Chapter 5: Notes Flashcards
What are four types of messages that are sent to the brain to interpret as experiences?
Color, sound, taste, smell
Law of Specific Nerve Energies
Activity by a particular nerve always conveys the same type of information to the brain.
*Example: Impulses from one neuron indicate light, impulses from another neuron indicate smell
Where is your perception?
In the brain; you see when light alters brain activity or feel when touch information reaches the brain.
Where in the eye does light enter?
Pupil; the center of the iris
Where is light focused in the eye?
Focused by the lens and cornea onto the retina (rear surface of the eye), which is lined with visual perceptors
What is the contralateral arrangement in the eye?
Light from the left side of the world falling on the right side of the eye and vice versa
Light from above falling to the bottom of the eye and vice versa
Where are Bipolar cells located and what is their function?
Closer to the center of the eye; receive messages from receptors at the back of the eye
Where are Ganglion cells located and what is their function?
Closer to the center of the eye than the bipolar cells; receive messages from bipolar cells
What are amacrine cells?
Additional cells that get information from bipolar cells and send it to other bipolar, ganglion, and amacrine cells.
What is the optic nerve made out of?
Consists of ganglion axon cells; exits through back of the eye
What is a blind spot?
A place with no receptors, such as in the optic nerve and where blood vessels enter the eye
Why don’t we notice blindspots?
The other eye compensates
What is the fovea?
Tiny area specialized for acute, detailed vision
What is the fovea’s line of connection?
Fovea->bipolar cell->ganglion cell->axon to the brain
Connects almost directly to a cone
What are midget ganglion cells?
Ganglion cells in humans and primates
What happens when an eye lens becomes stiff?
Far-sight or near-sight
What is the order of information passing through the retina?
Rods/Cones in retina->bipolar cells->ganglia cells->axons which form optic nerve
How do cells in the eye allow light to enter?
They are transparent
What happens toward the periphery of the retina?
More and more receptors converge into bipolar and ganglion cells
What does the periphery retina do?
It allows for greater perception in the dark, though it has less detail
Do cones or rods detect color?
Cones detect color, rods do not
What kind of receptors do vertebrate retina consist of?
Rods and cones
Rods
Most abundant in the periphery and respond to faint light (120 million per retina)
Cones
Concerned with color and therefore light (16 million per retina)
*Though outnumbered by rods, provides 90% of the brain’s input
Photopigments
Chemicals in both rods and cones that release energy when struck by light
Transduction
Process by which physical energy is transformed into nerve impulses
What are photopigments made out of?
11-cis-retinal, which is bound to proteins called opsins, that light quickly turns into all-trans-retinal
What is the perception of color dependent on?
The wavelength of light; visible light is only a small portion of the electromagnetic spectrum.
Trichromatic (Young-Helmholtz) Theory
We perceive color by comparing responses across a few types of receptors, each of which is sensitive to a different range of wavelengths.
Young-Helmholtz Theory
We perceive color through the relative rates of response by three kinds of cones, each kind maximally sensitive to a different kind of wavelength: short, medium, and long wavelength
How do we discriminate the three wavelengths in the Young-Helmholtz Theory?
The radio of activity across the three types of cones
What colors do each of the three cones in the Young-Helmholtz Theory perceive?
Short: Blue/violet
Medium: Green
Long: Red
How are the three cones in the Young-Helmholtz Theory distributed? In turn, what colors do we see?
The three cones are unevenly distributed with more medium/long cones being present than short ones, meaning we see red and green more easily than blue.
Opponent-Process Theory
Suggests that we perceive color in terms of pairs of opposites; the brain has a mechanism that perceives color on a continuum.
-One from red to green, another from blue to yellow
What is one possible mechanism for Opponent-Process Theory?
Bipolar cells are excited by one set of wavelengths and inhibited by another.
What evidence both supports the Opponent-Process Theory and claims the Trichromatic Theory is incomplete?
Negative color afterimages
What do afterimages depend on?
Likely depends on the cerebral cortex rather than ganglion or bipolar cells
Retinex Theory
Suggests the cortex compares info from various parts of the retina to determine the brightness and color for each area.
