Chapter 5 - Quiz 2 Flashcards
The Eye and its connections to the brain: route within the retina
Where do messages go from the eye to the retina? (2)
-receptors at the back of eye to bipolar cells, then ganglion cells
-additional cells called amacrine cells get info from bipolar cels and send it to other bipolar, amacrine and ganglioln cells
-in the fovea, a single bipolar cell attaches to a single ganglion cell
The Eye and its connections to the brain: route within the retina
What is the optic nerve made of?
-ganglion cells axons join to form it
-your brain fills in the gap of the blind spot and your other eye can see what the blind spot of the one eye cannot
The eye and its connections to the brain: fovea and periphery
What is the midget ganglion cells?
-the ganglion cells in humans and primates
-each is small and responds to just a single cone
-each cone in the fovea has a direct route to the brain
-birds have two fovea
Visual Receptors: Rods and Cones
What are rods functional for and where are they primarily located? (2)
-periphery
-not useful in daylight because bright light bleaches them
-rods outnumber cones but cones provide about 90% of the brain’s input
Visual Receptors: Rods and Cones
Where are cones primarily located and what are their functions? (2)
-fovea
-less active in dim light, more useful in bright light and essential for color vision
Color vision: the trichromatic (Young-Helmholtz) theory
What is the trichromatic theory/Young-Helmholtz theory?
-we perceive color through the relative rates of response by three different cones
-incomplete as a theory of colour vision
-each cone is sensitive to a different set of wavelengths (short is blue, medium is green yellow and long is orange red)
Color: The trichromatic theory
What is a visual field?
-everything you can see in both fovea and peripheral vision with moving the head
Color vision: the opponent-process theory
What is the opponent process theory? What is an example? (2)
-we percieve color in terms of opposites, brain perceives color on a continuum and after you stare at one color long enough you swing to the opposite
-for example, a bipolar cell receives excitation from short-wavelength cone and inhibiition from long and medium wavelength cone, after prolonged exposure the fatigued cell decreases its response and because a low level of response by that cell usually means yellow, you percieve yellow
-negative color afterimage (when you stare at something and look away and continue to see light within that shape)
-continuum includes red to green, yellow to blue and white to black
Color Vision: Stop and check Pg 156
According to the trichoromatic theory, why do we see red?
-A perception of red occurs only if the long-wavelength cone has a high ratio of response relative to the other two types of cone.
-cpmparison is the key
-Activity of the long-wavelength cone is not sufficient.
-the long-wavelength cone responds to what we call yellow more than to what we call red.
Color vision: stop and check Pg 156
According to the opponent process theory, under what circumstances would you perceive a white object as blue?
-If you stared at a bright yellow object for a minute or so and then looked at a white object, it would appear blue.
Color vision: The Retinex Theory
What is color constancy? Which theories cannot explain it very well? (2)
-the ability to recognize colors despite changes in lighting
-trichoromatic theory and the oppnent-process theory
Color vision: The Retinex theory
What is the retinex theory?
-the cortex compares information from various parts of the retina to determine brightness and color for each area
-examples include looking at two grey blocks that look like different shades of grey but when you put a finger in front of the border, they are actually the same color
-another example is when an object is under yellow vs. blue light. We can still perceive the correct color of a banana even if its under different lights
Color vision: Stop and Check Pg 157
When a television set is off, its screen appears gray. When you watch a program, parts of the screen appear black, even though more light is actually showing on the screen than when the set was off. What accounts for the black perception?
-The black experience arises by contrast with the brighter areas around it.
Color vision: stop and check Pg 157
Figure 5.9 shows light at about 510 nm as green. Why should we nevertheless not call it “green light”?
-Color perception depends not just on the wavelength of light from a given spot but also the light from surrounding areas.
Color vision: color vision deficiency
What is color vision deficiency and what is it caused by? (2)
-people with certain genes fail to develop one type of cone or develop an abnormal cone
-colorblindness
General Principles of Perception
What is the law of specific nerve energies?
-the nature of a sensation is determined by the specific type of sensory nerve that is stimulated, rather than the stimulus itself
-each type of sensory nerve is associated with a particular type of sensation
-the brain codes information largely in terms of which neurons are active and how active they are at any moment. Impulses in certain neurons indicate light, whereas impulses in others indicate sound, touch or other sensations.
Visual Receptors 5.1: Summary
People who vary in their number of axons from the retina to the brain, specifically people who have more axons show a greater ability to what?
