Chapter 4

Question 1

Sensation

Answer 1

Sensation is the activation of the sense organs by a source of physical energy.

Question 2

Perception

Answer 2

Perception is the sorting out, interpretation, analysis, and integration of stimuli carried out by the sense organs and brain.

Question 3

Stimulus

Answer 3

A stimulus is any passing source of physical energy that produces a response in a sense organ.
Stimuli vary in both type and intensity. Different types of stimuli activate different sense organs.

Question 4

Psychophysics

Answer 4

Psychophysics is the study of the relationship between the physical aspects of stimuli and our psychological experience of them.

Question 5

Absolute threshold

Answer 5

An absolute threshold is the smallest intensity of a stimulus that must be present for it to be detected.
Normally our senses cannot detect stimulation quite as well because of the presence of noise.

Question 6

Noise

Answer 6

Noise, as defined by psychophysicists, is the background stimulation that interferes with the perception of other stimuli.
Similarly, we have limited ability to concentrate on several stimuli simultaneously.

Question 7

Difference threshold

Answer 7

A difference threshold is the smallest level of added or reduced stimulation required to sense that a change in stimulation has occurred.
The difference threshold is the minimum change in stimulation required to detect the difference between two-stimuli, and so it also is called a just noticeable difference.

Question 8

Weber’s law

Answer 8

The size of a stimulus that constitutes a noticeable difference depends on the initial intensity of the stimulus. The relationship between changes in the original size of a stimulus and the degree to which a change will be noticed forms one of the basic laws of psychophysics: Weber’s law. Weber’s law states that a just noticeable difference is a constant proportion of the intensity of an initial stimulus (rather than a constant amount).

Question 9

Adaptation

Answer 9

Adaptation is an adjustment in sensory capacity after prolonged exposure to unchanging stimuli. Adaptation occurs as people become accustomed to a stimulus and change their frame of reference. In a sense, our brain mentally turns down the volume of the stimulation that it’s experiencing.
The apparent decline in sensitivity to sensory stimuli is due to the inability of the sensory nerve receptors to fire off messages to the brain indefinitely. Because these receptor cells are most responsive to change in stimulation, constant stimulation is not effective in producing a sustained reaction.

Question 10

Light

Answer 10

Vision starts with light, the physical energy that stimulates the eye. Light is a form of electromagnetic radiation waves that are measured in wavelengths. The sizes of wavelengths correspond to different types of energy.

Question 11

Cornea

Answer 11

The ray of light being reflected off an object first travels through the cornea, a transparent, protective window. The cornea, because of its curvature, bends (or refracts) light as it passes through, playing a primary role in focusing the light more sharply.

Question 12

Pupil

Answer 12

After moving through the cornea, the light traverses the pupil. The pupil is a dark hole in the center of the iris. The size of the pupil opening depends on the amount of light in the environment. The dimmer the surroundings are, the more the pupil opens to allow more light to enter.

Question 13

Iris

Answer 13

The iris is the colored part of the eye, which in humans ranges from a light blue to a dark brown.

Question 14

Retina

Answer 14

The retina is the part of the eye that converts the electromagnetic energy of light to electrical impulses for transmission to the brain.
Interestingly, as the image travels through the lens, it has reversed itself. Consequently, the image reaches the retina upside down (relative to its original position). Although it might seem that this reversal would cause difficulties in understanding and moving about the world, this is not the case. The brain automatically interprets the image in terms of its original position.
The retina consists of a thin layer of nerve cells at the back of the eyeball. There are two kinds of light-sensitive cells in the retina. The names they have been given describe their shapes: rods and cones.

Question 15

Rods

Answer 15

Rods are thin, cylindrical receptor cells that are highly sensitive to light.

Question 16

Cones

Answer 16

Cones are typically cone-shaped, light-sensitive receptor cells that are responsible for sharp focus and color perception, particularly in bright light.

Question 17

Fovea

Answer 17

The rods and cones are distributed unevenly throughout the retina. Cones are concentrated on the part of the retina called the fovea. The fovea is a particularly sensitive region of the retina. If you want to focus on something of particular interest, you will automatically try to center the image on the fovea to see it more sharply.

Question 18

Rods vs cones

Answer 18

The rods and cones not only are structurally dissimilar but they also play distinctly different roles in vision. Cones are primarily responsible for the sharply focused perception of color, particularly in brightly lit situations; rods are related to vision in dimly lit situations and are largely insensitive to color and to details as sharp as those the cones are capable of recognizing.
The rods play a key role in peripheral vision- seeing objects that are outside the main center of focus- and in night vision.

Question 19

Dark adaptation

Answer 19

Rods and cones also are involved in dark adaptation, the phenomenon of adjusting to dim light after being in brighter light. (Think of the experience of walking into a dark movie theater and groping your way to a seat but a few minutes later seeing the seats quite clearly.) The speed at which dark adaptation occurs is a result of the rate of change in the chemical composition of the rods and cones. Although the cones reach their greatest level of adaptation in just a few minutes, the rods take 20 to 30 minutes to reach the maximum level.

