ch 6 sensation and perception

blind spot

the point at which the optic nerve leaves the eye, creating a "blind" spot because no receptor cells are located there.

weber's law

the principle that, to be perceived as different, two stimuli must differ by a constant minimum percentage (rather than a constant amount)

sensation

the process by which our sensory receptors and nervous represent stimulus energies from our environment

accomodation

the process by which the eye's lens changes shape to focus near or far objects on the retina.

perception

the process of organizing and interpreting sensory information, enabling to recognize meaningful objects and events

psychophysics

the study of relationships between the physical characteristics of stimuli, such as their intensity, and our psychological experience of them

Does perceptual set involve bottom-up or top-down processing? Why?

It involves top-down processing, because it draws on your experiences, assumptions, and expectations when interpreting stimuli.

LOQ 6-11 How does the brain use parallel processing to construct visual perceptions?

Through parallel processing, the brain handles many aspects of vision (color, movement, form, and depth) simultaneously. Other neural teams integrate the results, comparing them with stored information and enabling perceptions.

monocular cue

a depth cue, such as interposition or linear perspective, available to either eye alone.

binocular cue

a depth cue, such as retinal disparity, that depends on the use of two eyes.

visual cliff

a laboratory device for testing depth perception in infants and young animals.

perceptual set

a mental predisposition to perceive one thing and not another

Two examples of ___________ depth cues are interposition and linear perspective.

monocular

parallel processing

processing many aspects of a problem simultaneously; the brain's natural mode of information processing for many functions, including vision.

Cats are able to open their___________much wider than we can, which allows more light into their eyes so they can see better at night.

pupils

bottom up processing

starts at your sensory receptors and works up to higher levels of processing analysis that begins with the sensory receptors and works up to the brain's integration of sensory information

perceptual adaptation

the ability to adjust to changed sensory input, including an artificially displaced or even inverted visual field.

depth perception

the ability to see objects in three dimensions although the images that strike the retina are two-dimensional; allows us to judge distance.

priming

the activation, often unconsciously, of certain associations, thus predisposing one's perception, memory, or response

intensity

the amount of energy in a light wave or sound wave, which influences what we perceive as brightness or loudness. Intensity is determined by the wave's amplitude (height).

fovea

the central focal point in the retina, around which the eye's cones cluster.

hue

the dimension of color that is determined by the wavelength of light; what we know as the color names blue, green, and so forth.

retina

the light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information.

difference threshold

the minimum difference between two stimuli required for detection 50 percent of the time. We experience the difference threshold as a just noticeable difference (or jnd)

absolute threshold

the minimum stimulus energy needed to detect a particular stimulus 50 percent of the time

optic nerve

the nerve that carries neural impulses from the eye to the brain.

figure-ground

the organization of the visual field into objects (the figures) that stand out from their surroundings (the ground).

grouping

the perceptual tendency to organize stimuli into coherent groups.

Using sound as your example, explain how these concepts differ: absolute threshold, subliminal stimulation, and difference threshold.

Absolute threshold is the minimum stimulation needed to detect a particular sound (such as an approaching bike on the sidewalk behind you) 50 percent of the time. Subliminal stimulation happens when, without your awareness, your sensory system processes a sound that is below your absolute threshold. A difference threshold is the minimum difference needed to distinguish between two stimuli (such as between the sound of a bike and the sound of a runner coming up behind you).

LOQ 6-9 How do we perceive color in the world around us?

According to the Young-Helmholtz trichromatic (three-color) theory, the retina contains three types of color receptors. Contemporary research has found three types of cones, each most sensitive to the wavelengths of one of the three primary colors of light (red, green, or blue). According to Hering's opponent-process theory, there are three additional color processes (red-versus-green, blue-versus-yellow, black-versus-white). Research has confirmed that, en route to the brain, neurons in the retina and the thalamus code the color-related information from the cones into pairs of opponent colors. These two theories, and the research supporting them, show that color processing occurs in two stages.

LOQ 6-13 How do we use binocular and monocular cues to see in three dimensions, and how do we perceive motion?

Depth perception is our ability to see objects in three dimensions and judge distance. The visual cliff and other research demonstrate that many species perceive the world in three dimensions at, or very soon after, birth. Binocular cues, such as retinal disparity, are depth cues that rely on information from both eyes. Monocular cues (such as relative height, relative size, interposition, relative motion, linear perspective, and light and shadow) let us judge depth using information transmitted by only one eye. As objects move, we assume that shrinking objects are retreating and enlarging objects are approaching. The brain computes motion imperfectly, with young children especially at risk of incorrectly perceiving approaching hazards such as vehicles. A quick succession of images on the retina can create an illusion of movement, as in stroboscopic movement or the phi phenomenon.

