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Visual System PSY 250
Terms in this set (74)
Human vision can see which part of the electromagnetic spectrum?
380-760 nm of wavelength
Visual stimuli are inherently _______and human perception is ______.
extent of visual space seen by each eye
the ability to detect light
the ability to distinguish between two nearby points in space
begins when visual receptors convert light energy into neural signals
Advantage of having one eye to each side of the head?
see almost 360 degrees; wider visual field
Advantage of having both eyes in front?
the difference in the position of the same image on the two retinas help the brain create 3D/depth perception
where light enters eye
regulates amount of light entering eye
What does Iris' function depend on?
level of illumination
change shape to focus visual images on the retina
accomodation of lens?
process of lens change
where light rays are converted into neural signals by photoreceptors
Two unique spots of retina?
FOVEA and BLIND SPOT
center of macula
no photoreceptors, axons of cells go through to form optic nerve + blood vessels (to provide nutrients)
Photoreceptors have a role in _____ and _____ of visual stimuli.
Two types of photoreceptors
Cones and rods
PHOTOPIC & color vision; predominant in bright lighting; high acuity: provide both color and detail
SCOTOPIC & black and white vision, predominant in dim lighting; high sensitivity, but lack of color and detail
Low convergence in cone-fed circuits
High convergence in rod-fed circuits
Light ____ Rhodopsin
Rhodopsin regain _____ ability in the dark
Rhodopsin molecules are bleached which causes rods to _______,_________ glutamate release.
Concepts about Seeing
-sometimes we see MORE
-sometimes we see LESS
-need to resolve ambiguities in visual world
-perception is subjective
Blind Spot demo
-seeing is more than what your eyes can capture
-seeing is also less than what your eyes can capture
How can we have clear and detailed vision?
1) fovea allows high acuity vision
2) brain does some tricks (perceptual conception-cannot see blind spot)
3) eye movements (saccades)-put object of interest on fovea
Visual acuity depends on...
1) convergence ratio
3) density of receptors
high acuity--> low convergence ratio, centralized distribution, high density of receptors
area of blindness caused by damage of Visual Cortex
way to map the "blind" visual areas
explains why people don't notice deterioration of their vision
-mediated by secondary visual pathways e.g. superior colliculi
-explains why we can still "see" pretty well despite most cones are found in fovea
sum of inputs received during last few fixations
what happens when images are stabilized retina?
image will fade
photoreceptors are _____sensors
abstraction of visual scene because visual system makes good "guesses" through history of experiences
lens of eye projects into retina...
focused, inverted, and reversed image
LGN Lateral geniculate nucleus
in visual thalamus--> main subcortical nuclei that carries visual signal to the cortex; it has 6 layers of cells, receives ~90% of retinal input, input from each eye remain separated in each LGN
Primary Visual Cortex
buried deep in posterior region of occipital around Calcarine fissure, also has 6 layers, LGN projects to layer 4 of V1
-V1 is first stage of visual processing in cerebral cortex
Visual cortex and LGN are ______organized
organization like a map of retina
Disproportionate cortical representation of the fovea
higher concentration of receptors in a retinal area--> larger cortical representation
Activity pattern of visual neurons determine ____of stimulus in space and ______
location, what it is
Neural activity is ______to the strength of light intensity
Neurons in the retinal-geniculate-striate pathway all have _______.
The receptive field of retinal ganglion cell is the _______that when stimulated with light, changes the cell's activity
area of retina (visual space)
Receptive field comes in diff forms:
2 areas of recpetive field
center and surround
if light is simultaneously shown on "on area" and "off area"
weak or no effect
Most retinal ganglion cells have concentric center-surround receptive fields
LGN have same properties as retinal ganglion cells
Neurons in V1 respond best to
bars of light (not responsive to spots of light)
2 major classes of v1 neurons:
1) simple cells (monocular-respond to light from only one eye)
2) complex cells
only respond ot lines/bars of specific orientation
has clear "on" and "off" areas
their RFs are larger than simple cells
many are binocular -respond to both eyes
mechanism in visual system that enhances perception of brightness contrast between two areas
neural basis of edge detection
enhancing effect of a cell behavior by inhibiting neighboring cells
"winner take all"
sharpens SPATIAL RESOLUTION (aids 2 point discrimination)
How does lateral inhibition work?
more intense light striking--> higher firing rate
-when receptor fires, inhibits neighboring receptors
--stronger light intensity has greater inhibition on neighboring neurons
trichromatic theory, 3 kinds of cones: RGB
Opponent process theory
occurs at all levels of visual system beyond receptors
-red vs green, blue vs. yellow; b/w
observation of color CONSTANCY and color CONTRAST
-perception of color is determined by reflectance in a context
--same spectra can generate different color percepts
--different spectra can generate the same color precept
directing behavioral interaction with objects
responsible for conscious recognition of objects
ventral extrastriate damages
hard time differentiating two objects
difficulty preparing for action
failure to recognize visual image
inability to recognize faces though not so straightforward
concentration of mental effort on sensory or mental events
improve perception of target or interest and can interfere with other items in the scene
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