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months, never to return. Why are we humans less equipped with inborn, reflexlike
rituals than the stickleback? Because we adapt to life’s demands not by instinct but
through learning.
Description
Figure 5.1 Stickleback Models
Republished with permission of Oxford Unviersity Press, from The
Study of Instinct. N. Tinbergen. New York:1951; permission conveyed
through Copyright Clearance Center, Inc.
Habituation
When psychologists talk about learning, they are referring to a relatively
permanent change in knowledge or behavior that comes about as a result of
experience. Experience is necessary for us to speak, read, write, add and subtract,
ride a bicycle, swim, play a saxophone or trumpet, or know how to charm a romantic
partner. The topic of learning is near and dear to the hearts of all psychologists—
regardless of whether they study biological, cognitive, developmental, social, or
clinical processes. Often what we learn makes us happier, healthier, and more
successful; sometimes it does not. The beauty of adaptation by learning is that it is
flexible, not rigidly preset like a stickleback’s dance-and-attack ritual. In principle, this
means that each of us can learn to behave in ways that benefit rather than harm
ourselves and others. The question is: How does this learning take place?
learning. A relatively permanent change in knowledge or behavior that results
from experience.
The simplest form of learning is habituation—a tendency to become familiar with
a stimulus merely as a result of repeated exposure. The first time it happens, a
sudden loud noise or a blast of cold air has a startling effect on us and triggers an
“orienting reflex.” Among humans, the eyes widen, the eyebrows rise, muscles
tighten, the heart beats faster, skin resistance drops, and brain-wave patterns
indicate a heightened level of physiological arousal (Sokolov, 1963). On the second
and third exposures to the stimulus, the effect is weakened. Then as we become
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acclimated or “habituated” to the stimulus, the novelty wears off, the startle reaction
disappears, and boredom sets in.
habituation. The tendency of an organism to become familiar with a stimulus as a
result of repeated exposure.
Habituation is a primitive form of learning and is found among mammals, birds,
fish, insects, and all other organisms. For example, sea snails reflexively withdraw
their gills at the slightest touch. Then after repeated tactile stimulation, the response
disappears (Kandel, 1979). Animals may also habituate to objects that naturally
evoke fear after repeated and harmless exposure. When lab rats were presented with
a cat collar smeared with a cat’s odor, they ran from it and hid. Figure 5.2, however,
shows that after several presentations the rats hid for decreasing amounts of time,
eventually resembling control group rats exposed to an odorless collar (Dielenberg &
McGregor, 1999).
Description
Figure 5.2 Habituation of Fear
Adapted from Dielenberg, R. A., & McGregor, I. S. (1999). Habituation
of the hiding response to cat odor in rats (Rattus norvegicus). Journal of
Comparative Psychology, 113(4), 376–387. https://doi.org/10.1037/0735-
7036.113.4.376
Habituation also occurs in human infants (Leader, 2016). In one classic study, for
example, if a picture or sound is presented over and over again, an infant will
eventually get bored, lose interest, look away, and exhibit a lower heart rate
(Bornstein, 1989). Think about everyday life, and numerous examples of habituation
will come to mind. People who move from a large city to the country or from a region
of the world that is hot to one that is cold often need time to adjust to the sudden
change in stimulation. Once they do, the new environment seems less noisy, quiet,
hot, or cold. In a series of experiments, adults were subliminally exposed to words
that arouse emotional reactions that are extremely positive (free, beach, baby) and
negative (cancer, war, hell). Later, they rated these same words as less positive and
negative than they did other, equally extreme, words that were not previously
presented (Dijksterhuis & Smith, 2002). Habituation also has important implications
for the power of rewards to motivate us. Regardless of whether the rewarding
stimulus is food, water, or an opportunity to explore a new environment, it tends to
lose impact, at least temporarily, with repeated use (Domjan, 2018a; McSweeney &
Swindell, 1999).
In habituation, an organism learns from exposure that a certain stimulus is
familiar. Over the years, however, psychologists have focused more on the ways in
which we learn relationships between events. In this chapter, three such processes
are discussed: classical conditioning, operant conditioning, and observational
learning.
CLASSICAL CONDITIONING
LEARNING OBJECTIVES
Explain what Pavlov learned from his experiments with salivating dogs.