Question 20

Light adaptation

Answer 20

The opposite phenomenon of dark adaptation- light adaptation, or the process of adjusting to bright light after exposure to dim light- occurs much faster, taking only a minute or so.

Question 21

What happens when light energy strikes the retina?

Answer 21

What happens when light energy strikes the retina depends in part on whether it encounters a rod or a cone. Rods contain rhodopsin, a complex reddish-purple protein whose composition changes chemically when energized by light. The substance in cone receptors is different, but the principles are similar. Stimulation of the nerve cells in the eye triggers a neural response that is transmitted to other nerve cells in the retina called bipolar cells and ganglion cells.

Question 22

Bipolar cells & ganglion cells

Answer 22

Bipolar cells receive information directly from the rods and cones and communicate that information to the ganglion cells. The ganglion cells collect and summarize visual information, which is then moved out of the back of the eyeball and sent to the brain through a bundle of ganglion axons called the optic nerve.
Because the opening for the optic nerve passes through the retina, there are no rods or cones in the area, and that creates a blind spot. Normally, however, this absence of nerve cells does not interfere with vision because you automatically compensate for the missing part of your field of vision.

Question 23

Visual cortex

Answer 23

The ultimate processing of visual images take place in the visual cortex of the brain, and it is here that the most complex kinds of processing occur.

Question 24

Feature detector

Answer 24

Psychologists David Hubel and Torsten Wiesel won the Nobel Prize in 1981 for their discovery of feature detectors. Feature detectors are extraordinarily specialized neurons that are activated only by visual stimuli having particular features, such as a particular shape or pattern.
For instance, some feature detectors are activated only by lines of a particular width, shape, or orientation.
More recent work has added to our knowledge of the complex ways in which visual information coming from individual neurons is combined and processed. Different parts of the brain process nerve impulses simulatenously according to the attirbutes of the image. For instance, one brain system processes shape, one processes color, and others process movement, location, and depth. Furthermore, different parts of the brain are involved in the perception of specific kinds of stimuli, showing distinctions, for example, between the perception of human faces, animals, and inatimate stimuli.

Question 25

Color blindness

Answer 25

Approximately 7% of men and 0.4% of women are color blind. For most people with color-blindness, the world looks quite dull. In fact, in the most common form of color-blindness, all red and green objects are seen as yellow. In other forms of color-blindness, people are unable to tell the difference between yellow and blue. In the most extreme cases of color-blindness, which are quite rare, people perceive no color at all. To such individuals, the world looks something like the picture on an old black-and-white TV.

Question 26

Trichromatic theory of color vision

Answer 26

The trichromatic theory of color vision, which was first processed by Thomas Young and extended by Hermann von Helmholtz in the first half of the 1800s, suggests that there are three kinds of cones in the retina, each of which responds primarily to a specific range of wavelengths. One is most responsive to blue-violet colors, one to green, and the third to yellow-red. According to the trichromatic theory, perception of color is influenced by the relative strength with which each of the three kinds of cones is activated. If we see a blue sky, the blule-violet cones are primarily triggered, and the others show less activity.

Question 27

Opponent-process theory of color vision

Answer 27

The fact that the colors in the afterimage are different from those in the original calls into question the trichromatic theory, which has led scientists to develop alternative explanations for color vision. According to the opponent-process theory of color vision, first proposed by German physiologist Ewald Hering in the 19th century, receptor cells are linked in pairs, working in opposition to each other. Specifically, there are a blue-yellow pairing, and a red-green pairing, and a black-white pairing. If an object reflects light that contains more blue than yellow, it will stimulate the firing of the cells sensitive to blue, simultaneously discouraging or inhibiting the firing of receptor cells sensitive to yellow- and the object will appear blue. If, in contrast, a light contains more yellow than blue, the cells that respond to yellow will be stimulated to fire while the blue ones are inhibited, and the object will appear yellow.

Question 28

Sound

Answer 28

Sound is the movement of air molecules brought by a source of vibrations.

Question 29

Eardrum

Answer 29

The eardrum is the part of the ear that vibrates when sound waves hit it. The more intense the sound, the more the eardrum vibrates. These vibrations are then transferred into the middle ear, a tiny chamber containing three bones (the hammer, the anvil, and the stirrup) that transmit vibrations to the oval window, a thin membrane leading to the inner ear.

Question 30

The inner ear

Answer 30

The inner ear is the portion of the ear that changes the sound into a form in which they can be transmitted to the brain. When sound enters the inner ear through the oval window, it moves into the cochlea, a coiled tube that looks something like a snail and is filled with fluid that vibrates in response to sound. Inside the cochlea is the basilar membrane, a structure that runs through the center of the choclea, dividing it itnoa n upper chamber and a lower chamber.

