Chapter 5 Flashcards by Ms Lucy

type of neuron in the retina that receives input directly from the receptors

bipolar cells

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area at the back of the retina where the optic nerve exits; it is devoid of receptors

blind spot

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the ability to recognize colors despite changes in lighting

color constancy

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inability to perceive color differences

color vision deficiency

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type of retinal receptor that contributes to color perception

cones

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a tiny area of the retina specialized for acute, detailed vision

fovea

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ganglion cells in the fovea of humans and other primates

ganglion cells

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statement that whatever excites a particular nerve always sends the same kind of information to the brain

law of specific nerve energies

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ganglion cells in the fovea of humans and other primates

midget ganglion cells

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result of staring at a colored object for a prolonged length of time and then looking at a white surface, the image is seen as a negative image, with a replacement of red with green, green with red, yellow and blue with each other, and black and white with each other

negative color afterimage

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idea that we perceive color in terms of opposites

opponent-process theory

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ganglion cell axons that exit through the back of the eye and continue to the brain

optic nerve

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chemicals contained in rods and cones that release energy when struck by light

photopigments

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an opening in the center of the iris where light enters

pupil

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the rear surface of the eye, which is lined with visual receptors

retina

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concept that the cortex compares information from various parts of the retina to determine the brightness and color for each area

retinex theory

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type of retinal receptor that detects brightness of light

rods

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theory that color is perceived through the relative rates of response by three kinds of cones, each one maximally sensitive to a different set of wavelengths

richromatic theory (or Young-Helmholtz theory)

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area of the world that an individual can see at any time

visual field

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What happens when you see something?

Light rays reflect off the object and strike your retina

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If you look at a picture, how do the neurons in your brain represent it?

Neither

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What is the law of specific nerve energies?

Each sensory neuron conveys a particular type of sensation, such as light or sound.

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What makes the blind spot of the retina blind?

The optic nerve and blood vessels occupy this space, leaving no room for receptors.

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Vision in the periphery of the retina has poor sensitivity to detail but great sensitivity to faint light. Why?

Toward the periphery, the retina has more convergence of input.

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Input to the human visual cortex comes from cones and rods (by way of ganglion cells) in what proportion?

About 90 percent of input to the cortex comes from cones.

Suppose you perceive something as red. According to the trichromatic theory, what is the explanation?

Light from the object has excited your long-wavelength cones more strongly than your other cones.

If you stare at a white circle surrounded by a green background, and then look at a white surface, you perceive a green circle surrounded by a red background. What does this observation imply about the opponent-process theory?

Opponent-process color perception depends on the visual cortex, not just the cells in the retina.

An object that reflects all wavelengths equally ordinarily appears gray, but it may appear yellow, blue, or any other color, depending on what?

Contrast with surrounding objects

Which theory most readily accounts for the observation described in question 9?

Retinex theory

What evidence shows that color, such as greenness, is in the brain and not in the light itself?

Some people are unable to see certain colors despite otherwise normal vision.

a decreased responsiveness to one kind of line or another, caused by an asymmetric curvature of the eyes

astigmatism

stimulation from both eyes

binocular

the ability to respond in limited ways to visual information without perceiving it consciously

blindsight

type of visual cortex cell located in areas V1 and V2 that responds to a pattern of light in a particular orientation anywhere within its large receptive field

complex cells

visual cortex cells that respond to a bar-shaped pattern of light in a particular orientation, but only if it does not extend beyond a certain point

end-stopped (or hypercomplex) cells

neurons whose responses indicate the presence of a particular feature

feature detectors

type of cell that receives input from receptors and delivers inhibitory input to bipolar cells

horizontal cells

small ganglion cells that occur throughout the retina

koniocellular neurons

thalamic nucleus that receives incoming visual information

lateral geniculate nucleus

the reduction of activity in one neurons by activity in neighboring neurons

lateral inhibition

large cell bodies with large receptive fields that are distributed evenly throughout the retina

magnocellular neurons

small cell bodies with small receptive fields in or near the fovea

parvocellular neurons

area of the cortex responsible for the first stage of visual processing

primary visual cortex (or area V1)

the area in visual space that excites or inhibits any neuron

receptive field

the discrepancy between what the left and right eyes see

retinal disparity

time early in development when experiences have a particularly strong and enduring influence

sensitive period

type of visual cortex cell that has a receptive field with fixed excitatory and inhibitory zones

simple cell

(or strabismic amblyopia or lazy eye) a condition in which the eyes do not point in the same direction

strabismus

What is the order of connections from receptors to visual cortex?