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Describe how Pavlov’s work on classical conditioning influenced how we
understand learning.
Describe how classical conditioning works and its relevance to human
behavior.
Discuss whether it is possible to condition new fears or preferences and
whether bodily functions can be conditioned similarly.
There are certainly moments in your life that stand out, ones that you will always
remember. Maybe it was your first kiss, the championship game you won, or even a
moment as simple as your first day of college—meeting your classmates and feeling
like an adult, ready to earn a degree and achieve your goals. To this day, these
memories may flood to your mind in certain settings.
In stark contrast, the moments in our lives are not always pleasant. It could be
something as simple as the first time you were pulled over for a minor traffic violation,
or it could be something more serious, such as a car accident—as you vividly recall
the red lights flashing on the dashboard, the smell of burned rubber, and the blast of
cold air that hit your face when you climbed out through the door. Parts of the
incident, such as the song playing in the car, may come to memory at other times.
For years, you might flinch whenever you hear it.
Following Aristotle, modern philosophers and psychologists have long believed
that the key to learning is association, a tendency to connect events that occur
together in space or time. Can learning by association be studied in a scientific
manner? Yes. In fact, many theories of associative learning have been proposed and
tested over the years (Pearce & Bouton, 2001). With the arrival of the 20th century,
psychology was poised and ready for one of its most important discoveries.
Ivan Pavlov and some of the 200 other scientists and a dog who worked with him
during his illustrious career.
Bettmann / Contributor/Getty
Pavlov’s Discovery
Enter Ivan Pavlov, a Russian physiologist. After receiving his medical degree in
1882, he spent 20 years studying the digestive system and won a Nobel Prize for that
research in 1904. Pavlov was the complete dedicated scientist. Rumor has it that he
once reprimanded a lab assistant who was 10 minutes late for an experiment
because of street riots stemming from the Russian Revolution: “Next time there’s a
revolution,” he said, “get up earlier!” (Hothersall, 1990).
Ironically, Pavlov’s most important contribution was the result of an incidental
discovery. In studying the digestive system, he strapped dogs in a harness, placed
different types of food in their mouths, and measured the flow of saliva through a tube
surgically inserted in the cheek (illustrated in Figure 5.3). But there was a “problem”:
After repeated sessions, the dogs would begin to salivate before the food was put in
their mouths. In fact, they would drool at the mere sight of food, the dish it was placed
in, the assistant who brought it, or even the sound of the assistant’s approaching
footsteps. Pavlov saw these “psychic secretions” as a nuisance, so he tried to
eliminate the problem by sneaking up on the dogs without warning. He soon realized,
however, that he had stumbled on a very basic form of learning. This phenomenon
was classical conditioning, and Pavlov devoted the rest of his life to studying it.
classical conditioning. A type of learning in which an organism comes to
associate one stimulus with another (also called Pavlovian conditioning).
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Description
Figure 5.3 Pavlov’s Classical-Conditioning Apparatus
Science Source
To examine the classical conditioning systematically, Pavlov needed to control the
delivery of food, often a dry meat powder, as well as the events that preceded it. The
animals did not have to be trained or “conditioned” to salivate. The salivary reflex is
an innate unconditioned response (UR) that is naturally set off by food in the
mouth, an unconditioned stimulus (US). There are numerous unconditioned
stimulus-response connections. Tap your knee with a rubber mallet (US) and your leg
will jerk (UR). Blow a puff of air into your eye (US) and you’ll blink (UR). Turn the
volume up on an alarm clock (US) and, when it rings, your muscles will tighten (UR).
In each case, the US automatically elicits the UR. No experience is necessary—just a
reflex.
unconditioned response (UR). An unlearned response (salivation) to an
unconditioned stimulus (food).
unconditioned stimulus (US). A stimulus (food) that triggers an unconditioned
response (salivation).
Using the salivary reflex as a starting point, Pavlov (1927) sought to determine
whether dogs could be trained by association to respond to a “neutral” stimulus—one
that does not naturally elicit a response. To find out, he conducted a series of
experiments in which he repeatedly paired noises—such as the clicking of a
metronome or the ringing of a bell—before placing food in the dog’s mouth. Bell, food.
