Chapter 5 Psychology

Sensation and Perception

Sensation is the bottom-up process by which the physical sensory system receives and represents stimuli. Perception is the top-down mental process of organizing and interpreting sensory input.

analysis that begins with the sensory receptors and works up to the brain's integration of sensory information.

information processing guided by higher-level mental processes, as when we construct perceptions drawing on our experience and expectations.

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.

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.

We do sense some stimuli subliminally— less than 50 percent of the time—but those sensations don't have lasting behavioral effects.

We grow less sensitive to constant sensory input. This diminished sensitivity to constant or routine odors, sounds, and touches (sensory adaptation) focuses our attention on informative changes in our environment.

Perception is influenced by our perceptual set—our mental predisposition to perceive one thing and not another. Our physical, emotional, and cultural context, as well as our motivation, can create expectations about what we will perceive, thus affecting those perceptions.

The visible light we experience is just a thin slice of the broad spectrum of electromagnetic energy. The hue (blue, green, and so forth) we perceive in a light depends on its wavelength, and its brightness depends on its intensity.

Light entering the eye is focused on our retina—the inner surface of the eye. The retina's light-sensitive rods and color-sensitive cones convert the light energy into neural impulses After processing by bipolar and ganglion cells in the eyes' retina, neural impulses travel through the optic nerve to the thalamus and on to the visual cortex.

In the visual cortex, feature detectors respond to specific features of the visual stimulus, such as edges, lines, and angles. 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.

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 the opponent-process theory, there are three additional color processes (red-versus-green, blue-versus-yellow, black-versuswhite). Contemporary research has confirmed that, on the way 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.

Gestalt psychologists showed that the brain organizes bits of sensory information 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 as distinct (see it as a figure) from its surroundings (the ground). We bring order and form to sensory input by organizing it into meaningful groups, following such rules as proximity, continuity, and closure.

Humans and many other species perceive depth at, or very soon after, birth. We transform two-dimensional retinal images into three-dimensional depth perceptions that allow us to see objects in three dimensions and to judge distance. Binocular cues, such as retinal disparity, are depth cues that rely on information from both eyes. Monocular cues (such as relative size, interposition, relative height, relative motion, linear perspective, and light and shadow) let us judge depth using information transmitted by only one eye.

Perceptual constancy is our ability to recognize an object regardless of the changing image it casts upon our retinas due to its changing angle, distance, or illumination. Color constancy is our ability to perceive consistent color in an object, even though the lighting and wavelengths shift. Shape constancy is our ability to perceive familiar objects (such as an opening door) as unchanging in shape. Size constancy is our ability to perceive objects as unchanging in size despite their changing retinal images. 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.

Experience guides our perceptual interpretations. Some perceptual abilities (such as color and figure-ground perception) are inborn. But people blind from birth who gain sight after surgery lack the experience to visually recognize shapes, forms, and complete faces. 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. Given eyeglasses that shift the world slightly to the left or right, turn it upside down, or reverse it, people can, through perceptual adaptation, learn to move about with ease.

Sound waves vary in amplitude (perceived as loudness) and in frequency (perceived as pitch—a tone's highness or lowness). Sound energy is measured in decibels.

Sound waves vary in amplitude, which we perceive as differing loudness, and in frequency, which we experience as differing pitch. Through a mechanical chain of events, sound waves travel from the outer ear through the auditory canal, causing tiny vibrations in the eardrum. The bones of the middle ear transmit the vibrations to the fluid-filled cochlea in the inner ear, causing waves of movement in hair cells lining the basilar membrane. This movement triggers nerve cells to send signals along the auditory nerve to the thalamus and then to the brain's auditory cortex. Small differences in the loudness and timing of the sounds received by each ear allow us to locate sounds. Sensorineural hearing loss (or nerve deafness) results from damage to the cochlea's hair cells or their associated nerves. Conduction hearing loss results from damage to the mechanical system that transmits sound waves to the cochlea. Cochlear implants can restore hearing for some people.

Our sense of touch is actually several senses—pressure, warmth, cold, and pain—that combine to produce other sensations, such as "hot." Only pressure has identifiable receptors.

Pain reflects bottom-up sensations (such as input from nociceptors, the sensory receptors that detect hurtful temperatures, pressure, or chemicals) and top-down processes (such as experience, attention, and culture). Pain treatments often combine physical and psychological elements, including distractions. Hypnosis, which increases our response to suggestions, can help relieve pain. Posthypnotic suggestion is used by some clinicians to help control undesired symptoms and behavior.

