Find study materials for any course. Check these out:
Browse by school
Make your own
To login with Google, please enable popups
To login with Google, please enable popups
Don’t have an account?
To signup with Google, please enable popups
To signup with Google, please enable popups
Sign up withor
What three steps are basic to all our sensory systems?
receive sensory stimulation, often using specialized receptor cells.
transform that stimulation into neural impulses.
deliver the neural information to our brain.
the study of relationships between the physical characteristics of stimuli, such as their intensity, and our psychological experience of them
the minimum stimulus energy needed to detect a particular stimulus 50 percent of the time.
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.
below one’s absolute threshold for conscious awareness.
the activation, often unconsciously, of certain associations, thus predisposing one’s perception, memory, or response.
How can we feel or respond to what we do not know and cannot describe?
an imperceptibly brief stimulus often triggers a weak response that can be detected by brain scanning
The stimulus may reach consciousness only when it triggers synchronized activity in multiple brain areas
Such experiments reveal the dual-track mind at work: Much of our information processing occurs automatically, out of sight, off the radar screen of our conscious mind.
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).
that difference threshold increases with the size of the stimulus. If we listen to our music at 40 decibels, we might detect an added 5 decibels. But if we increase the volume to 110 decibels, we probably won’t detect
a 5 decibel change.
In the late 1800s, Ernst Weber noted something so simple and so widely applicable that we still refer to it as 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).
Two lights, for example, must differ in intensity by 8 percent. Two objects must differ in weight by 2 percent. And two tones must differ in frequency by only 0.3 percent
diminished sensitivity as a consequence of constant stimulation.
When we are constantly exposed to an unchanging stimulus, we become less aware of it because our nerve cells fire less frequently.
Why, then, if we stare at an object without flinching, does it not vanish from sight?
Because, unnoticed by us, our eyes are always moving. This continual flitting from one spot to another ensures that stimulation on the eyes’ receptors continually changes
What if we actually could stop our eyes from moving? Would sights seem to vanish, as odors do?
To find out, psychologists have devised ingenious instruments that maintain a constant image on the eye’s inner surface.
Although sensory adaptation reduces our sensitivity, it offers an important benefit: freedom to focus on informative changes in our environment without being distracted by background chatter.
stinky or heavily perfumed people don’t notice their odor
because, like you and me, they adapt to what’s constant and detect only change.
Our sensory receptors are alert to novelty; bore them with repetition and they free our attention for more important things.
The point to remember:
We perceive the world not exactly as it is, but as it is useful for us to perceive it.
Sensory adaptation even influences how we per- ceive emotions. By creating a 50-50 morphed blend of an angry face and a scared face, researchers showed that our visual system adapts to a static facial expression by becoming less responsive to it
Perceptual set can also affect what we hear.
Perceptual set similarly affects taste.
What determines our perceptual set?
Through experience we form concepts, or schemas, that organize and interpret unfamiliar information.
OUR EYES RECEIVE LIGHT ENERGY and transduce (transform) it into neural messages that our brain then processes into what we consciously see.
Two physical characteristics of light help determine our sensory experience.
Light’s wavelength—the distance from one wave peak to the next determines its hue (the color we experience, such as the tulip’s red petals or green leaves). Intensity—the amount of energy in light waves (determined by a wave’s amplitude, or height)—influences brightness.
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 cosmic rays to the long pulses of radio transmission.
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 influ- ences what we perceive as brightness or loudness. Intensity is determined by the wave’s amplitude (height).
Light enters the eye through the cornea, which bends light to help provide focus
The light then passes through the pupil, a small adjustable open- ing.
a ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening.
The iris also responds to our cognitive and emotional states. When you feel disgust or you are about to answer No to a question, your pupils constrict
feeling amorous, your telltale dilated pupils and dark eyes subtly signal your interest. Each iris is so distinctive that an iris-scanning machine can confirm your identity.
Behind the pupil is a transparent lens that focuses incoming light rays into an image on the retina, a multilayered tissue on the eyeball’s sensitive inner surface.
the transparent structure behind the pupil that changes shape to help focus images on the 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.
The lens focuses the rays by changing its curvature and thickness in a process called accommodation.
the process by which the eye’s lens changes shape to focus near or far objects on the retina.
Imagine that you could follow behind a single light-energy particle after it entered your eye.
First, you would thread your way through the retina’s sparse outer layer of cells. Then, reaching the back of the eye, you would encounter its buried receptor cells, the rods and cones
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 and that function in daylight or in well-lit conditions. The cones detect fine detail and give rise to color sensations.
There, you would see the light energy trigger chemical changes.
That chemical reaction would spark neural signals, activating nearby bipolar cells. The bipolar cells in turn would activate the neighboring ganglion cells, whose axons twine together like the strands of a rope to form the optic nerve
the nerve that carries neural impulses from the eye to the brain.
The optic nerve is an information highway to your brain, where your thalamus stands ready to distribute the information it receives from your eyes. The optic nerve can send nearly 1 million mes- sages at once through its nearly 1 million ganglion fibers.
