Chapter 3

Question 1

What is a wavelength?

Answer 1

For light energy, the distance between one peak of a light wave and the next peak.

Question 2

What is Visible light?

Answer 2

The band of electromagnetic energy that activates the visual system and that, therefore, can be perceived. For humans, visible light has wavelengths between 400 and 700 nanometers.

Question 3

What are the eyes?

Answer 3

The eyeball and its contents, which include focusing elements, the retina, receptors for vision, and supporting structures.

Question 4

What is the pupil?

Answer 4

The opening through which light reflected from objects in the environment enters the eye.

Question 5

What is the cornea?

Answer 5

The transparent focusing element of the eye that is the first structure through which light passes as it enters the eye. The cornea is the eye’s major focusing element.

Question 6

What is the lens?

Answer 6

The transparent focusing element of the eye through which light passes after passing through the cornea and the aqueous humor. The lens’s change in shape to focus at different distances is called accommodation.

Question 7

What is the retina?

Answer 7

A complex network of cells that covers the inside back of the eye. These cells include the receptors, which generate an electrical signal in response to light, as well as the horizontal, bipolar, amacrine, and ganglion cells.

Question 8

What are the photoreceptors?

Answer 8

The receptors for vision.

Question 9

What are the rods?

Answer 9

A cylinder-shaped receptor in the retina that is responsible for vision at low levels of illumination.

Question 10

What are cones?

Answer 10

Cone-shaped receptors in the retina that are primarily responsible for vision in high levels of illumination and for color vision and detail vision.

Question 11

What are outer segments?

Answer 11

Part of the rod and cone visual receptors that contains the light-sensitive visual pigment molecules.

Question 12

What are visual pigments?

Answer 12

A light-sensitive molecule contained in the rod and cone outer segments. The reaction of this molecule to light results in the generation of an electrical response in the receptors.

Question 13

What is the optic nerve?

Answer 13

Bundle of nerve fibers that carry impulses from the retina to the lateral geniculate nucleus and other structures. Each optic nerve contains about 1 million ganglion cell fibers. (3)

Question 14

What is the fovea?

Answer 14

A small area in the human retina that contains only cone receptors. The fovea is located on the line of sight, so that when a person looks at an object, the center of its image falls on the fovea.

Question 15

What is the peripheral retina?

Answer 15

The area of retina outside the fovea.

Question 16

Are rods and cones in the same place?

Answer 16

The rod and cone receptors not only have different shapes, they are also distributed differently across the retina.

Question 17

What is a condition called macular degeneration?

Answer 17

A clinical condition that causes degeneration of the macula, an area of the retina that includes the fovea and a small surrounding area.

Question 18

What is a condition called retinitis pigmentosa?

Answer 18

A retinal disease that causes a gradual loss of vision, beginning in the peripheral retina.

Question 19

What is the blind spot?

Answer 19

The small area where the optic nerve leaves the back of the eye. There are no visual receptors in this area, so small images falling directly on the blind spot cannot be seen.

Question 20

What is the ciliary muscles?

Answer 20

can change its shape to adjust the eye’s focus for objects located at different distances. This change in shape is achieved by the action of ciliary muscles, which increase the focusing power of the lens

Question 21

What is accommodation?

Answer 21

In vision, bringing objects located at different distances into focus by changing the shape of the lens.

Question 22

What are refractive errors?

Answer 22

Errors that can affect the ability of the cornea and/or lens to focus incoming light onto the retina.

Question 23

What is presbyopia (type of refractive error)?

Answer 23

The inability of the eye to accommodate due to a hardening of the lens and a weakening of the ciliary muscles. It occurs as people get older.

Ex. see objects, or read, at close range

Question 24

What is myopia , or nearsightedness (refractive error)?

Answer 24

An inability to see distant objects clearly. Also called nearsightedness.

Question 25

What can myopia , or nearsightedness be caused by?

Answer 25

1)
refractive myopia , in which the cornea and/or the lens bends the light too much, or

(2)
axial myopia , in which the eyeball is too long.

Question 26

What is hyperopia , or farsightedness?

Answer 26

A condition causing poor vision in which people can see objects that are far away but do not see near objects clearly. Also called farsightedness.

Question 27

What is Transduction?

Answer 27

transformation of one form of energy into another form of energy

Question 28

What is isomerization?

Answer 28

Change in shape of the retinal part of the visual pigment molecule that occurs when the molecule absorbs a quantum of light. Isomerization triggers the enzyme cascade that results in transduction from light energy to electrical energy in the retinal receptors.

Question 29

What is dark adaptation?

Answer 29

Visual adaptation that occurs in the dark, during which the sensitivity to light increases. This increase in sensitivity is associated with regeneration of the rod and cone visual pigments.

Question 30

What is the dark adaptation curve?

Answer 30

The function that traces the time course of the increase in visual sensitivity that occurs during dark adaptation.

Question 31

What is light-adapted sensitivity?

Answer 31

The sensitivity of the eye when in the light-adapted state. Usually taken as the starting point for the dark adaptation curve because it is the sensitivity of the eye just before the lights are turned off.

Question 32

What is dark-adapted sensitivity?

Answer 32

The sensitivity of the eye after it has completely adapted to the dark.

Question 33

What is the defect rod monochromats?

Answer 33

A person who has a retina in which the only functioning receptors are rods.

Question 34

What is rod–cone break?

Answer 34

The point on the dark adaptation curve at which vision shifts from cone vision to rod vision.

Question 35

What is visual pigment bleaching?

Answer 35

The change in the color of a visual pigment that occurs when visual pigment molecules are isomerized by exposure to light.

