Chapter 4 Terms, Summary & Review Questions Flashcards
Accommodation of the Lens
adjustment of the thickness of the lens to focus on objects at different distances
Blind Spot
retinal area where the optic nerve exits
Brightness Contrast
increase or decrease in an objects apparent brightness by comparison to objects around it
Color Constancy
tendency of an object to appear nearly the same color under a variety of lighting conditions
Cone
visual receptors adapted for color vision, daytime vision, and detailed vision
Cornea
rigid, transparent structure on the surface of the eyeball
Dark Adaptation
gradual improvement in the ability to see in dim light
Electromagnetic Spectrum
continuum of all the frequencies of radiated energy
Fovea
central area of the human retina
Ganglion Cells
neurons in the eye that receive input from bipolar cells, which in turn receive input from the visual receptors
Iris
colored structure on the surface of the eye surrounding the pupil
Lens
flexible structure that varies its thickness to adjust its focus on objects at different distances
Negative Afterimage
perception of new colors after the removal of other ones
Opponent-Process Theory
theory that we perceive color in terms of a system of paired opposites: red versus green, yellow versus blue, and white versus black
Optic Nerve
set of ganglion cell axons that turn around and exit the eye
Perception
interpretation of sensory information
Pupil
adjustable opening in the eye
Receptor
specialized cell that converts environmental energies into signals for the nervous system
Retina
layer of visual receptors covering the back surface of the eyeball
Retinex Theory
concept that the cerebral cortex compares the patterns of light coming from different parts of the retina and synthesizes a color perception for each area
Rod
visual receptors that are adapted for vision in dim light
Sensation
conversion of energy from the environment into a pattern of response by the nervous system
Stimulus
energy from the world that affects us in some way
Trichromatic Theory (or Young-Helmholtz theory)
theory that color vision depends on the relative rate of response of three types of cones
You may have heard people say that cats can see in total darkness. Is that possible?
A- Yes, they send rays out of their eyes that enable them to see in the dark.
B- Yes, they see in the dark, although no one knows how they do it.
C- Dont be ridiculous. Vision is the detection of light, so vision in darkness is impossible.
C- Dont be ridiculous. Vision is the detection of light, so vision in darkness is impossible.
Why do we have our most detailed vision from the part of the retina called the fovea?
A- The fovea has the greatest density of receptors.
B- The lens and cornea focus light most clearly on the fovea.
C- The fovea is the point most distant from the blind spot.
D- The fovea has an equal ratio of cones and rods.
A- The fovea has the greatest density of receptors.
Why do we detect faint light more effectively in the periphery of the retina than in the fovea?
A- The periphery has more tightly packed receptors.
B- The center of the retina is in the shadow of the pupil.
C-The periphery of the retina has more cones, which are more sensitive to faint light.
D- In the periphery, more receptors converge their output onto the next cell
D- In the periphery, more receptors converge their output onto the next cell
After light stimulates receptors at the back of your retina, where do the receptors send their output?
A- Directly to the thalamus
B- Directly to the cerebral cortex
C- To other neurons that are closer to the center of the eye
C- To other neurons that are closer to the center of the eye
What fills the blind spot of the retina?
A- The lens
B- The fovea
C- A bone
D- Axons and blood vessels
D- Axons and blood vessels
According to the trichromatic theory, how does our nervous system tell the difference between bright yellow-green and dim yellow-green light?
A- By the relative rates of response by medium-wavelength and long-wavelength cones
B-By the relative rates of response by medium-wavelength and short-wavelength cones
C-By the relative rates of response by all three types of cones
D- By the total amount of activity by all three types of cones
D- By the total amount of activity by all three types of cones
Which of these phenomena does the opponent-process theory explain better than the trichromatic theory does?
A- The tendency of an objects apparent color to change depending on variations in the objects surrounding it
B-The fact that color vision is better in the fovea than in the periphery
C- Negative color afterimages
D- The fact that people can mix three colors of light to match any other color
C- Negative color afterimages
Which of these phenomena does the retinex theory explain better than the trichromatic theory or the opponent-process theory does?
A- The tendency of an objects apparent color to change depending on variations in the objects surrounding it
B-The fact that color vision is better in the fovea than in the periphery
C-Negative color afterimages
D-The fact that people can mix three colors of light to match any other color
A- The tendency of an objects apparent color to change depending on variations in the objects surrounding it
How vision works.
Vision occurs when light rays strike the retina at the back of the eye, causing cells to send messages to the brain. We do not send sight rays out of the eyes.
Light
Light is the part of the electromagnetic spectrum that excites receptors in the eyes. If we had different types of receptors, we would define other wavelengths as light.
Focus
The cornea and lens focus light onto the retina.
Cones and Tods.
Cones, found mainly in and near the fovea, are essential for color vision. Rods, more numerous toward the periphery, detect dim light.
Blind spot.
The blind spot is the area of the retina through which the optic nerve exits.
Color vision.
Color vision depends on three types of cones, each sensitive to a particular range of light wavelengths. Cones transmit messages so that later cells in the visual system indicate one color (e.g., blue) by an increase in activity and another color (e.g., yellow) by a decrease. The cerebral cortex compares responses from different parts of the retina to determine color experiences.
Color vision deficiency.
Complete color-blindness is rare. Certain people have difficulty distinguishing reds from greens for genetic reasons.
