motion blindness have probably suffered damage to the
middle-temporal cortex [area v5]
able to see objects but impaired at seeing whether they are moving or, if so, which direction & how fast
motion blindness
decrease activity during voluntary eye movements
saccades
some people are blind except for ability to detect which direction something is moving, which area is this due to
middle-temporal cortex and lateral geniculate nucleus
