Apply principles of habituation, dishabituation, and sensitization to real-life scenarios
Identify the conditioned stimulus, unconditioned stimulus, conditioned response, and unconditioned response in a Pavlovian learning paradigm
Distinguish between negative reinforcement, positive reinforcement, negative punishment, and positive punishment
Predict how reinforcement schedule will affect relative frequency of behavioral response in an operant conditioning scenario:
To a psychologist, learning refers specifically to the way in which we acquire new behaviors. To understand learning,
we must start with the concept of a stimulus.
A stimulus can be defined as anything to which an organism can respond, including all
of the sensory inputs we discussed in Chapter 2 of MCAT Behavioral Sciences Review. The combination of stimuli and responses serves as the basis for all behavioral learning.
Responses to stimuli can change over time depending on the frequency and intensity
of the stimulus. For instance, repeated exposure to the same stimulus can cause a
decrease in response called habituation. This is seen in many first-year medical students: students often have an intense
physical reaction the first time they see a cadaver or treat a severe laceration,
but as they get used to these stimuli, the reaction lessens until they are unbothered
by these sights.
The opposite process can also occur. Dishabituation is defined as the recovery of a response to a stimulus after habituation has occurred.
Dishabituation is often noted when, late in the habituation of a stimulus, a second
stimulus is presented. The second stimulus interrupts the habituation process and
thereby causes an increase in response to the original stimulus. Imagine, for example,
that you’re taking a long car trip and driving for many miles on a highway. After
a while, your brain will get used to the sights, sounds, and sensations of highway
driving: the dashed lines dividing the lanes, the sound of the engine and the tires
on the road, and so on. Habituation has occurred. At some point you use an exit ramp,
and these sensations change. As you merge onto the new highway, you pay more attention
to the sensory stimuli coming in. Even if the stimuli are more or less the same as
on the previous highway, the presentation of a different stimulus (using the exit
ramp) causes dishabituation and a new awareness of—and response to—these stimuli.
Dishabituation is temporary and always refers to changes in response to the original
stimulus, not the new one.
Key Concept
Dishabituation is the recovery of a response to a stimulus, usually after a different
stimulus has been presented. Note that the term refers to changes in response to the
original stimulus, not the new one.
Learning, then, is a change in behavior that occurs in response to a stimulus. While
there are many types of learning, the MCAT focuses on two types: associative learning
and observational learning.
Associative Learning
Associative learning is the creation of a pairing, or association, either between two stimuli or between
a behavior and a response. On the MCAT, you’ll be tested on two kinds of associative learning:
classical and operant conditioning.
Classical Conditioning
Classical conditioning is a type of associative learning that takes advantage of biological, instinctual
responses to create associations between two unrelated stimuli. For many people, the
first name that comes to mind for research in classical conditioning is Ivan Pavlov.
His experiments on dogs were not only revolutionary, but also provide a template for
the way the MCAT will test classical conditioning.
Classical conditioning works, first and foremost, because some stimuli cause an innate
or reflexive physiological response. For example, we reflexively salivate when we
smell bread baking in an oven, or we may jump or recoil when we hear a loud noise.
Any stimulus that brings about such a reflexive response is called an unconditioned stimulus, and the innate or reflexive response is called an unconditioned response. Many stimuli do not produce a reflexive response and are known as neutral stimuli.
Neutral stimuli can be referred to as signaling stimuli if they have the potential to be used as a conditioning stimulus.
In Pavlov’s experiment, the unconditioned stimulus was meat, which would cause the
dogs to salivate reflexively, and the neutral stimulus was a ringing bell. Through
the course of the experiment, Pavlov repeatedly rang the bell before placing meat
in the dogs’ mouths. Initially, the dogs did not react much when they only heard the
bell ring without receiving meat. However, after this procedure was repeated several
times, the dogs began to salivate when they heard the bell ring. In fact, the dogs
would salivate even if Pavlov only rang the bell and did not deliver any meat. Pavlov
thereby turned a neutral stimulus into a conditioned stimulus: a normally neutral stimulus that, through association, now causes a reflexive response
called a conditioned response. Classical conditioning, then, is the process of taking advantage of a reflexive,
unconditioned stimulus to turn a neutral stimulus into a conditioned stimulus, as
shown in Figure 3.1. This process is also referred to as acquisition.
Notice that the stimuli change in this experiment, but the response is the same throughout.
