5 Steps to a 5 AP Psychology, 2010-2011 Edition (25 page)

Do you know someone with perfect pitch? Many musicians can hear a melody, then play or sing it. Several theories attempt to explain how you can discriminate small differences in sound frequency or pitch. According to Georg von Bekesy’s
place theory
, the position on the basilar membrane at which waves reach their peak depends on the frequency of a tone. High frequencies produce waves that peak near the close end and are interpreted as high-pitched sound, while low frequency waves travel farther, peaking at the far end, and are interpreted as low-pitched sound. Place theory accounts well for high-pitched sounds. According to
frequency theory
, the rate of the neural impulses traveling up the auditory nerve matches the frequency of a tone, enabling you to sense its pitch. Individual neurons can only fire at a maximum of 1,000 times per second. A volley mechanism in which neural cells can alternate firing can achieve a combined frequency of about 4,000 times per second. The brain can read pitch from the frequency of the neural impulses. Frequency theory
together with the volley principle explains well how you hear low-pitched sounds of up to 4,000 Hz, but this theory doesn’t account for high-pitched sounds. It appears hearing intermediate-range pitches involves some combination of the place and frequency theories.

Why do hearing aids only help some deaf people? Conduction deafness and sensorineural or neural deafness have different physiological bases.
Conduction deafness
is a loss of hearing that results when the eardrum is punctured or any of the ossicles lose their ability to vibrate. People with conduction deafness can hear vibrations when they reach the cochlea by ways other than through the middle ear. A conventional hearing aid may restore hearing by amplifying the vibrations conducted by other facial bones to the cochlea.
Nerve (sensorineural) deafness
results from damage to the cochlea, hair cells, or auditory neurons. This damage may result from disease, biological changes of aging, or continued exposure to loud noise. For people with deafness caused by hair cell damage, cochlea implants can translate sounds into electrical signals, which are wired into the cochlea’s nerves, conveying some information to the brain about incoming sounds.

Just as hearing is sensitivity to pressure on receptors in the cochlea, touch is sensitivity to pressure on the skin. Psychologists often use
somatosensation
as a general term for four classes of tactile sensations: touch/pressure, warmth, cold, and pain. Other tactile sensations result from simultaneous stimulation of more than one type of receptor. For example, burning results from stimulation of warmth, cold, and pain receptors. Itching results from repeated gentle stimulation of pain receptors, a tickle results from repeated stimulation of touch receptors, and the sensation of wetness results from simultaneous stimulation of adjacent cold and pressure receptors. Transduction of mechanical energy of pressure/touch and heat energy of warmth and cold occurs at sensory receptors distributed all over the body just below the skin’s surface. Neural fibers generally carry the sensory information to your spinal cord. Information about touch usually travels quickly from your spinal cord to your medulla, where nerves criss-cross, to the thalamus, arriving at the opposite sides of your somatosensory cortex in your parietal lobes. Weber used a two-point discrimination test to determine that regions such as your lips and fingertips have a greater concentration of sensory receptors than your back. The amount of cortex devoted to each area of the body is related to the sensitivity of that area. Touch is necessary for normal development and promotes a sense of well-being.

Pathways for temperature and pain are slower and less defined. You probably have a harder time localizing where you sense warmth and pain on your skin than where you sense touch or pressure. Pain is often associated with secretion of substance P, and relief from pain is often associated with secretion of endorphins. Because the experience of pain is so variable, pain requires both a biological and psychological explanation. Ronald Melzack and Patrick Wall’s
gate-control theory
attempts to explain the experience of pain. You experience pain only if the pain messages can pass through a gate in the spinal cord on their route to the brain. The gate is opened by small nerve fibers that carry pain signals. Conditions that keep the gate open are anxiety, depression, and focusing on the pain. The gate is closed by neural activity of larger nerve fibers, which conduct most other sensory signals, or by information coming from the brain. Massage, electrical stimulation, acupuncture, ice, and the natural release of endorphins can influence the closing of the gate. The experience of pain alerts you to injury and often prevents further damage.

The body senses of kinesthesis and the vestibular sense provide information about the position of your body parts and your body movements in your environment. Close your eyes and touch your nose with your index finger.
Kinesthesis
is the system that enables you to sense the position and movement of individual parts of your body. Sensory receptors for kinesthesis are nerve endings in your muscles, tendons, and joints.

Your
vestibular sense
is your sense of equilibrium or body orientation. Your inner ear has semicircular canals at right angles to each other. Hair-like receptor cells are stimulated by acceleration caused when you turn your head. The vestibular sacs respond to straight-line accelerations with similar receptors. The combined activities of your vestibular sense, kinesthesis, and vision enable you to maintain your balance.

Gustation
(taste) and
olfaction
(smell) are called chemical senses because the stimuli are molecules. Your chemical senses are important systems for warning and attraction. You won’t eat rotten eggs or drink sour milk and you can smell smoke before a sensitive household smoke detector. Evolutionarily, these adaptations increased chances of survival.

Taste receptor cells are most concentrated on your tongue in taste buds embedded in tissue called fungiform papillae, but are also on the roof of your mouth and the opening of your throat. Tasters have an average number of taste buds, nontasters have fewer taste buds, and supertasters have the most. You can taste only molecules that dissolve in your saliva or a liquid you drink. Scientists have identified five types of taste receptors for sweet, salty, sour, bitter, and, most recently, umami or glutamate. Babies show a preference for sweet and salty, both necessary for survival; and disgust for bitter and sour, which are characteristic of poisonous and spoiled substances. Supertasters are more sensitive than others to bitter, spicy foods and alcohol, which they find unpleasant. Each receptor is sensitive to specific chemicals that initiate an action potential. The pathway for taste messages passes to the brainstem, thalamus, and primary gustatory cortex. Receptors for different tastes activate different regions of the primary taste cortex. Our tongues also have receptors for touch, pain, cold, and warmth. The sensory interaction of taste, temperature, texture, and olfaction determine flavor.