LOQ 6-15 What does research on restored vision, sensory restriction, and perceptual adaptation reveal about the effects of experience on perception?

Experience guides our perceptual interpretations. People blind from birth who gained sight after surgery lack the experience to visually recognize shapes and forms. Sensory restriction research indicates that there is a critical period for some aspects of sensory and perceptual development. Without early stimulation, the brain's neural organization does not develop normally. People given glasses that shift the world slightly to the left or right, or even upside down, experience perceptual adaptation. They are initially disoriented, but they manage to adapt to their new context.

LOQ 6-10 Where are feature detectors located, and what do they do?

Feature detectors, specialized nerve cells in the visual cortex, respond to specific features of the visual stimulus, such as shape, angle, or movement. Feature detectors pass information on to other cortical areas, where supercell clusters respond to more complex patterns.

LOQ 6-12 How did the Gestalt psychologists understand perceptual organization, and how do figure-ground and grouping principles contribute to our perceptions?

Gestalt psychologists searched for rules by which the brain organizes fragments of sensory data into gestalts, or meaningful forms. In pointing out that the whole may exceed the sum of its parts, they noted that we filter sensory information and construct our perceptions. To recognize an object, we must first perceive it (see it as a figure) as distinct from its surroundings (the ground). We bring order and form to stimuli by organizing them into meaningful groups, following such rules as proximity, continuity, and closure.

What do we mean when we say that, in perception, "the whole may exceed the sum of its parts"?

Gestalt psychologists used this saying to describe our perceptual tendency to organize clusters of sensations into meaningful forms or coherent groups.

LOQ 6-8 How do the rods and cones process information, and what is the path information travels from the eye to the brain?

Light entering the eye triggers chemical changes that convert light energy into neural impulses. Cones and rods at the back of the retina each provide a special sensitivity— cones to detail and color, rods to faint light and peripheral motion. After processing by bipolar and ganglion cells, neural impulses travel from the retina through the optic nerve to the thalamus, and on to the visual cortex.

What is the rapid sequence of events that occurs when you see and recognize a friend?

Light waves reflect off the person and travel into your eyes. Receptor cells in your retina convert the light waves' energy into millions of neural impulses sent to your brain. Your brain's detector cells and work teams process the subdimensions of this visual input—including color, movement, form, and depth—separately but simultaneously. Your brain interprets this information, based on previously stored information and your expectations, and forms a conscious perception of your friend.

LOQ 6-3 How do absolute thresholds and difference thresholds differ?

Our absolute threshold for any stimulus is the minimum stimulation necessary for us to be consciously aware of it 50 percent of the time. Signal detection theory predicts how and when we will detect a faint stimulus amid background noise. Individual absolute thresholds vary, depending on the strength of the signal and also on our experience, expectations, motivation, and alertness. Our difference threshold (also called the just noticeable difference, or jnd) is the difference we can discern between two stimuli 50 percent of the time. Weber's law states that two stimuli must differ by a constant minimum percentage (not a constant amount) to be perceived as different.

LOQ 6-2 What three steps are basic to all our sensory systems?

Our senses (1) receive sensory stimulation (often using specialized receptor cells); (2) transform that stimulation into neural impulses; and (3) deliver the neural information to the brain. Transduction is the process of converting one form of energy into another. Researchers in psychophysics study the relationships between stimuli's physical characteristics and our psychological experience of them.

LOQ 6-14 How do perceptual constancies help us construct meaningful perceptions?

Perceptual constancies, such as in color, brightness (or lightness), shape, or size enable us to perceive objects as stable despite the changing image they cast on our retinas. Our brain constructs our experience of an object's color or brightness through comparisons with other surrounding objects. Knowing an object's size gives us clues to its distance; knowing its distance gives clues about its size, but we sometimes misread monocular distance cues and reach the wrong conclusions, as in the Moon illusion.

LOQ 6-6 How do our expectations, contexts, motivation, and emotions influence our perceptions?

Perceptual set is a mental predisposition that functions as a lens through which we perceive the world. Our learned concepts (schemas) prime us to organize and interpret ambiguous stimuli in certain ways. Our motivation, as well as our physical and emotional context, can create expectations and color our interpretation of events and behaviors.

What is the rough distinction between sensation and perception?

Sensation is the bottom-up process by which your sensory receptors and nervous system receive and represent stimuli. Perception is the top-down process by which your brain creates meaning by organizing and interpreting what your senses detect.

LOQ 6-1 What are sensation and perception? What do we mean by bottom-up processing and top-down processing?

Sensation is the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment. Perception is the process of organizing and interpreting this information, enabling recognition of meaningful events. Sensation and perception are one continuous process. Bottom-up processing is sensory analysis that begins at the entry level, with information flowing from the sensory receptors to the brain. Top-down processing is information processing guided by highlevel mental processes, as when we construct perceptions by filtering information through our experience and expectations.