Because salivation in response to food is natural and requires no conditioning, it
is an unconditioned response in this context. On the other hand, when paired with
a conditioned stimulus, salivation is considered a conditioned response.
MCAT Expertise
On the MCAT, the key to telling conditioned and unconditioned responses apart will
be to look at which stimulus is causing them: unconditioned stimuli cause an unconditioned
response, while conditioned stimuli cause a conditioned response.
Just because a conditioned response has been acquired does not mean that it is permanent.
If the conditioned stimulus is presented without the unconditioned stimulus enough
times, the organism can become habituated to the conditioned stimulus and extinction occurs. If the bell rings often enough without the dog getting meat, the dog may
stop salivating when the bell sounds. Interestingly, even this extinction of a response
is not always permanent; after some time, if an extinct conditioned stimulus is presented
again, a weak conditioned response can sometimes be exhibited, a phenomenon called
spontaneous recovery.
There are a few processes that can modify the response to a conditioned stimulus after
acquisition has occurred. Generalization is a broadening effect by which a stimulus similar enough to the conditioned stimulus
can also produce the conditioned response. In one famous experiment, researchers conditioned
a child called Little Albert to be afraid of a white rat by pairing the presentation
of the rat with a loud noise. Subsequent tests showed that Little Albert’s conditioning
had generalized such that he also exhibited a fear response to a white stuffed rabbit,
a white sealskin coat, and even a man with a white beard.
Finally, in discrimination, an organism learns to distinguish between two similar stimuli. This is the opposite
of generalization. Pavlov’s dogs could have been conditioned to discriminate between
bells of different tones by having one tone paired with meat, and another presented
without meat. In this case, association could have occurred with one tone but not
the other.
MCAT Expertise
Classical conditioning is a favorite topic on the MCAT. Expect at least one question
to describe a Pavlovian experiment and ask you to identify the role of one of the
stimuli or responses described.
Operant Conditioning
Whereas classical conditioning is concerned with instincts and biological responses,
operant conditioning links voluntary behaviors with consequences in an effort to alter the frequency of
those behaviors. Just as the MCAT will test you on the difference between conditioned
and unconditioned responses and stimuli, it will ask you to distinguish between reinforcement
and punishment too. Operant conditioning is associated with B. F. Skinner, who is
considered the father of behaviorism, the theory that all behaviors are conditioned. The four possible relationships between
stimulus and behavior are summarized in Figure 3.2.
Figure3.2.Terminology of Operant Conditioning
Reinforcement
Reinforcement is the process of increasing the likelihood that an individual will perform a behavior.
Reinforcers are divided into two categories. Positive reinforcers increase a behavior by adding a positive consequence or incentive following the desired
behavior. Money is an example of a common and strong positive reinforcer: employees
will continue to work if they are paid. Negative reinforcers act similarly in that they increase the frequency of a behavior, but they do so by
removing something unpleasant. For example, taking an aspirin reduces a headache,
so the next time you have a headache, you are more likely to take one. Negative reinforcement
is often confused with punishment, which will be discussed in the next section, but
remember that the frequency of the behavior is the distinguishing factor: any reinforcement—positive
or negative—increases the likelihood that a behavior will be performed.
Real World
This concept of learning by consequence forms the foundation for behavioral therapies
for many disorders including phobias, anxiety disorders, and obsessive–compulsive
disorder.
Negative reinforcers can be subdivided into escape learning and avoidance learning,
which differ in the timing of the unpleasant stimulus. Taking aspirin is an example
of escape learning: the role of the behavior is to reduce the unpleasantness of something that already
exists, like a headache. Avoidance learning, on the other hand, is meant to prevent the unpleasantness of something that has
yet to happen. In fact, you are practicing avoidance right now: you are studying to
avoid the unpleasant consequence of a poor score on the MCAT. When you do well on
Test Day, that success will positively reinforce the behavior of studying for the
next major exam of your medical career: the United States Medical Licensing Examination®
(USMLE®)!
