Chapter 3: Visual system: The Eye Flashcards
Photon
A single particle of light
Electromagnetic energy
A form of energy that includes light that is simultaneously both a wave and a particle
Wavelength
The distance between two adjacent peaks in a repeating wave; different forms of electromagnetic energy are classified by their wavelengths
Intensity
When referring to waves, the height of a wave
Frequency
The number of waves per unit of time; frequency is the inverse of wavelength
Sclera
The outside surface of the eye; a protective membrane covering the eye that gives the eye its characteristic white appearance
Anterior chamber
The fluid-filled space between the cornea and the iris
Iris
The colored part of the eye; a muscle that controls the amount of light entering the pupil
Pupil
An opening in the middle of the iris
Pupillary reflex
An automatic process by which the iris contracts or relaxes in response to the amount of light entering the eye; the reflex controls the size of the pupil
Heterochromia
A condition in which a person has irises of two different colors
Posterior chamber
The space between the iris and the lens; it is filled with fluid known as aqueous humor
Lens
The adjustable focusing element of the eye, located right behind the iris; also called the crystalline lens
Accommodation
The process of adjusting the lens of the eye so that both near and far objects can be seen clearly
Ciliary muscles
The small muscles that change the curvature of the lens, allowing accommodation
Zonule fibers
Fibers that connect the lens to the choroid membrane
Near point
The closes distance at which an eye can focus
Presbyopia
A condition in which incoming light focuses behind the retina, leading to difficulty focusing on close -up objects; common in older adults, in whom the lens becomes less elastic
Retina
The paper-thin layer of cells at the back of the eye where transduction takes place
Retinal image
The light projected onto the retina
Rods
Photoreceptors at the periphery of the retina; they are very light sensitive and specialized for night vision
Cones
Photoreceptors in the fovea of the retina; they are responsible for color vision and our high visual acuity
Fovea
An area on the retina that is dense in cones but lacks rods; when we look directly at an object, it’s image falls on the fovea
Macula
The center of the retina; the macula includes the fovea but is larger than it
Optic disc
The part of the retina where the optic nerve leaves the eye and heads to the brain; along the optic disc, there are no receptor cells
Photopigment
A molecule that absorbed light and by doing so releases an electric potential
Opsin
the protein portion of a photopigment that captures the photon of light and begins the process of transduction; the variation in opsin determines the type of visual receptor
Retinal
A derivative of vitamin A that is part of a photopigment
Hyperpolarization
a change in the voltage of a neuron whereby the inside of the cell becomes more negative than it is in its resting state
Neurotransmitter
a chemical substance neural cells release to communicate with other neural cells
Duplex theory of vision
the doctrine that there are functionally two distinct ways in which our eyes work, the photopic, associated with the cones, and the scotopic, associated with the rods
Photopic vision
the vision associated with the cones; it is used in the daytime, has good acuity in the fovea, and has color vision
Scotopic vision
the operation of the visual system associated with the rods; it has relatively poor acuity and no color ability but is very sensitive to light
Purkinje Shift
the observation that short wavelengths tend to be relatively brighter than long wavelengths in scotopic vision versus photopic vision
Convergence
the number of photoreceptors that connect to each ganglion cell; more convergence occurs for rods than for cones
Dark adaptation
the process in the visual system whereby its sensitivity to low light levels is increased
Light adaptation
the process whereby the visual system’s sensitivity is reduced so that it can operate in higher light levels
Receptive field
a region of adjacent receptors that will alter the firing rate of a cell that is higher up in the sensory system; the term can also apply to the region of space in the world to which a particular neuron responds
Edge detection
the process of distinguishing where one object ends and the next begins, making edges as clear as possible
Center-surround receptive field:
a receptive field in which the center of the receptive field responds opposite to how the surround of the receptive field responds; if the center responds with an increase of activity to light in its area, the surround responds with a decrease in activity to light in its area
On-center receptive fields
retinal ganglion cells that increase their firing rate (excitation) when light is presented in the middle of the receptive field and decrease their firing rate (inhibition) when light is presented in the outside or surround of the receptive field
Off-center receptive fields
retinal ganglion cells that decrease their firing rate (inhibition) when light is presented in the middle of the receptive field and increase their firing rate (excitation) when light is presented in the outside or surround of the receptive field
Lateral inhibition
the reduction of a response of the eye to light stimulating one receptor by stimulation of nearby receptors, caused by inhibitory signals in horizontal cells
Myopia
a condition causing an inability to focus clearly on far objects, also called nearsightedness; occurs because accommodation cannot make the lens thin enough
Hyperopia
a condition causing an inability to focus on near objects, also called farsightedness; occurs because accommodation cannot make the lens thick enough
Field of view
The part of the world you can see without eye movements
Astigmatism
a condition that develops from an irregular shape of the cornea or the lens, which makes it impossible for the lens to accommodate a fully focused image
Cataracts
a condition that results from a darkening of the lens
Macular degeneration:
a disease that destroys the fovea and the area around it
Retinitis pigmentosa
an inherited progressive degenerative disease of the retina that may lead to blindness
Tapetum
a reflective layer behind the receptors of nocturnal animals that bounces light not caught by receptors back into the retina
Compound eye
an eye that does not have a single entrance but is made up of many separate components called ommatidia
How is visible light measured?
by the wavelength, and frequency of the electromagnetic energy.
An example of an animal with a wide field of view and an animal with a narrow field of view. What are the advantages and disadvantages of each?
An animal that has a wide field of view is that of the pronghorn antelope that has its eyes on the sides of its head. The advantage that the antelope has is that it has a wider field of view that it makes it possible for it to see the front and back of its head. The disadvantage is that it has a limited depth perception.
An animal that has a narrow field of view is the owl. The narrow field of view is what increases the depth perception, which helps it easier to target prey and has less distractions that come from having a peripheral vision. However, the disadvantage is that it is has a low sense of awareness of its surroundings, making them vulnerable.
Where are cones the most dense?
in the fovea of the retina
Why is the location of the optic disc associated with the blind spot?
The optic disc is the spot where the optic nerve connects to your eye. There are no light detecting cells there so that what makes that part of your vision a blind spot. You don’t notice it because your brain fills in the missing details.
spatial summation
it refers to our eyes ability to pool light in different area, depending on the amount of light the cones and rods are receiving. For example, when it is darker or nighttime, eyes will absorb more light to see better but things will be blurrier.
The tough membrane that protects the eye is known as the white, or ______.
sclera
Visible light is an example of ______ energy.
electromagnetic
The Purkinje shift is the transition from dim to bright light. T/F
False
Which of the following is most likely to be true of an animal that has eyes at the front of its head?
It hunts for its food
Vision associated with cones is known as _________ vision.
photopic
The purpose of the retina is to ______ light.
capture
Which of the following has the greatest effect on how bright a light appears?
number of photons
What causes astigmatism?
an irregularly shaped cornea or lens
What is a wavelength?
the distance between two peaks in a repeating wave
What is one way that a cat eye differs from a human eye?
A cat eye lacks a fovea