Question 36

What is visual pigment regeneration?

Answer 36

Occurs after the visual pigment’s two components—opsin and retinal—have become separated due to the action of light. Regeneration, which occurs in the dark, involves a rejoining of these two components to reform the visual pigment molecule. This process depends on enzymes located in the pigment epithelium.

Question 37

What is two important connections between perception and physiology?

Answer 37

1. Our sensitivity to light depends on the concentration of a chemical—the visual pigment.
2. The speed at which our sensitivity increases in the dark depends on a chemical reaction—the regeneration of the visual pigment.

Question 38

What is the condition detached retina?

Answer 38

A condition in which the retina is detached from the back of the eye.

Question 39

What is spectral sensitivity?

Answer 39

The sensitivity of visual receptors to different parts of the visible spectrum.

Question 40

What is spectral sensitivity curve?

Answer 40

The function relating a subject’s sensitivity to light to the wavelength of the light. The spectral sensitivity curves for rod and cone vision indicate that the rods and cones are maximally sensitive at 500 nm and 560 nm, respectively

Question 41

What is monochromatic light?

Answer 41

Light that contains only a single wavelength.

Question 42

What is cone spectral sensitivity?

Answer 42

A plot of visual sensitivity versus wavelength for cone vision. Often measured by presenting a small spot of light to the fovea, which contains only cones. Can also be measured when the eye is light adapted, so cones are the most sensitive receptors.

Question 43

What is the rod spectral sensitivity curve?

Answer 43

The curve plotting visual sensitivity versus wavelength for rod vision. This function is typically measured when the eye is dark adapted by a test light presented to the peripheral retina.

Question 44

What is Purkinje (Pur-kin’-jee) shift?

Answer 44

The shift from cone spectral sensitivity to rod spectral sensitivity that takes place during dark adaptation

Question 45

What is the absorption spectrum?

Answer 45

A plot of the amount of light absorbed by a visual pigment versus the wavelength of light.

Question 46

What are neural circuits?

Answer 46

A number of neurons that are connected by synapses.

Question 47

What are bipolar cells?

Answer 47

A retinal neuron that receives inputs from the visual receptors and sends signals to the retinal ganglion cells

Question 48

What are ganglion cells?

Answer 48

A neuron in the retina that receives inputs from bipolar and amacrine cells. The axons of the ganglion cells are the nerve fibers that travel out of the eye in the optic nerve.

Question 49

What are horizontal cells?

Answer 49

A neuron that transmits signals laterally across the retina. Horizontal cells synapse with receptors and bipolar cells.

Question 50

What are amacrine cells?

Answer 50

A neuron that transmits signals laterally in the retina. Amacrine cells synapse with bipolar cells and ganglion cells.

Question 51

What is Neural convergence?

Answer 51

occurs when a number of neurons synapse onto a single neuron.

Question 52

Do cones have better visual acuity?

Answer 52

Yes (ability to resolve small details)

Question 53

What is the receptive field?

Answer 53

A neuron’s receptive field is the area on the receptor surface (the retina for vision; the skin for touch) that, when stimulated, affects the firing of that neuron.

Question 54

What are center-surround receptive fields in ganglion cells?

Answer 54

A receptive field that has a center-surround organization.

Question 55

What are excitatory and inhibitory areas?

Answer 55

Excitatory: Area of a receptive field that is associated with excitation. Stimulation of this area causes an increase in the rate of nerve firing.

Inhibitory: Area of a receptive field that is associated with inhibition. Stimulation of this area causes a decrease in the rate of nerve firing.

Question 56

What is an excitatory-center, inhibitory-surround receptive field?

Answer 56

A center-surround receptive field in which stimulation of the center area causes an excitatory response and stimulation of the surround causes an inhibitory response.

Question 57

What is an inhibitory-center, excitatory-surround receptive field?

Answer 57

A center-surround receptive field in which stimulation of the center causes an inhibitory response and stimulation of the surround causes an excitatory response.

Question 58

What is center-surround antagonism?

Answer 58

The competition between the center and surround regions of a center-surround receptive field, caused by the fact that one is excitatory and the other is inhibitory. Stimulating center and surround areas simultaneously decreases responding of the neuron, compared to stimulating the excitatory area alone.

Question 59

What is lateral inhibition?

Answer 59

Inhibition that is transmitted laterally across a nerve circuit. In the retina, lateral inhibition is transmitted by the horizontal and amacrine cells.

Question 60

What is the ommatidia?

Answer 60

A structure in the eye of the Limulus that contains a small lens, located directly over a visual receptor. The Limulus eye is made up of hundreds of these ommatidia. The Limulus eye has been used for research on lateral inhibition because its receptors are large enough so that stimulation can be applied to individual receptors.

Question 61

What is edge enhancement?

Answer 61

An increase in perceived contrast at borders between regions of the visual field.

In other words, they help to make edges look more distinct so that we can see them more easily.

Question 62

What is the Chevreul illusion?

Answer 62

Occurs when areas of different lightness are positioned adjacent to one another to create a border. The illusion is the perception of a light band on the light side of the border and a dark band on the dark side of the border, even though these bands do not exist in the intensity distribution

Question 63

What is Mach bands?

Answer 63

Light and dark bands perceived at light–dark borders.

(When the transition from light to dark is gradual, rather than a step as in the Chevreul illusion, the bands are called Mach bands.)

Question 64

What is preferential looking (PL) technique?

Answer 64

A technique used to measure perception in infants. Two stimuli are presented, and the infant’s looking behavior is monitored for the amount of time the infant spends viewing each stimulus.