Where the optic nerve leaves the eye, there are no receptor cells—creating a blind spot. Close one eye and you won’t see a black hole, however. Without seeking your approval, your brain fills in the hole.
the point at which the optic nerve leaves the eye, creating a “blind” spot because no receptor cells are located there.
Rods and cones differ in where they’re found and in what they do
Cones cluster in and around the fovea, the retina’s area of central focus. Many cones have their own hotline to the brain: Each cone transmits its message to a single bipolar cell. That cell helps relay the cone’s individual message to the visual cortex, which devotes a large area to input from the fovea. These direct connections preserve the cones’ precise information, making them better able to detect fine detail.
the central focal point in the retina, around which the eye’s cones cluster.
Rods don’t have dedicated hotlines. Rods share bipolar cells which send combined messages. To experience this rod-cone difference in sensitivity to details, pick a word in this sentence and stare directly at it, focusing its image on the cones in your fovea.
One of vision’s most basic and intriguing mysteries is how we see the world in color. In everyday conversation, we talk as though objects possess color: “A tomato is red.” Recall the old question, “If a tree falls in the forest and no one hears it, does it make a sound?” We can ask the same of color: If no one sees the tomato, is it red?
The answer is No. First, the tomato is everything but red, because it rejects (reflects) the long wavelengths of red. Second, the tomato’s color is our mental construction. As Isaac Newton (1704) noted, “The [light] rays are not colored.” Like all aspects of vision, our perception of color resides not in the object itself but in the theater of our brains, as evidenced by our dreaming in color.
Modern detective work on the mystery of color vision began in the nineteenth century, when Hermann von Helmholtz built on the insights of an English physicist, Thomas Young.
Knowing this, Young and von Helmholtz formed a hypothesis: The eye must have three corresponding types of color receptors
Young-Helmholtz trichromatic (three-color) theory
the theory that the retina contains three different 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.
Hering, a physiologist, found a clue in afterimages
Hering’s opponent-process theory.
the theory that opposing retinal processes (red- green, 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.
Recall that the thalamus relays visual information from the retina to the visual cortex. In both the retina and the thalamus, some neurons are turned “on” by red but turned “off” by green. Others are turned on by green but off by red (DeValois & DeValois, 1975). Like red and green marbles sent down a narrow tube, “red” and “green” messages cannot both travel at once. Red and green are thus opponents, so we do not experience a reddish green. But red and blue travel in separate channels, so we can see a reddish-blue magenta.
nerve cells in the brain that respond to specific features of the stimulus, such as shape, angle, or movement.
David Hubel and Torsten Wiesel (1979), who showed that our brain’s computing system deconstructs visual images and then eassembles them
Hubel and Wiesel received a Nobel Prize for their work on feature detectors, nerve cells in the brain that respond to a scene’s specific features—to particular edges, lines, angles, and movements.
Using microelectrodes, they had discovered that some neurons fired actively when cats were shown lines at one angle, while other neurons responded to lines at a differ- ent angle. They surmised that these specialized neurons in the occipital lobe’s visual cortex—now known as feature detectors—receive information from individual gan- glion cells in the retina
Feature detectors pass this specific information to other cortical areas, where teams of cells (supercell clusters) respond to more complex patterns.
One temporal lobe area by your right ear enables you to perceive faces and, thanks to a specialized neural network, to recognize them from varied view- points. If stimulated in this area, you might spontaneously see faces. If this region were damaged, you might recognize other forms and objects, but not familiar faces.
Researchers can temporarily disrupt the brain’s face-processing areas with magnetic pulses. When this happens, people cannot recognize faces, but they can recognize houses, because the brain’s face-perception occurs separately from its object-perception
our brain achieves these and other remarkable feats by parallel processing: doing many things at once. To analyze a visual scene, the brain divides it into subdimensions— motion, form, depth, color—and works on each aspect simultaneously We then construct our perceptions by integrating the separate but parallel work of these different visual teams
the processing of many aspects of a problem simultaneously; the brain’s natural mode of information processing for many functions, including vision.
To recognize a face, your brain integrates information projected by your retinas to several visual cortex areas, compares it to stored information, and enables you to recog- nize the face: Grandmother! Scientists have debated whether this stored information is contained in a single cell or, more likely, distributed over a vast network of cells. Some supercells—grandmother cells—do appear to respond very selectively to 1 or 2 faces in 100
Early in the twentieth century, a group of German psychologists noticed that when given a cluster of sensations, people tend to organize them into a gestalt, a German word meaning a “form” or a “whole.” As we look straight ahead, we cannot separate the perceived scene into our left and right fields of view. It is, at every moment, one whole, seamless scene. Our conscious perception is an integrated whole.
an organized whole. Gestalt psychologists emphasized our tendency to integrate pieces of information into meaningful wholes.
Over the years, the Gestalt psychologists demonstrated many principles we use to organize our sensations into perceptions . Underlying all of them is a fundamental truth: Our brain does more than register information about the world. Perception is not just opening a shutter and letting a picture print itself on the brain. We filter incoming information and construct perceptions. Mind matters.
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 coherent groups.