Bell, food. After a series of these paired events, the dog started to salivate to the
sound alone. Because the bell, which was initially a neutral stimulus, came to elicit
the response through its association with food, it became a conditioned stimulus
(CS), and salivation, a conditioned response (CR). With his initial experiment as a
model, Pavlov and others trained dogs to salivate in response to a range of stimuli,
not just noises. Odors, lights, colored objects, and a touch on the leg also elicited the
salivation response.
conditioned stimulus (CS). A neutral stimulus (bell) that comes to evoke a
classically conditioned response (salivation).
conditioned response (CR). A learned response (salivation) to a classically
conditioned stimulus (bell).
Following the basic classical-conditioning procedure diagrammed in Figure 5.4,
researchers have trained animals to react to a host of neutral stimuli that have been
paired with an unpleasant or pleasant US. In one study, rats froze and did not move
whenever they were put into a cage in which they had previously been exposed to
high concentrations of carbon dioxide (Mongeluzi, Rosellini, Caldarone, Stock, &
Abrahamson, 1996). In a second study, male quails became sexually aroused when
they were placed into a chamber in which they had previously copulated with female
birds (Domjan, Blesbois, & Williams, 1998). In a third study, human couples had a
neutral odor paired with a sexual interaction (CS+) and another neutral odor paired
with nonsexual coupled interaction, such as just watching a movie (CS–). Results
showed increased genital responding to the CS+ and decreased responding to the
CS– (Hoffmann, Peterson, & Garner, 2012).
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Description
Figure 5.4 Classical Conditioning
As we’ll learn, classical conditioning affects us all in ways that we’re often not
aware of. We learn to salivate (CR) to lunch bells, menus, the smell of food cooking,
and the sight of a refrigerator (CS) because these stimuli are often followed by eating
(US). Similarly, we may cringe when seeing a needle in the doctor’s office because of
past associations between that sight and pain. And we tremble at the sight of flashing
blue and red lights in the rearview mirror because of its past association with
speeding tickets.
Basic Principles
Inspired by his initial discovery, Pavlov spent more than 30 years examining the
factors that influence classical conditioning. Other researchers throughout the world
also became involved. As a result, we now know that various species can be
conditioned to blink when they hear a click that is paired with a puff of air to the eye,
to fear colored lights that signal the onset of painful electric shocks, and to develop a
dislike for foods they ate before becoming sick to the stomach (McSweeney &
Murphy, 2014). We also know that there are four basic principles of learning:
acquisition, extinction, generalization, and discrimination.
Acquisition
Classical conditioning seldom springs full blown after a single pairing of the CS
and US. Usually, it takes some number of paired trials for the initial learning, or
acquisition, of a CR. In Pavlov’s experiments, the dogs did not salivate the first time
they heard the bell or felt a touch on their leg. As shown in the left panel of Figure
5.5, however, the CR increases rapidly over the next few pairings—until the “learning
curve” peaks and levels off.
acquisition. The formation of a learned response to a stimulus through the
presentation of an unconditioned stimulus (classical conditioning) or reinforcement
(operant conditioning).
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Description
Figure 5.5 The Rise and Fall of a Conditioned Response
The acquisition of a classically conditioned response is influenced by various
factors. The most critical are the order and timing of the presentation. In general,
conditioning is quickest when the CS (the bell) precedes the onset of the US (food)—
a procedure called forward conditioning. Ideally, the CS should precede the US by
about half a second and the two should overlap somewhat in time. When the onset of
the US is delayed, conditioning takes longer and the conditioned response is weaker.
When the CS and US are simultaneous, it takes even longer. And when the US is
presented before the CS (a procedure referred to as backward conditioning), learning
often does not occur at all.
Once a buzzer, light, or other neutral stimulus gains the power to elicit a
conditioned response, it becomes a CS—and can serve as though it were the US for
yet another neutral stimulus. In one experiment, for example, Pavlov trained a dog to
salivate to the sound of a bell, using meat powder as the US. After the CS-US link
was established, he presented a second neutral stimulus, a black square, followed by
the bell—but no food. The result: After repeated pairings, the black square on its own
elicited small amounts of salivation. Through a process of higher-order conditioning,
as shown in Figure 5.6, one CS was used to create another CS. In effect, the black
square came to signal the bell, which, in turn, signaled the appearance of food
(Rescorla, 1980).
Description
Figure 5.6 Higher-Order Conditioning
Monica Wierzbicki/Body Scientific Intl.