What does the Trichromatic theory and Opponent-Process Theory not easily explain?
Color constancy
Color constancy
The ability to recognize colors despite changes of lighting
Brightness constancy
You perceive differences when there are none; perception of the brightness of an object requires comparing it with other objects
What is color deficiency? (Also known as “color blindness”)
A person who lacks one or two (very rarely three) types of cones. The most common type of color deficiency is red/green.
*The opposite is the addition of a fourth cone, found in women, allowing them to see red differently
What causes color deficiency? (Also known as “color blindness”)
It’s a genetic condition found in the X chromosome
*8% in men, 1% in women
Optic chasm
Place where 2 optic nerves leaving the eye meet
Which side does visual information that hits the eyes stay?
Visual information that hits the eye stays on that side
*Example: something that hits the left side, inner will stay in the inner
Where do most ganglion axon cells go?
Lateral geniculate nucleus
Lateral inhibition
The reduction of activity in one neuron by activity in neighboring neurons
What is the main function of lateral inhibition?
It sharpens contrast to emphasize the border of objects
How do receptors get a heightened contrast between an illuminated area and its darker surroundings?
Receptors in the retina send messages to excite nearby bipolar cells and also send messages to inhibit horizontal cells that slightly inhibit those bipolar cells and neighbors to their sides
How is lateral inhibition important for functions in the nervous system?
Olfaction: A strong stimulus can suppress the response to another one that follows slightly after it due to inhibition of the olfactory bulb
Touch: Stimulation of one spot on the skin weakens response to stimulation of a neighboring spot
Hearing: Inhibition makes it possible to understand speech amongst irrelevant noise
Receptive field
Part of the receptive field that excites or inhibits it
*Each cell in the visual system has a receptive field
What is the receptive field of a receptor?
The point in space in which light strikes the cell
How do other cells derive their receptive fields?
Through patterns of excitatory and inhibitory connections
What are the three types of ganglion cells in primates?
Parvocellular—highly sensitive to color and visual details
Magnocellular—highly sensitive to overall pattern and moving stimuli
Koniocellular—have several functions and their axons terminate in many different places
Where are the three types of ganglion cells in primates?
Parvocellular—In or near fovea; small cell bodies
Magnocellular—Distributed evenly throughout fovea; larger cell bodies and receptive fields
Koniocellular—Occur throughout the retina; small cell bodies
What are the implications of having so many different kinds of ganglion cells?
The brain doesn’t have to do everything and they can process information immediately
Primary visual cortex
Area V1 or striate cortex; located in the occipital cortex
What does V1 do?
Receives information from the lateral geniculate nucleus and is the area responsible for the first stage of visual processing
Aphantasia
People who can’t see or hear in their minds
Hyperphantasia
People who have an intense ability to see or hear in their minds
Blindsight
An ability in people with damage to Area V1—they respond to visual information that they report not seeing. The person is not consciously aware of this
What is one explanation for blindsight?
Small islands of healthy tissue may survive in an otherwise damaged area.
What are three types of cells in the visual cortex?
Simple, complex, and end-stopped/hypercomplex
Simple cell (visual cortex)
Has a receptive field with fixed excitatory and inhibitory zones; most have bar-shaped or edge-shaped receptive fields
Complex cell (visual cortex)
Located in Areas V1 and V2—doesn’t respond to the exact location of an object; responds to a pattern of light in a particular orientation (such as a vertical bar) anywhere in its large receptive field
End-stopped/hypercomplex cell (visual cortex)
Resembles complex cell but has a strong inhibitory area at one end of its bar-shaped receptive field
How are cells grouped in the visual cortex?
Cells having various properties are grouped in the visual cortex in columns perpendicular to the surface. Cells respond to either the left eye, right eye, or both eyes equally.
What do neurons in the Area V1 respond to?
Bar or edge-shaped patterns; activity in these cells may be necessary for the perception of a bar, line, or edge
Feature detector
Neuron that indicates the presence of a particular feature
What happens when feature detectors are given prolonged exposure to a specific visual feature?
It decreases sensitivity to those features in the neuron.