LOQ 6-5 What is the function of sensory adaptation?

Sensory adaptation (our diminished sensitivity to constant or routine odors, sounds, and touches) focuses our attention on informative changes in our environment.

What are two key theories of color vision? Are they contradictory or complementary? Explain.

The Young-Helmholtz trichromatic theory shows that the retina contains color receptors for red, green, and blue. The opponent-process theory shows that we have opponentprocess cells in the retina and thalamus for red-green, yellow-blue, and white-black. These theories are complementary and outline the two stages of color vision: (1) The retina's receptors for red, green, and blue respond to different color stimuli. (2) The receptors' signals are then processed by the opponent-process cells on their way to the visual cortex in the brain.

wavelength

The distance from the peak of one light or sound wave to the peak of the next. Electromagnetic wavelengths vary from the short blips of gamma rays to the long pulses of radio transmission.

Why is it that after wearing shoes for a while, you cease to notice them (until questions like this draw your attention back to them)?

The shoes provide constant stimulation. Thanks to sensory adaptation, we tend to focus primarily on changing stimuli.

How do we normally perceive depth?

We are normally able to perceive depth thanks to (1) binocular cues (such as retinal disparity), and (2) monocular cues (which include relative height, relative size, interposition, linear perspective, light and shadow, and relative motion).

LOQ 6-4 How are we affected by subliminal stimuli?

We do sense some stimuli subliminally—less than 50 percent of the time—and can be affected by these sensations. But although we can be primed, subliminal sensations have no powerful, enduring influence.

LOQ 6-7 What are the characteristics of the energy that we see as visible light? What structures in the eye help focus that energy?

What we see as light is only a thin slice of the broad spectrum of electromagnetic energy. The portion visible to humans extends from the blue-violet to the red light wavelengths. After entering the eye through the cornea, passing through the pupil and iris, and being focused by a lens, light energy particles strike the eye's inner surface, the retina. The hue we perceive in a light depends on its wavelength, and its brightness depends on its intensity.

There are no receptor cells where the optic nerve leaves the eye. This creates a blind spot in your vision. To demonstrate, close your left eye, look at the spot above, and move your face away until one of the cars disappears. (Which one do you predict it will be?) Repeat with your right eye closed—and note that now the other car disappears. Can you explain why?

Your blind spot is on the nose side of each retina, which means that objects to your right may fall onto the right eye's blind spot. Objects to your left may fall on the left eye's blind spot. The blind spot does not normally impair your vision, because your eyes are moving and because one eye catches what the other misses. Moreover, even with only one eye open, our brain gives us a perception without a hole in it.

What mental processes allow you to perceive a lemon as yellow?

Your brain constructs this perception of color in two stages. In the first stage, the lemon reflects light energy into your eyes, where it is transformed into neural messages. Three sets of cones, each sensitive to a different light frequency (red, blue, and green) process color. In this case, the light energy stimulates both red-sensitive and green-sensitive cones. In the second stage, opponent-process cells sensitive to paired opposites of color (red-green, yellow-blue, and black-white) evaluate the incoming neural messages as they pass through your optic nerve to the thalamus and visual cortex. When the yellow-sensitive opponent-process cells are stimulated, you identify the lemon as yellow.

retinal disparity

a binocular cue for perceiving depth. By comparing retinal images from the two eyes, the brain computes distance—the greater the disparity (difference) between the two images, the closer the object.

signal detection theory

a theory predicting how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise). Assumes there is no single absolute threshold and that detection depends partly on a person's experience, expectations, motivation, and alertness

The amplitude of a light wave determines our perception of a. brightness. b. color. c. meaning. d. distance.

a. brightness.

Our perceptual set influences what we perceive. This mental tendency reflects our a. experiences, assumptions, and expectations. b. sensory adaptation. c. priming ability. d. difference thresholds.

a. experiences, assumptions, and expectations.

In listening to a concert, you attend to the solo instrument and perceive the orchestra as accompaniment. This illustrates the organizing principle of a. figure-ground. b. shape constancy. c. grouping. d. depth perception.

a. figure-ground.

phi phenomenon

an illusion of movement created when two or more adjacent lights blink on and off in quick succession.

gestalt

an organized whole. Gestalt psychologists emphasized our tendency to integrate pieces of information into meaningful wholes.

Weber's law states that for a difference to be perceived, two stimuli must differ by a. a fixed or constant energy amount. b. a constant minimum percentage. c. a constantly changing amount. d. more than 7 percent.

b. a constant minimum percentage.