Extinction
In the acquisition phase of classical conditioning, a CR is elicited by a neutral
stimulus that is paired with a US. But what happens to the CR when the US is
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removed? Would a dog continue to salivate to a bell if the bell is no longer followed
by food? Would the screeching dentist’s drill continue to send chills up the spine if it is
no longer followed by pain? No. If the CS is presented often enough without the US, it
eventually loses its response-eliciting power. This apparent reversal of learning is
called extinction (look again at the right side of the left panel in Figure 5.5).
extinction. The elimination of a learned response by removal of the
unconditioned stimulus (classical conditioning) or reinforcement (operant
conditioning).
Extinction is a gradual process. Pavlov found that when the same dog was
returned for testing a day or two after extinction, it again salivated to the bell—a
rebound effect known as spontaneous recovery (depicted in the middle and right
panels of Figure 5.5). Often the dogs were easily retrained after just one repairing of
the CS and US. As confirmed across multiple studies, extinction does not erase what
was initially learned during acquisition—and retraining does not erase the effects of
extinction. Rather, it appears that each learning experience suppresses, but does not
destroy, those that preceded it (Rescorla, 1996, 2001).
spontaneous recovery. The reemergence of an extinguished conditioned
response after a rest period.
Generalization
After an animal is conditioned to respond to a particular CS, other similar stimuli
will often evoke the same response. In Pavlov’s experiments, the dogs salivated not
only to the original tone but also to other tones that were similar but not identical to
the CS. Other researchers have made the same observation. In one study, for
example, rabbits were conditioned to blink to a tone of 1,200 Hz (a pitch that is
roughly two octaves higher than middle C) that was followed by a puff of air to the
eye. Later, they blinked to other tones ranging from 400 Hz to 2,000 Hz. The result:
The more similar the tone was to the CS, the more likely it was to evoke a
conditioned response. This tendency to respond to stimuli other than the original CS
is called stimulus generalization (Pearce, 1987).
stimulus generalization. The tendency to respond to a stimulus that is similar to
the conditioned stimulus.
Discrimination
Stimulus generalization can be useful because it enables us to apply what we
learn to new, similar situations. But there are drawbacks. As illustrated by the child
who is terrified of all animals because of one bad encounter with a barking dog,
generalization is not always adaptive. Sometimes we need to distinguish between
objects that are similar—a process of discrimination. Again, Pavlov was the first to
demonstrate this process. He conditioned a dog to salivate in the presence of a black
square (a CS) and then noticed that the response generalized to a gray-colored
square. Next, he conducted a series of conditioning trials in which the black square
was followed by food while the gray one was not. The result: The dog continued to
salivate only to the original CS. In a similar manner, the dog eventually learned to
discriminate between the color black and darker shades of gray.
discrimination. Behavior directed against persons because of their affiliation with
a social group.
Pavlov’s Legacy
Classical conditioning is so powerful and so basic that it occurs in animals as
primitive as the sea slug, the fruit fly, and even the flatworm (the body of the flatworm
contracts in response to electric shock; if the shock is paired repeatedly with light, the
flatworm’s body eventually contracts to the light alone) and in animals as
sophisticated as us humans (Krasne & Glanzman, 1995; Turkkan, 1989). Recently,
psychologists have taken classical conditioning in two directions: Some want to better
understand the phenomenon—how, when, and why it works—while others are eager
to apply it to different aspects of the human experience.
Theoretical Advances
Inspired by their initial success and by the Darwinian assumption that all animals
share a common evolutionary past, Pavlov and other early behaviorists made this
bold claim: Any organism can be conditioned to any stimulus. It does not matter if the
subject is a dog, cat, rat, pigeon, or person. Nor does it matter if the conditioned
stimulus is a bell, light, buzzer, or odor. Whenever an initially neutral stimulus is
paired with an unconditioned stimulus, the result is classical conditioning.
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The early behaviorists also insisted that a science of human behavior must focus
only on external, objective, quantifiable events. A stimulus can be observed and
measured. So can its effect on an overt response. Together, these form the basis for
what is known as S-R psychology. As far as the organism itself is concerned—its
instincts, drives, perceptions, thoughts, and feelings—the behaviorists would not
speculate. In fact, Pavlov was said to have fined laboratory assistants who slipped
into using “mentalistic” language. So where does the organism (O) fit in? In recent
years, researchers have come to appreciate some of the ways in which the O bridges
the S and R—giving rise to a more flexible S-O-R brand of behaviorism. Two factors
within the organism are particularly important: biological preparedness and cognitive
representations.