Classical and operant conditioning can be used hand-in-hand. For example, dolphin
trainers take advantage of reinforcers when training dolphins to perform tricks. Sometimes,
the trainers will feed the dolphin a fish after it performs a trick. The fish can
be said to be a primary reinforcer because the fish is a treat that the dolphin responds to naturally. Dolphin trainers
also use tiny handheld devices that emit a clicking sound. This clicker would not
normally be a reinforcer on its own, but the trainers use classical conditioning to
pair the clicker with fish to elicit the same response. The clicker is thus a conditioned reinforcer, which is sometimes called a secondary reinforcer. Eventually, the dolphin may even associate the presence of the trainer with the possibility of reward, making the presence of the trainer a discriminative stimulus. A discriminative stimulus indicates that reward is potentially available in an operant conditioning paradigm.
Punishment
In contrast to reinforcement, punishment uses conditioning to reduce the occurrence of a behavior. Positive punishment adds an unpleasant consequence in response to a behavior to reduce that behavior;
for example, in some countries a thief may
be flogged for stealing, which is intended to stop him from stealing again. Negative punishment is the reduction of a behavior when a stimulus is removed. For example, a parent
may forbid her child from watching television as a consequence for bad behavior, with
the goal of preventing the behavior from happening again.
Key Concept
Negative reinforcement is often confused with positive punishment. Negative reinforcement
is the removal of a bothersome stimulus to encourage a behavior; positive punishment is the addition of a bothersome stimulus to reduce a behavior.
Reinforcement Schedules
The presence or absence of reinforcing or punishing stimuli is just a part of the
story. The rate at which desired behaviors are acquired is also affected by the schedule
being used to affect those behaviors. Reinforcement schedules have two different factors:
whether the schedule is fixed or variable, and whether the schedule is based on a
ratio or an interval.
Fixed-ratio (FR) schedules reinforce a behavior after a specific number of performances of that behavior. For
example, in a typical operant conditioning experiment, researchers might reward a
rat with a food pellet every third time it presses a bar in its cage. Continuous reinforcement is a fixed-ratio schedule in which the behavior is rewarded every time it is performed.
Variable-ratio (VR) schedules reinforce a behavior after a varying number of performances of the behavior, but
such that the average number of performances to receive a reward is relatively constant.
With this type of reinforcement schedule, researchers might reward a rat first after
two button presses, then eight, then four, then finally six.
Fixed-interval (FI) schedules reinforce the first instance of a behavior after a specified time period has elapsed.
For example, once our rat gets a pellet, it has to wait 60 seconds before it can get
another pellet. The first lever press after 60 seconds gets a pellet, but subsequent
presses during those 60 seconds accomplish nothing.
Variable-interval (VI) schedules reinforce a behavior the first time that behavior is performed after a varying interval
of time. Instead of waiting exactly 60 seconds, for example, our rat might have to
wait 90 seconds, then 30 seconds, then three minutes. In each case, once the interval
elapses, the next press gets the rat a pellet.
Of these schedules, variable-ratio works the fastest for learning a new behavior,
and is also the most resistant to extinction. The effectiveness of the various reinforcement
schedules is demonstrated in Figure 3.3.
Figure3.3.Reinforcement SchedulesHatches correspond to instances of reinforcement. The start of each line corresponds
to time zero for that schedule.
There are a few things to note in this graph. First, variable-ratio schedules have
the fastest response rate: the rat will continue pressing the bar quickly with the
hope that the next press will be the “right one.” Also note that fixed schedules (fixed-ratio
and fixed-interval) often have a brief moment of no responses after the behavior is
reinforced: the rat will stop hitting the lever until it wants another pellet, once
it has figured out what behavior is necessary to receive the pellet.
Mnemonic
VR stands for Variable-Ratio, but it can also stand for Very Rapid and Very Resistant to extinction.
Real World
Gambling (and gambling addiction) is so difficult to extinguish because most gambling
games are based on variable-ratio schedules. While the probability of winning the
jackpot on any individual pull of a slot machine is the same, we get caught in the
idea that the next pull will be the “right one.”
One final idea associated with operant conditioning is the concept of shaping. Shaping is the process of rewarding increasingly specific behaviors. For example, if you
wanted to train a bird to spin around in place and then peck a key on a keyboard,
you might first give the bird a treat for turning slightly to the left, then only
for turning a full 90 degrees, then 180, and so on. Then you might only reward this
behavior if done near the keyboard until eventually the bird is only rewarded once
the full set of behaviors is performed. While it may take some time, the use of shaping
in operant conditioning can allow for the training of extremely complicated behaviors.
Cognitive and Biological Factors in Associative Learning
It would be incorrect to say that classical and operant conditioning are the only
factors that affect behavior, nor would it be correct to say that we are all mindless
and robotic, unable to resist the rewards and punishments that occur in our lives.