*Creates the waterfall illusion
What causes the waterfall illusion?
Staring at a moving stimulus for a prolonged time (such as a waterfall) fatigues/saturates the cells in your eyes detecting them and inhibiting the opposite. Looking away causes the fatigued cells to shut down and the inhibited ones to fire, causing the world to move in a way opposite of what you just stared (up if at a waterfall)
Why do we see optical illusions?
Due to feedback from other cortical areas to changes in responses in your primary visual cortex
Your brain’s response to any visual stimulus depends on your expectations as well as the stimulus itself
When do the normal properties of the visual system of mammals develop?
Before birth
What happens if an eyelid is shut in cats or primates for the first 4-6 weeks of their life?
Synapses in their visual cortex gradually become unresponsive to input from deprived eye
What happens if both eyes of a kitten remain shut for the first few weeks of life?
Cortical responses become sluggish and lose well-defined receptive fields.
Sensitive period
When experiences have a particularly strong and enduring influence
Stereoscopic Depth
A method of perceiving distance in which the brain compares slightly different input from two eyes
*Relies on the discrepancies between the left and right eyes
How do cortical neurons shape their ability to detect retinal disparity?
The ability of cortical neurons to adjust their connections to detect retinal disparity is shaped through experience
Strabismus
“Lazy Eye”; Eyes don’t point in the same direction and give two different messages to the brain
What happens if a kitten is fitted with goggles painted with horizontal stripes?
This leads to nearly all of the visual cortex cells becoming responsive to only that pattern.
Astigmatism
Refers to a blurring of vision for lines in 1 direction caused by asymmetric curvature of the eyes
*70% of infants have astigmatism
Secondary Visual Cortex
Area V2; receives information from the primary visual cortex, processes it further, and transmits it to additional areas
Ventral stream
The “what” pathway; connection of visual paths in the temporal cortex
*Damage results in people being unable to describe what they can see
Dorsal stream
The “where” pathway; helps the motor system locate objects
*Damage results in people knowing what things are but not knowing where they are (don’t integrate vision with arm and leg movements)
In Area V2, what do cells respond best to?
Many respond best to lines, edges, and sine wave gratings, but some respond to circles, perpendicular lines, and other complex patterns
Where do the receptive properties of cells become more complex?
Further on in the visual processing system
What do cells in the Inferior Temporal Cortex learn to respond to?
Meaningful objects, the sight of an object from different viewpoints
Visual Agnosia
Inability to recognize objects despite otherwise satisfactory vision. Most common is facial recognition
What causes visual agnosia?
Damage to the pattern pathway usually in the temporal cortex; ventral stream damage
When does facial recognition develop?
Soon after birth; children show strong preference to a right-side-up face
Prosopagnosia
Severe problem in recognizing faces; people may not recognize their own children. Though they will recognize voices.
*Damage to the fusiform gyrus of the inferior temporal cortex
Super-recognizer
Can easily recognize people they’ve seen once or twice. Have a richer than average connection between the fusiform gyrus and occipital cortex.
Motion perception
Involves a variety of brain areas in all 4 lobes of the cerebral cortex
What areas of the brain are especially activated by motion?
Area MT (Area V5) and MST (Medial Superior Temporal Cortex)
What types of movement do the cells in Area MT respond to?
Respond selectively to objects that move in a particular direction, at a particular speed, detect acceleration or deceleration, and respond to implied movement in photos.
What do the cells in Area MST respond best to?
Complex stimuli like expansion, contraction, or rotation of a large visual scene
What is the difference in response in Area MT and the ventral part of MST between something moving relative to the background and something moving in the same direction and speed as the background?
They respond more briskly to the former than the latter; MT and MST neurons enable people to distinguish between the result of eye movement and result of object movement
Motion Blindness
Able to see objects but impaired at seeing whether they are moving or, if so, which direction and how fast
Likely caused by damage in Area MT
Saccades
Decrease in the activity of the visual cortex during quick eye movements. Neural activity and blood blow decrease 75 milliseconds before activity and during, causing motion blindness
Why do saccades exist?
Part of several mechanisms that prevent confusion or blurring of images during eye movements