Biological Preparedness.
For survival purposes, all animals are biologically programmed by evolution to
learn some associations more easily than others. This phenomenon was first
discovered by John Garcia and Robert Koelling (1966). While studying the effects of
radiation exposure on laboratory rats, they noticed that the animals would not drink
from the plastic water bottles inside the radiation chambers. Since the radiation (US)
was causing nausea (UR), they reasoned, perhaps the rats had acquired an aversion
(CR) to the “plastic” taste of the water (CS).
In animal studies, rodents are often fed using drinking tubes, such as the one
shown here.
iStock.com/felixmizioznikov
To test this hypothesis, these investigators rigged an apparatus that worked as
follows: When a rat licked a plastic drinking tube, it tasted sweetened water, saw a
flash of light, and heard a loud clicking noise—all at the same time. The rats were
then exposed to a high dose of X-rays, which caused poisoning and nausea. The
result: The rats later came to avoid the sweetened water after radiation poisoning, but
they did not also learn to avoid the light or noise. The link between taste (CS) and
poison (US) was so easily learned that it took only one pairing—even though the rats
did not get sick until hours later (a far cry from the split-second CS-US interval that is
usually necessary). Garcia and Koelling (1966) next found that when the US was a
painful electric shock to the feet instead of X-ray poisoning, the rats continued to
drink the water, but this time they avoided the audiovisual stimuli instead. In other
words, although the rats were exposed to all stimuli, they proceeded to avoid only the
flavored water after X-ray poisoning and only the light and noise after shock. Why
was taste such a powerful CS when it was paired with poison but not with shock?
And why were light and noise conditioned to shock but not to poison? Think about
these associations for a moment, and one word will pop to mind: adaptiveness. In
nature, food is more likely to produce stomach poisoning than a pain in the foot, and
an external stimulus is more likely to cause a pain in the foot than stomach illness. If
you get sick after eating in a new restaurant, you are likely to blame your illness on
something you ate, not on the decor or the music that played. Clearly, we are
“prepared” by nature to learn some CS-US associations more easily than others.
More than this, when associated with dangerous outcomes, such as illness, we
acquire these associations quickly, with aversion learning being demonstrated
consistently in a single trial (Lin, Arthurs, & Reilly, 2017).
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People acquire taste aversions, too—often with important practical implications.
Consider, for example, an unfortunate side effect of chemotherapy treatments for
cancer. These drugs tend to cause nausea and vomiting. As a result, patients often
become conditioned to react with disgust and a loss of appetite to foods they had
eaten hours before the treatment (Bovbjerg et al., 1992). Thankfully, the principles of
classical conditioning offer a solution to this problem. When cancer patients are fed a
distinctive maple-flavored ice cream before each treatment, they acquire a taste
aversion to that ice cream—which becomes a “scapegoat” and protects the other
foods in the patient’s diet (Bernstein & Borson, 1986). Still, many cancer patients who
had undergone chemotherapy and survived report that they continue to feel
nauseous, and sometimes vomit, in response to the sights, smells, and tastes that
remind them of treatment—as much as 20 years later (Bernstein, 1985; National
Cancer Institute, 2017).
Cognitive Representations.
How or what we think about stimuli can also influence our response. Research on
the classical conditioning of fear reactions illustrates that organisms are biologically
predisposed to learn certain stimulus–response connections more than others. As
we’ll explore in Chapter 13, people all over the world share many of the same fears.
Particularly common are fears of darkness, height, snakes, and insects—relatively
harmless objects, some of which we may never encounter. Yet very few of us are as
terrified of automobiles, electrical outlets, appliances, and other objects that can be
dangerous. Why? Martin Seligman (1971) speculated that the reason for this disparity
is that humans are predisposed by evolution to be wary of stimuli and situations that
posed a threat to our prehistoric ancestors.