Sensation is to _______________ as perception is to _________________. a. absolute threshold; difference threshold b. bottom-up processing; top-down processing c. interpretation; detection d. grouping; priming

b. bottom-up processing; top-down processing

The visual cliff experiments suggest that a. infants have not yet developed depth perception. b. crawling human infants and very young animals perceive depth. c. we have no way of knowing whether infants can perceive depth. d. unlike other species, humans are able to perceive depth in infancy.

b. crawling human infants and very young animals perceive depth.

Perceiving a tomato as consistently red, despite lighting shifts, is an example of a. shape constancy. b. perceptual constancy. c. a binocular cue. d. continuity.

b. perceptual constancy.

After surgery to restore vision, adults who had been blind from birth had difficulty a. recognizing objects by touch. b. recognizing objects by sight. c. distinguishing figure from ground. d. distinguishing between bright and dim light.

b. recognizing objects by sight.

subliminal

below one's absolute threshold for conscious awareness

Cones are the eye's receptor cells that are especially sensitive to ____________ light and are responsible for our ___________ vision. a. bright; black-and-white b. dim; color c. bright; color d. dim; black-and-white

c. bright; color

Depth perception underlies our ability to a. group similar items in a gestalt. b. perceive objects as having a constant shape or form. c. judge distances. d. fill in the gaps in a figure.

c. judge distances.

The blind spot in your retina is located where a. there are rods but no cones. b. there are cones but no rods. c. the optic nerve leaves the eye. d. the bipolar cells meet the ganglion cells.

c. the optic nerve leaves the eye.

top down processing

constructs perceptions from this sensory input by drawing on your experience and expectations information processing guided by higher-level mental processes, as when we construct perceptions drawing on our experience and expectations

transduction

conversion of one form of energy into another. In sensation, the transforming of stimulus energies, such as sights, sounds, and smells, into neural impulses our brain can interpret

Subliminal stimuli are a. too weak to be processed by the brain. b. consciously perceived more than 50 percent of the time. c. strong enough to affect our behavior at least 75 percent of the time. d. below our absolute threshold for conscious awareness.

d. below our absolute threshold for conscious awareness.

Our tendencies to fill in the gaps and to perceive a pattern as continuous are two different examples of the organizing principle called a. interposition. b. depth perception. c. shape constancy. d. grouping.

d. grouping.

Sensory adaptation helps us focus on a. visual stimuli. b. auditory stimuli. c. constant features of the environment. d. important changes in the environment.

d. important changes in the environment.

Two theories together account for color vision. The Young-Helmholtz trichromatic theory shows that the eye contains ___________, and Hering's theory accounts for the nervous system's having ______________. a. opposing retinal processes; three pairs of color receptors b. opponent-process cells; three types of color receptors c. three pairs of color receptors; opposing retinal processes d. three types of color receptors; opponent-process cells

d. three types of color receptors; opponent-process cells

sensory adaptation

diminished sensitivity as a consequence of constant stimulation

The cells in the visual cortex that respond to certain lines, edges, and angles are called ___________ __________.

feature detectors

In terms of perception, a band's lead singer would be considered ____________ (figure/ground), and the other musicians would be considered ______________ (figure/ground).

figure; ground.

Another term for difference threshold is the __________ __________ __________.

just noticeable difference

feature detectors

nerve cells in the brain that respond to specific features of the stimulus, such as shape, angle, or movement.

The brain's ability to process many aspects of an object or a problem simultaneously is called ____________ __________.

parallel processing

perceptual constancy

perceiving objects as unchanging (having consistent color, brightness, shape, and size) even as illumination and retinal images change.

The process by which we organize and interpret sensory information is called ________________.

perception

In experiments, people have worn glasses that turned their visual fields upside down. After a period of adjustment, they learned to function quite well. This ability is called ____________ __________.

perceptual adaptation

cones

retinal receptors that are concentrated near the center of the retina and that function in daylight or in well-lit conditions. Cones detect fine detail and give rise to color sensations.

rods

retinal receptors that detect black, white, and gray, and are sensitive to movement; necessary for peripheral and twilight vision, when cones don't respond.

Some nocturnal animals, such as toads, mice, rats, and bats, have impressive night vision thanks to having many more___________(rods/cones) than___________(rods/cones) in their retinas. These creatures probably have very poor___________(color/black-and-white) vision.

rods; cones; color.

sensory receptors

sensory nerve endings that respond to stimuli

opponent-process theory

the theory that opposing retinal processes (redgreen, yellow-blue, white-black) enable color vision. For example, some cells are stimulated by green and inhibited by red; others are stimulated by red and inhibited by green.

Young-Helmholtz trichromatic (three-color) theory

the theory that the retina contains three different types of color receptors—one most sensitive to red, one to green, one to blue—which, when stimulated in combination, can produce the perception of any color.

The characteristic of light that determines the color we experience, such as blue or green, is _____________.

wavelength