Receptors—bipolar cells—ganglion cells—lateral geniculate—visual cortex

Axons from the nasal half of the retina go to the____hemisphere of the brain. Axons from the temporal half of the retina go to the____hemisphere of the brain.

contralateral … ipsilateral

When light strikes a receptor, the effect is to____ the bipolar cells and____ the horizontal cells. The horizontal cells____ the bipolar cells.

excite excite inhibit

If light strikes one receptor, the net effect is to___the nearest bipolar cell and___other bipolar cells to the side because of the contributions from___cells.

excite inhibit horizontal

Suppose light strikes the retina in a circle, surrounded by dark. Which bipolar cells will show the greatest response, and which will show the least?

Bipolars connected to the receptors just inside the circumference of the circle respond most. Those connected to receptors just outside the circumference respond least.

As we progress from bipolar cells to ganglion cells to later cells in the visual system, what happens to the size of receptive fields?

They become larger.

In contrast to parvocellular neurons, magnocellular neurons are more sensitive to___

movement

If you were in a darkened room and researchers wanted to know whether you were having visual fantasies (without asking you), they could measure activity in which brain area?

The primary visual cortex

What is meant by blindsight?

Some people with damage to the primary visual cortex accurately guess the location or other properties of objects they say they don’t see.

How could a researcher determine whether a given neuron in the visual cortex is simple or complex?

If it responds to a stimulus in just one location, it is a simple cell. If it responds in several locations, it is a complex cell.

What do cells within a column of the visual cortex have in common?

They respond best to lines in the same orientation.

What is the evidence that certain types of feature detectors operate in the human visual cortex?

After you stare at a waterfall or other steadily moving display, you see stationary objects as moving in the opposite direction.

If a kitten has one eye shut for its first few weeks of life, its visual cortex becomes insensitive to that eye. Why?

Activity from the active eye displaces synapses from the inactive eye.

What early experience is necessary to maintain binocular input to the neurons of the visual cortex?

Cortical cells must usually receive simultaneous input from the two eyes.

Why is it important to correct astigmatism early?

The visual cortex becomes more sensitive to the lines it sees best.

If someone is born with dense cataracts on both eyes, and the cataracts are removed years later, which of these aspects of vision remains permanently impaired?

Motion perception and depth perception

visual path in the parietal cortex that helps the motor system locate objects; the “where” path

dorsal stream

brain area of the inferior temporal cortex that recognizes faces

fusiform gyrus

portion of the cortex where neurons are highly sensitive to complex aspects of the shape of visual stimuli within very large receptive fields

inferior temporal cortex

an impaired ability to perceive movement

motion blindness

(medial superior temporal cortex), temporal cortex area that responds best to the expansion, contraction, or rotation of a visual display

MST

area of the brain that detects moving objects

MT (or area V5)

the inability to recognize faces due to damage of several brain areas

prosopagnosia

voluntary eye movements

saccade

area of the brain that processes information from the primary visual cortex and transmits it to additional areas

secondary visual cortex

visual paths in the temporal cortex that are specialized for identifying and recognizing objects; the “what” path

ventral stream

an inability to recognize objects despite otherwise satisfactory vision

visual agnosia

Within the visual system of the brain, the ventral stream is more important forand the dorsal stream is more important for___

identifying objects … controlling movements

Visual agnosia usually results from damage to which part of the cortex?

Temporal cortex

What impairment is typical after damage to the fusiform gyrus?

Difficulty recognizing faces

Which part of the visual cortex is most important for color vision, especially color constancy?

Area V4

Why is it difficult to watch your own eyes move when looking in the mirror?

During saccadic eye movements, activity decreases in area MT.

What happens after damage limited to area MT? What may occur if MT is intact but area V1 is damaged?

Damage to MT causes motion blindness. If MT is intact but V1 is damaged, the person perceives movement but cannot identify the object.