Question 31

Frequency

Answer 31

Frequency is the number of wave cycles that occur in a second. At very low frequencies there are relatively few wave cycles per second. Low frequencies are translated into a sound that is very low in pitch (Pitch is the characteristic that makes sound seem "high" or "low".)

Question 32

Amplitude

Answer 32

Amplitude is a feature of wave patterns that allows us to distinguish between loud and soft sounds. We are sensitive to broad variations in sound amplitudes.

Question 33

How are our brains able to sort out wavelengths of different frequencies and intensities?

Answer 33

One clue comes from studies of the basilar membrane, the area in the cochlea that translates physical vibrations into neural impulses. It turns out that sounds affect different areas of the basilar membrane, depending on the frequency of the sound wave. The part of the basilar membrane nearest to the oval window is most sensitive to high-frequency sounds, and the part nearest to the cochlea's inner end is most sensitive to low-frequency sounds. This finding has led to the place theory of hearing.

Question 34

Place theory of hearing

Answer 34

The place theory of hearing states that different areas of the basilar membrane respond to different frequencies.

Question 35

Frequent theory of hearing

Answer 35

Place theory does not tell the full story of hearing, because very low frequency sounds trigger neurons across such a wide area of the basilar membrane that no single site is involved. Consequently, an additional explanation for hearing has been proposed: frequency theory. The frequency theory of hearing suggests that the entire basilar membrane acts as a microphone, vibrating as a whole in response to a sound. Neither place theory nor frequency theory provides the full explanation for hearing. Place theory provides a better explanation for the sensing of high-frequency sounds, whereas frequency theory explains what happens when low-frequency sounds are encountered. Medium-frequency sounds incorporate both processes.

Question 36

Otholiths

Answer 36

The pull on our bodies caused by the acceleration of forward, backward, or up-and-down motion, as well as the constant pull of gravity, is sensed by the otholiths, tiny, motion-sensitive crystals in the semicircular canals.

Question 37

Olfactory cells

Answer 37

The sense of smell is sparked when the molecules of a substance enter the nasal passages and meet olfactory cells, the receptor neurons of the nose, which are spread across the nasal cavity. More than 1,000 separate types of receptors have been identified on those cells so far. Each of these receptors is so specialized that it responds only to a small band of different odors.

Question 38

Taste

Answer 38

The sense of taste (gustation) involves receptor cells that respond to four basic stimulus qualities: sweet, sour, salty, and bitter. A fifth category also exists, a flavor called umami, although there is controversy about whether it qualifies as a fundamental taste. Umami is a hard-to-translate Japanese word, although the English "meaty" or "savory" comes close. Chemically, umami involves food stimuli that contain amino acids. The receptor cells for taste are located in roughly 10,000 taste buds, which are distributed across the tongue and other parts of the mouth and throat.

Question 39

Skin senses

Answer 39

All our skin senses- touch, pressure, temperature, and pain- play a critical role in survival, making us aware of potential danger to our bodies. Most of these senses operate through nerve receptor cells located at various depths throughout the skin, distributed unevenly throughout the body. For example, some areas, such as the fingertips, have many more receptor cells sensitive to touch and as a consequence are notably more sensitive than other areas of the body.

Question 40

Substance P

Answer 40

One explanation for pain is that it is an outcome of cell injury; when a cell is damaged, regardless of the source of damage, it releases a chemical called substance P that transmits pain messages to the brain.

Question 41

Gate-control theory of pain

Answer 41

According to the gate-control theory of pain, particular nerve receptors in the spinal cord lead to specific areas of the brain related to pain. The gate can be shut in two different ways: First, other impulses can overwhelm the nerve pathways relating to pain, which are spread throughout the brain. In this case, nonpainful stimuli compete with and sometimes displace the neural message of pain, thereby shutting off the painful stimulus. This explains why rubbing the skin around an injury (or even listening to distracting music) helps reduce pain. The competing stimuli can overpower the painful ones. Psychological factors account for the second way the gate can be shut.

Question 42

Gestalt laws organization

Answer 42

Some of the most basic perceptual processes can be described by a series of principles that focus on the ways we organize bits and pieces of information into meaningful wholes. Known as gestalt laws of organization, these principles were set forth in the early 1900s by a group of German psychologists who studdies paterns, or gestalts.

Question 43

Top-down processing

Answer 43

In top-down processing, perception is guided by higher-level knowledge, experience, and motivations.

Question 44

Bottom-up processing

Answer 44

Bottom-up processing consists of the progression of recognizing and processing information from individual components of a stimuli and moving to the perception of the whole.

Question 45

Depth perception

Answer 45

The ability to view the world in three dimensions and to perceive distance- a skill known as depth perception- is due largely to the fact that we have two eyes. Because there is a certain distance between the eyes, a slightly different images reaches each retina. The brain integrates the two images into one view, but it also recognizes the difference in images and uses this difference to estimate the distance of an object from us. The difference in the images seen by the left eye and the right eye is known as binocular disparity.