Not everyone agrees with this evolutionary analysis (Davey, 1995). However, it is
supported by various strands of research. When laboratory-raised rhesus monkeys
saw a wild-reared monkey of the same species exhibit fear in the presence of a toy
snake, they acquired an intense fear of snakes. But when they saw the other monkey
show fear in the presence of a toy rabbit, they did not similarly acquire a fear of
rabbits (Cook & Mineka, 1990; Mineka & Cook, 1993). Similar results are found in
humans. When people are conditioned to fear an object that is paired with electric
shock, their reaction—as measured by physiological arousal—is acquired faster and
lasts longer when the object is a snake, a spider, or an angry face than when it is a
neutral stimulus such as a flower, a house, or a happy face (McNally, 1987). This
differential response to fear-relevant objects is so basic that it occurs even when the
stimuli are presented subliminally, without awareness (Ohman & Soares, 1998).
After reviewing the research, Arne Ohman and Susan Mineka (2001) proposed
that human beings are equipped by evolution with fear modules designed to help us
defend against potentially life-threatening situations in the ecology of our distant
ancestors. According to Ohman and Mineka, these fear modules have four
characteristics: (a) They are highly selective, making us sensitive to some objects—
such as heights, thunder, and snakes—but not others; (b) they elicit fear responses
that are “automatic,” requiring very little attention, thought, or effort; (c) the responses
are hard to consciously control or avoid; and (d) the modules are controlled by neural
circuits in the amygdala and hippocampus—primitive, subcortical limbic structures
shared by all mammals (Adolphs, 2013; Maren, 2001).
Studies evaluating these fear modules indicate that humans’ responsiveness to
fear stimuli is similar across cultures (Landová et al., 2018), although cultural
differences are evident. For example, Joan Chiao and her colleagues evaluated
responsiveness in the amygdala among participants who were native Japanese in
Japan and Caucasian Americans living in the United States. They found
responsiveness was culture specific: The amygdala showed greater activation when
participants viewed fear (versus nonfear) faces of their own cultural group (Chiao et
al., 2008). Our experiences certainly play a significant role, but many studies today
are focused on how our culture influences our fears, our preferences, and possibly
our genetic evolution (Chiao & Immordino-Yang, 2013; Janovcová et al., 2019).
LEARNING CHECK
Going to the Dogs
You are one of Pavlov’s dogs. To get some delicious meat powder, you must
match each classical conditioning term in the right column with its closest example in
the left.
(Answers: 1. f; 2. e; 3. h; 4. d; 5. c; 6. g; 7. b; 8. a.)
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Practical Applications of Classical Conditioning
When Pavlov first found that he could train Russian dogs to drool to the sound of
a dinner bell, nobody cared. In fact, E. B. Twitmyer, an American graduate student,
had reported similar results at a psychology conference in 1904—the same year that
Pavlov won the Nobel Prize. At the time, Twitmyer was studying the knee-jerk reflex
in humans. Before each trial, he would ring a bell to warn subjects that a hammer
was about to strike the knee. Like Pavlov, he found that the subject’s leg would soon
twitch in response to the bell—even before the knee was hit. Was this a profound
development? You might think so, but Twitmyer’s presentation attracted little interest.
Conditioned Fears
Psychologists finally took notice of classical conditioning in 1914, when
behaviorist John Watson described Pavlov’s work to a group of American
psychologists. To demonstrate the relevance of the phenomenon to humans, Watson
and his assistant Rosalie Rayner (1920) conditioned a 9-month-old infant boy named
Albert to fear a white laboratory rat. “Little Albert” was a normal, healthy, welldeveloped infant. Like others his age, he was scared by loud noises but enjoyed
playing with furry little animals. Enter John Watson. Modeled after Pavlov’s research,
Watson presented Albert with a harmless white rat. Then just as the boy reached for
the animal, Watson made a loud, crashing sound by banging a steel bar with a
hammer, which caused the startled boy to jump and fall forward, burying his head in
the mattress he was lying on. After seven repetitions of this event, the boy was
terrified of the animal. What’s worse, his fear generalized, leading him to burst into
tears at the sight of a rabbit, a dog, a Santa Claus mask, and even a white fur coat
(illustrated in Figure 5.7).
Description
Figure 5.7 The Conditioning of Little Albert and Generalization
From an ethical standpoint, Watson and Rayner’s study was shameful. They
conditioned an innocent baby with a fear that seemed to spread like it was a
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