Since Skinner’s initial perspectives, it has been found that many cognitive and biological
factors are at work that can change the effects of associative learning or allow us
to resist them altogether.
Many organisms undergo latent learning, which is learning that occurs without a reward but that is spontaneously demonstrated
once a reward is introduced. The classic experiment associated with latent learning
involves rats running a maze. Rats that were simply carried through the maze and then
incentivized with a food reward for completing the maze on their own performed just
as well—and in some cases better—than those rats that had been trained to run the
maze using more standard operant conditioning techniques by which they were rewarded
along the way.
Problem solving
is another method of learning that steps outside the standard behaviorist approach.
Think of the way young children put together a jigsaw puzzle: often, they will take
pieces one-by-one and try to make them fit together until they find the correct match.
Many animals will also use this kind of trial-and-error approach, testing behaviors
until they yield a reward. As we get older, we gain the ability to analyze the situation
and respond correctly the first time, as when we seek out the correct puzzle piece
and orientation based on the picture we are forming. Humans and chimpanzees alike
will often avoid trial-and-error learning and instead take a step back, observe the
situation, and take decisive action to solve the challenges they face.
Not all behaviors can be taught using operant conditioning techniques. Many animals
are predisposed to learn (or not learn) behaviors based on their own natural abilities
and instincts. Animals are most able to learn behaviors that coincide with their natural
behaviors: birds naturally peck when searching for food, so rewarding them with food
in response to a pecking-based behavior works well. This predisposition is known as
preparedness. Similarly, it can be very difficult to teach animals behaviors that work against
their natural instincts. For example, researchers used behavioral techniques to try
to train raccoons to place coins in a piggy bank. Their efforts were unsuccessful,
as the raccoons would pick up the coins, rub them together, and dip them into the
bank before pulling them back out. The researchers concluded that the task they were
trying to train the raccoons to perform was conflicting with their natural food-gathering
instinct, which was to rub seeds together and wash them in a stream to clean them
before eating. This difficulty in overcoming instinctual behaviors is called instinctive drift. The researchers had far better luck training the raccoons to place a ball in a basketball
net, as the ball was too large to trigger the food-washing instinct.
Observational Learning
Observational learning is the process of learning a new behavior or gaining information by watching others.
The most famous and perhaps most controversial study into observational learning is
Albert Bandura’s Bobo doll experiment, in which children watched an adult in a room
full of toys punching and kicking an inflatable clown toy. When the children were
later allowed to play in the room, many of them ignored the other toys in the room
and inflicted similar violence on the Bobo doll just as they had seen the adult do.
It’s important to note that observational learning is not simply imitation because
observational learning can be used to teach individuals to avoid behavior as well.
In later iterations of the Bobo doll experiment, children who watched the adult get
scolded after attacking the Bobo doll were less likely to be aggressive toward the
Bobo doll themselves.
Real World
The connection between violent video games and aggressive behavior is still under
active debate. While there are many interest groups on both sides of the controversy,
the American Academy of Pediatrics (a major medical society) published one report
in which they attributed a 13 to 22% increase in aggressive behavior to observational
learning from video games.
Like associative learning, there are a few neurological factors that affect observational
learning. The most important of these are mirror neurons. These neurons are located in the frontal and parietal lobes of the cerebral cortex
and fire both when an individual performs an action and when that individual observes
someone else performing that action. Mirror neurons are largely involved in motor
processes, but additionally are thought to be related to empathy and vicarious emotions;
some mirror neurons fire both when we experience an emotion and also when we observe
another experiencing the same emotion. Mirror neurons also play a role in imitative
learning by a number of primates, as shown in Figure 3.4.
Figure3.4.Use of Mirror Neurons in a MacaqueMany neonatal primates imitate facial expressions using mirror neurons.
Research suggests that observational learning through modeling is an important factor in determining an individual’s behavior throughout his or
her lifetime. People learn what behaviors are acceptable by watching others perform
them. Much attention is focused on violent media or domestic abuse as models for antisocial
behavior, but prosocial modeling can be just as powerful. Of course, observational
learning is strongest when a model’s words are consistent with his or her actions.
Many parents adopt a Do as I say, not as I do approach when teaching their children, but research suggests that children will disproportionately
imitate what the model did, rather than what the model said.