Both taste and smell are chemical senses. Taste involves five basic sensations— sweet, sour, salty, bitter, and umami. Taste receptors in the taste buds carry messages to an area between the frontal and temporal lobes of the brain. There are no basic sensations for smell. Some 20 million olfactory receptor cells for smell, located at the top of each nasal cavity, send messages to the brain. These cells work together, combining their messages into patterns that vary, depending on the different odors they detect.

Through kinesthesia, we sense the position and movement of individual body parts. We monitor our head's (and therefore our body's) position and movement, and maintain our balance, with our vestibular sense.

Sensory interaction is the influence of one sense on another. This occurs, for example, when the smell of a favorite food enhances its taste. Embodied cognition is the influence of bodily sensations, gestures, and other states on cognitive preferences and judgments.

The three most testable forms of extrasensory perception (ESP) are telepathy (mind-to-mind communication), clairvoyance (perceiving remote events), and precognition (perceiving future events). Researchers have not been able to replicate (reproduce) ESP effects under controlled conditions.

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

the process by which our brain organizes and interprets sensory information, transforming it into meaningful objects and events.

analysis that begins with the sensory receptors and works up to the brain's integration of sensory information.

information processing guided by higher-level mental processes, as when we construct perceptions drawing on our experience and expectations.

changing 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.

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

below our absolute threshold for conscious awareness.

the activation, often unconsciously, of particular associations in memory.

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).

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

reduced sensitivity in response to constant stimulation.

a mental predisposition to perceive one thing and not another.

the distance from the peak of one light or sound wave to the peak of the next.

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

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).

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

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

retinal receptor cells that are concentrated near the center of the retina; in daylight or well-lit conditions, cones detect fine detail and give rise to color sensations.

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

the point at which the optic nerve leaves the eye; this part of the retina is "blind" because it has no receptor cells.

nerve cells in the brain that respond to specific features of a stimulus, such as edges, lines, and angles.

the processing of many aspects of a problem or scene at the same time; the brain's natural mode of information processing for many functions, including vision.

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

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

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

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

the perceptual tendency to organize stimuli into meaningful groups.

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

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

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

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

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

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

perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the object.

in vision, the ability to adjust to an artificially displaced or even inverted visual field.

the sense or act of hearing.

the number of complete wavelengths that pass a point in a given time (for example, per second).

a tone's experienced highness or lowness; depends on frequency.

a coiled, bony, fluid-filled tube in the inner ear; sound waves traveling through the cochlear fluid trigger nerve impulses.

hearing loss caused by damage to the cochlea's receptor cells or to the auditory nerves; also called nerve deafness.

hearing loss caused by damage to the mechanical system that conducts sound waves to the cochlea.

a device for converting sounds into electrical signals and stimulating the auditory nerve through electrodes threaded into the cochlea.

a social interaction in which one person (the subject) responds to a suggestion by another person (the hypnotist) that certain perceptions, feelings, thoughts, or behaviors will spontaneously occur.

a suggestion, made during a hypnosis session, to be carried out after the subject is no longer hypnotized; used by some clinicians to help control undesired symptoms and behaviors.

the system for sensing the position and movement of individual body parts.

the sense of body movement and position, including the sense of balance.

the principle that one sense may influence another, as when the smell of food influences its taste.

the influence of bodily sensations, gestures, and other states on cognitive preferences and judgments.

the controversial claim that perception can occur apart from sensory input, such as through telepathy, clairvoyance, and precognition.

b. bottom-up processing; top-down processing

perception

below our absolute threshold for conscious awareness.

just noticeable difference

a constant minimum percentage.

important changes in the environment.

experiences, assumptions, and expectations.

wavelength

brightness.

the optic nerve leaves the eye.

bright; color

feature detectors

parallel processing

three types of color receptors; opponent-process cells

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.

grouping.

figure-ground.

crawling human infants and very young animals perceive depth.

judge distances.

monocular

perceptual constancy.

recognizing objects by sight.

perceptual adaptation

Cochlea

The outer ear collects sound waves, which are translated into mechanical waves by the middle ear and turned into fluid waves in the inner ear. The auditory nerve then translates the energy into electrical waves and sends them to the brain, which perceives and interprets the sound.

pressure

We have specialized receptors for detecting sweet, salty, sour, bitter, and umami tastes. Being able to detect pleasurable tastes enabled our ancestors to seek out energy- and protein-rich foods. Detecting aversive tastes deterred them from eating toxic substances, increasing their chances of survival.

Kinesthesia; vestibular sense

Your vestibular sense regulates balance and body positioning through kinesthetic receptors triggered by fluid in your inner ear. Wobbly legs and a spinning world are signs that these receptors are still responding to the ride's turbulence. As your vestibular sense adjusts to solid ground, your balance will be restored.

sensory interaction.

None of these answers