Proximity We group nearby figures together. We see not six separate lines, but three sets of two lines.
Continuity We perceive smooth, continuous patterns rather than discontinuous ones. This pattern could be a series of alternating semicircles, but we perceive it as two continuous lines—one wavy, one straight.
Closure We fill in gaps to create a complete, whole object. Thus we assume that the circles on the left are complete but partially blocked by the (illusory) triangle. Add nothing more than little line segments to close off the circles and your brain stops constructing a triangle.
the ability to see objects in three dimensions although the images that strike the retina are two- dimensional; allows us to judge distance.
Depth perception is partly innate, as Eleanor Gibson and Richard Walk (1960) discovered using a model of a cliff with a drop-off area (which was covered by sturdy glass).
a laboratory device for test- ing depth perception in infants and young animals.
depth cues, such as retinal disparity, that depend on the use of two eyes.
a binocular cue for perceiving depth: By comparing images from the retinas in the two eyes, the brain computes distance—the greater the disparity (difference) between the two images, the closer the object.
depth cues, such as interposition and linear perspective, available to either eye alone.
Our brain also perceives a rapid series of slightly varying images as continuous movement (a phenomenon called stroboscopic movement)
We perceive two adjacent stationary lights blinking on and off in quick succession as one single light moving back and forth. Lighted signs exploit this phi phenomenon with a succession of lights that creates the impression of, say, a moving arrow.
an illusion of movement created when two or more adjacent lights blink on and off in quick succession.
Its next task is to recognize objects without being deceived by changes in their color, brightness, shape, or size—a top-down process called perceptual constancy.
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 wave- lengths reflected by the objects.
Brightness constancy (also called lightness constancy) similarly depends on context. We perceive an object as having a constant brightness even while its illumination varies.
This perception of constancy depends on relative luminance the amount of light an object reflects relative to its surroundings
Shape and Size Constancies
Sometimes an object whose actual shape cannot change seems to change shape with the angle of our view. More often, thanks to shape constancy, we perceive the form of familiar objects, such as the door. as constant even while our retinas receive changing images of them. Our brain manages this feat thanks to visual cortex neurons that rapidly learn to associ- ate different views of an object
Thanks to size constancy, we perceive objects as having a constant size, even while our distance from them varies. We assume a car is large enough to carry people, even when we see its tiny image from two blocks away. This assumption also illustrates the close connection between perceived distance and perceived size.
This interplay between perceived size and perceived dis- tance helps explain several well- known illusions, including the Moon illusion: The Moon looks up to 50 percent larger when near the horizon than when high in the sky.
Philosophers have debated whether our perceptual abilities should be credited to our nature or our nurture. To what extent do we learn to perceive?
German philosopher Immanuel Kant (1724–1804) maintained that knowledge comes from our inborn ways of organizing sensory experiences.
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.
the chamber between the eardrum and cochlea containing three tiny bones (hammer, anvil, and stirrup) that concentrate the vibrations of the eardrum on the cochlea’s oval window.
a coiled, bony, fluid-filled tube in the inner ear; sound waves traveling through the cochlear fluid trigger nerve impulses.
The incoming vibrations cause the cochlea’s membrane (the oval window) to vibrate, jostling the fluid that fills the tube. This motion causes ripples in the basilar membrane, bending the hair cells lining its surface, not unlike the wind bending a wheat field.
Hair cell movement triggers impulses in the adjacent nerve cells. Axons of those cells converge to form the auditory nerve, which sends neural messages (via the thalamus) to the auditory cortex in the brain’s temporal lobe.
the innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs.
sensorineural hearing loss
the most common form of hearing loss, also called nerve deafness; caused by damage to the cochlea’s receptor cells or to the auditory nerves.
conduction hearing loss
less common form of 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.
Hermann von Helmholtz’s place theory presumes that we hear different pitches because different sound waves trigger activity at different places along the cochlea’s basilar membrane.
in hearing, the theory that links the pitch we hear with the place where the cochlea’s membrane is stimulated.
in hearing, the theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch. (Also called temporal theory.)
sensory receptors that enable the perception of pain in response to potentially harmful stimuli.
the theory that the spinal cord contains a neurological “gate” that blocks pain signals or allows them to pass on to the brain. The “gate” is opened by the activity of pain signals traveling up small nerve fibers and is closed by activity in larger fibers or by information coming from the brain.
People with hearing loss often experience the sound of silence: tinnitus, the phantom sound of ringing in the ears.
a social interaction in which one person (the hypno-tist) suggests to another (the subject) that certain perceptions, feelings, thoughts, or behaviors will spontaneously occur.
a split in consciousness, which allows some thoughts and behaviors to occur simultaneously with others.
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.
savory meaty taste
The resulting experiences of smell (olfaction) are strikingly intimate: You inhale something of whatever or whoever it is you smell.
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.
in psychological science, the influence of bodily sensa- tions, gestures, and other states on cognitive preferences and judgments.
seeing the mouth movements for ga while hearing ba we may perceive da.lip reading is part of hearing.
Sign up for free and study better.
Get started today!