-detect brief, faint or rapidly changing stimuli
5.1 Visual Receptors: End of Chapter Quiz
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.
-the afterimage effect requires higher level processing beyond the initial response of retinal cells
5.2 An overview of the mammalian vsual systemi
What is the sequence of synaptic connections in the retina starting from the rods and cones? (3)
-Rods and cones synapse with horizontal and bipolar cells.
-Horizontal cells inhibit bipolar cells.
-Bipolar cells then synapse with amacrine and ganglion cells, all within the eyeball.
An overview of mammalian visual system
Information for the nasal half of each eye and the temporal half of each eye cross to what side of the brain? (2)
-nasal half crosses to the contralateral hemisphere (otherside)
-temporal half crosses to the ipsilateral hemisphere (same side)
An overview of the mammalian visual system
Where do most ganglion cells axons go to?
-this is also essentially asking where does the optic nerve go
-what part of the brain?
-lateral geniculate nucleus
-part of thalamus
-some cells go to hypothalamus and superior colliculus
-looks somewhat like a knee
-sends zons to other parts of the thalamus and the visual cortex
Processing in the retina
What is the purpose of lateral inhibition and how does it work? (2)
-sharpens contrast and borders
-receptors send messages to excite nearby bipolar cells and also sends messages to horizontal cells that slightly inhibit those bipolar cells and the neighbors to their sides. The next result is to heighten the contrast between an illuminated area and its darker surround
Processing in the retina: Stop and Check Pg 164
When light strikes a receptor, does the receptor excite or inhibit the bipolar cells? What effect does it have on horizontal cells? What effect does the horizontal cell have on bipolar cells? (2)
-The receptor excites both the bipolar cells and the horizontal cell.
-The horizontal cell inhibits the same bipolar cell that was excited plus additional bipolar cells in the surround
Processing in the retina: Stop and Check Pg 164
If light strikes only one receptor, what is the net effect (excitatory or inhibitory) on the nearest bipolar cell that is directly connected to that receptor? What is the effect on bipolar cells to the sides? What causes that effect? (2)
-It produces more excitation than inhibition for the nearest bipolar cell.
-For surrounding bipolar cells, it produces only inhibition. The reason is that the receptor excites a horizontal cell, which inhibits all bipolar cells in the area.
5.2 Further Processing
What is a receptive field?
-the area in visual space that excites or inhibits a cell in the visual system
-each cell has one
-the receptive field of a rod or cone is simply the point in space from which light strikes the cell
-other visual cells derive their receptive fields from the connections they receive
-if light from a particular spot excites the neuron, then that location is part of the neuron’s excitatory receptive field. If it inhibits activity, the location is in the inhibitory receptive field.
Further Processing
Explain the three types of ganglion cells in primates: parvocellular, magnocellular and koniocellular (3)
-parvocellular neurons: small cell bodies and small receptive fields are mostly in or near fovea. respond to color and detailed shape
-magnocellular neurons: large cell bodies and receptive fields are distributed evenly through retina. do not respond to color and respond to movement and broad outlines of shape.
-koniocellular neurons: small cell bodies but theyt occur throughout the retina. Some respond to color and respond to varied stimuli
Further processing: Stop and Check Pg 166
.As we progress from bipolar cells to ganglion cells to later cells in the visual system, are receptive fields ordinarily larger, smaller, or the same size? Why
-They become larger because each cell’s receptive field is made by inputs converging at an earlier level.
The Primary Visual Cortex
Information from the lateral geniculate nucleus of the thalamus usually goes to where?
-primary visual cortex in the occipital cortex
-AKA as Area V1 or striate cortex
The primar visual cortex
What happens if someone damages the primary visual cortex?
-they will report having no conscious vision, no visual imagery and no visual images in dreams
-can show blindsight
The Primary Visual Cortex
What is blindsight?
-when people with damage to the primary visual cortex can respond to visual stimuli without consciously perceiving them
-could navigate around obstacles, detec movement or identify objects in the visual field
-indicates that some visual processing occurs outside of conscious awareness
The Primary Visual Cortex
What does research around blindsight suggest? (2)
-small islands of healthy tissue remain in a damaged visual cortex that can support some visual functions
-the thalamus sends visual input to several other brain areas, including part of the temporal cortex
The Primary Visual Cortex: Simple and Complex receptive fields
What is a simple cell? What shapes or movements does it respond best to? (2)
-a cell with a receptive field with a fixed excitatory and inhibitory zone
-bar-shaped and horizontal/vertical
-only in V1 area
The primary Visual Cortex: Simple and Complex cells
What does a complex cell respond to?
