PSYC 3300 Study Guide - Final Guide: Visual Acuity, Ganglion Cell, Receptive Field
Vision
• Anatomy of the eye, internal and external
o External
• Iris: colored part of the eye that controls pupil dilation and constriction
• Pupil: opening of the eye where light is allowed to enter
• Cornea: transparent outer layer that refracts light
• Lens: flexible tissue that inverts images and has the muscular control of focus
o Inner
• The retina: light sensitive structure at the rear of the eye that consists of light
sensitive receptor cells called photoreceptors
• Blindspot: the optic nerve that exits the eye at the optic disk which creates a
blindspot because there are no photoreceptors
• Fovea (pit): specialized for detailed visual acuity
▪ Blood vessels are absent
▪ Tightly packed cone receptor cells
▪ Each cone receptor is connected to one bipolar cell and one ganglion cell
• Photoreceptor types and locations
o Photoreceptors are located in the very back of the eye
o Light that reaches the photoreceptors activates nearby cells
o The nearby cells send info to neurons throughout the visual stream that are close
together
o Bipolar cells and ganglion cells are connected to the photoreceptors
• Neural signals are sent from the photoreceptor to the bipolar cells and bipolar
cells send information to ganglion cells
• Axons of ganglion cells form the optic nerve
o Rods
• Greater number: 120 million
• Less information to the brain
• Numerous in the periphery
• Less convergenge/acuity
• Photopigment- rhodopsin
• More sensitive to light
• One type
• No color vision
o Cones
• Smaller number: 6 million
• Provide 90% of the input to brain
• Less sensitive to light
• Function better in bright light compared to dark and dim light
• Concentrated in and around the Fovea
▪ 1:1 ratio of cones to ganglion cells
• More visual acuity
• Smaller receptive fields
• Photopigment: lodopsin
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• 3 Types:
▪ Red, green, blue or L,M,S
▪ L and M are far more abundant than S
▪ It's easier to see red, yellow, and green than blue
• Ganglion cell types
o Info from photoreceptors -> bipolar cells -> ganglion cells
o axons of ganglion cells form the optic nerve which creates a blindspot because
there are no photoreceptors
o Three types: parvocellular, magnocellular, and koniocellular (extra credit answer)
• Parvocellular: small receptive fields, in cones, color sensitive, carry detailed
visual info
• Magnocellular: large cell bodies and receptive fields, in periphery, in rods, not
color sensitive, respond to movement broad outlines
• Receptive fields
o The area of the retina where one ganglion cell receives input from
o High convergence = large receptive field = less visual acuity
o Cones have low convergence = small receptive fields
o Rods have high convergence = large receptive fields
o Ganglion cell receptive fields are made up of receptors arranged in circles
• Typically a round center surrounded by a larger circle
• The receptive field might be excited by light in the center or light in the
surround
o On center: light in the center excites ganglion cell and light in surround inhibits
o Off center: light in the surround excites the ganglion cell and light in center inhibits
o Early receptive fields and lateral inhibition is effective for light/dark contrast and
edge detection
• Theories of color vision
o Young-Helmholtz Trichromatic Theory
• We perceive color by processing the response rates of the three types of cones
and each is more sensitive to a specific wavelength
• Red, green, blue are the primary colors
• People can match any color by mixing the three different wavelengths
(short=blue, medium=green, long=red)
• The primary colors cannot be broken down into other components
• Colors stay constant but the brightness and intensity can change
• Weakness:
▪ Cannot explain color aftereffects ( why we see certain colors after looking
at other colors for extended durations
▪ Cannot explain color blindness
• Contributions:
▪ Combination of three sources of input is enough to perceive any
wavelength of visible light
▪ Predicted three photopigments in cone cells
o The Opponent Process Theory
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
Vision: anatomy of the eye, internal and external, external. Iris: colored part of the eye that controls pupil dilation and constriction: pupil: opening of the eye where light is allowed to enter, cornea: transparent outer layer that refracts light. Lens: flexible tissue that inverts images and has the muscular control of focus. Less information to the brain: numerous in the periphery. Less convergenge/acuity: photopigment- rhodopsin, more sensitive to light, one type, no color vision, cones. L and m are far more abundant than s. It"s easier to see red, yellow, and green than blue: ganglion cell types. Inability to process object-specific qualities damage to inferior temporal cortex: all info from these streams are sent to the prefrontal cortex, damage to pathways can lead to distinct types of visual agnosia. Movement: muscle types, smooth muscle: contracts the internal organs, peristalsis, vasoconstriction, bladder function, cardiac muscle: heart muscle.