Odor molecules reach your moist olfactory epithelium high in your nasal cavity through the nostrils of your nose and the nasal pharynx linking your nose and mouth. Dissolved odor molecules bind to receptor sites of olfactory receptors, triggering an action potential. Research has not uncovered basic odors. Axons of olfactory sensory neurons pass directly into the olfactory bulbs of the brain. Sensory information about smell is transmitted to the hypothalamus and structures in the limbic system associated with memory and emotion as well as the primary cortex for olfaction on the underside of the frontal lobes, but not the thalamus. The primary olfactory cortex is necessary for making fine distinctions among odors and using those distinctions to consciously control behavior.

What you perceive is an active construction of reality. Perception results from the interaction of many neuron systems, each performing a simple task. Natural selection favors a perceptual system that is very efficient at picking up information needed for survival in a
three-dimensional world in which there are predators, prey, competitors, and limited resources. According to the nativist direct-perception theory of James Gibson, inborn brain mechanisms enable even babies to create perceptions directly from information supplied by the sense organs. For visual perception, your visual cortex transmits information to association areas of your parietal and temporal lobes that integrate all the pieces of information to make an image you recognize. Your brain looks for constancies and simplicity, making a huge number of perceptual decisions, often without your conscious awareness, in essentially two different ways of processing. The particular stimuli you select to process greatly affect your perceptions.

Attention is the set of processes by which you choose from among the various stimuli bombarding your senses at any instant, allowing some to be further processed by your senses and brain. You focus your awareness on only a limited aspect of all you are capable of experiencing, which is
selective attention
. In data-driven
bottom-up processing
, your sensory receptors detect external stimulation and send these raw data to the brain for analysis. Hubel and Weisel’s feature-detector theory assumes that you construct perceptions of stimuli from activity in neurons of the brain that are sensitive to specific features of those stimuli, such as lines, angles, even a letter or face. In his constructionist theory, Hermann von Helmholtz maintained that we learn through experience to convert sensations into accurate perceptions. Anne Treisman’s feature-integration theory proposes that detection of individual features of stimuli and integration into a whole occur sequentially in two different stages. First, detection of features involves bottom-up parallel processing; and second, integration of features involves less automatic, partially top-down serial processing. Concept-driven
top-down processing
takes what you already know about particular stimulation, what you remember about the context in which it usually appears, and how you label and classify it, to give meaning to your perceptions. Your expectations, previous experiences, interests, and biases give rise to different perceptions. Where you perceive a conflict among senses, vision usually dominates, which is called
visual capture
. That accounts for why you think the voice is coming from a ventriloquist’s wooden pal when the puppet’s mouth moves.

Max Wertheimer, Kurt Koffka, and Wolfgang Kohler studied how the mind organizes sensations into perceptions of meaningful patterns or forms, called a
gestalt
in German. These Gestalt psychologists concluded that in perception, the whole is different from, and can be greater than, the sum of its parts. Unlike structuralists of the early 1900s, they thought that forms are perceived not as combinations of features, but as wholes.

This is exemplified by the
phi phenomenon
, which is the illusion of movement created by presenting visual stimuli in rapid succession. Videos consist of slightly different frames projected rapidly one after another, giving the illusion of movement. Gestaltists also noted that we see objects as distinct from their surroundings. The figure is the dominant object, and the ground is the natural and formless setting for the figure. This is called the figure–ground relationship. Gestaltists claimed that the nervous system is innately predisposed to respond to patterns of stimuli according to rules or principles. Their most general principle was the law of Pragnanz, or good form, which claimed that we tend to organize patterns in the simplest way possible. Other principles of organization include proximity, closure, similarity and continuity or continuation. Consider the following: DEMON DAY BREAK FAST. Looking at the groups of letters, you probably read the four words demon, day, break, and fast, rather than Monday, daybreak, or breakfast. Proximity, the nearness of objects to each other, is an organizing principle. We perceive objects that are close together as parts of the same pattern. Do you know someone who writes letters without
quite closing the letter “o” or crossing the “t”? You probably still know what the letter is. The principle of closure states that we tend to fill in gaps in patterns. The closure principle is not limited to vision. For example, if someone started singing, “Happy Birthday to . . . ,” you might finish it in your mind. The principle of similarity states that like stimuli tend to be perceived as parts of the same pattern. The principle of continuity or continuation states that we tend to group stimuli into forms that follow continuous lines or patterns.

Optical
or
visual illusions
are discrepancies between the appearance of a visual stimulus and its physical reality. Visual illusions, such as reversible figures, illustrate the mind’s tendency to separate figure and ground in the absence of sufficient cues for deciding which is which. Illusory contours illustrate the tendency of the perceptual system to fill in missing elements to perceive whole patterns.

Survival in a three-dimensional world requires adaptations for determining the distances of objects around you.
Depth perception
is the ability to judge the distance of objects. You interpret visual cues that tell you how near or far away objects are. Cues are either monocular or binocular.
Monocular cues
are clues about distance based on the image of one eye, whereas
binocular cues
are clues about distance requiring two eyes.