-pattern of light in particular orientation anywhere within its large receptive field
-in V1 and V2 area
-a cell that responds to stimulus in only one location is a simple cell, one that responds equally throughout a large area is a complex cell
The primary visual cortex: Simple and complex cells
What does an end-stopped or hyper complex cell respond to?
-resemble complex cell except?
-has strong inhibitory area at one end of its bar-shaped receptive field
-the cell responds to a bar-shaped pattern of light anywhere in its broad receptive field, provided the bar does not extend beyond a certain point
The Primary Visual Cortex: The columnar organization
What do cells with similar properties in the visual cortex do?
-they group together in columns
-cells grouped together have the same orientation preference
Primary Visual Cortex: are visual cortex cells feature detectors?
What is a feature detector
-neurons whose response indicate the presence of a particular feature
Development of the visual cortex: deprived experience in both eyes
What is a sensitive period?
-when experiences have a particularly strong and enduring influence
Development of the visual cortex: deprived experience in one eye
What happens if a young animal can see in one eye but not the other?
-synapses in the visual cortex gradually become unresponsive to input from the deprived eye and after a while, even if the eye works again the animal will not be able to see with it
Development of the visual cortex: deprived experience in both eyes
What happens if both eyes of a kitten were sutured closed?
-if neither eye is active, no axon outcompetes another. For a while, the visual cortex remains responsive to visual input
Development of the visual cortex: uncorrelated stimulation in the two ey
What is retinal disparity?
-the discrepancy between what the left and right eyes see
-stereoscopic depth perception requires this
-by comparing the inputs from two eyes, you achieve stereoscopic depth perception
Development of visual cortex: uncorrelated stimulation in two eyes
What woud happen if a kitten had damaged eye muscles so that its eyes do not point in the same direction?
-cortical neurons do not consistently receive messages from one eye that match messages from the other, results in poor depth perception
-experience fine-tunes binocular vision
Development of visual cortex: uncorrelated stimulation in two eyes
What is strabismus?
-lazy eye
-solution sometimes is to wear a patch over the active eye
Development of visual cortex: early exposure to a limited array of patte
What causes astigmatism?
-assymetric curvature of the eyes
5.3 Ventral and Dorsal Paths
Where does the V1 area send information to?
-secondary visual cortex
-processes the info furter and transmits it to additional areas
-anterior to V1 in the occipital cortex
The ventral and dorsal pathway
What is the ventral stream? (2)
-through temporal cortex is known as perception pathway
-because of its importance for identifying and recognizing objects
-or what pathway
-damage to this area causes an inability to name the object, recognize faces etc but someone can still pick up objects appropriately and move them
The ventral and dorsal paths
What is the dorsal stream through and why? (2)
-through parietal cortex and is action pathway or how pathway
-because of its importance for visually guided movements
-damage to this area causes people to be able to recognize objects but not accurately move out to touch them or move between them
Detailed analysis of shape: Recognizing faces Stop and Check Pg 181
The brain has no specialized areas for perceiving flowers, clothes, or food. For what items does it have specialized areas?
-The temporal cortex has specialized areas for perceiving places, faces, and bodies, including bodies in motion
Detailed analysis of shape: Recognizing faces Stop and Check Pg 181
The ability to recognize faces correlates with the strength of connections between which brain areas?
-Ability to recognize faces correlates with the strength of connections between the occipital face area and the fusiform gyrus.
Motion Perception: The Middle Temporal Cortex
What are the two areas espcially important for motion perception?
-MT (middle temporal cortex)
-MST ( medial superior temporal cortex
-receive input mostly from the magnocellular path
-MT is color insensitive
Motion Perception: The Middle Temporal Cortex
What do most cells in area MT respond to?
-They respond selectively to movement at a particular speed and direction, detect acceleration or deceleration, and respond to motion in all three dimensions.
Motion Perception: The Middle Temporal Cortex
What type of stimuli do cells in the dorsal part of area MST respond best to?
-They respond best to complex stimuli like the expansion, contraction, or rotation of a large visual scene, as experienced when moving forward, backward, or tilting your head.
Motion Perception: Motion Blindness
When you move your eyes, why does it not seem as if the world is moving?
-Neurons in areas MT and MST respond strongly when an object moves relative to the background, and not when the object and background move in the same direction and speed.
