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