Classical conditioning
Classical conditioning is a behavioral procedure in which a biologically potent stimulus is paired with a neutral stimulus. The term classical conditioning refers to the process of an automatic, conditioned response that is paired with a specific stimulus. It is essentially equivalent to a signal.
Ivan Pavlov, the Russian physiologist, studied classical conditioning with detailed experiments with dogs, and published the experimental results in 1897. In the study of digestion, Pavlov observed that the experimental dogs salivated when fed red meat. Pavlovian conditioning is distinct from operant conditioning, through which the strength of a voluntary behavior is modified, either by reinforcement or by punishment. However, classical conditioning can affect operant conditioning; classically conditioned stimuli can reinforce operant responses.
Classical conditioning is a basic behavioral mechanism, and its neural substrates are now beginning to be understood. Though it is sometimes hard to distinguish classical conditioning from other forms of associative learning ; a number of observations differentiate them, especially the contingencies whereby learning occurs.
Together with operant conditioning, classical conditioning became the foundation of behaviorism, a school of psychology which was dominant in the mid-20th century and is still an important influence on the practice of psychological therapy and the study of animal behavior. Classical conditioning has been applied in other areas as well. For example, it may affect the body's response to psychoactive drugs, the regulation of hunger, research on the neural basis of learning and memory, and in certain social phenomena such as the false consensus effect.
Definition
Classical conditioning occurs when a conditioned stimulus is paired with an unconditioned stimulus. Usually, the conditioned stimulus is a neutral stimulus, the unconditioned stimulus is biologically potent and the unconditioned response to the unconditioned stimulus is an innate reflex response. After pairing is repeated, the organism exhibits a conditioned response to the conditioned stimulus when the conditioned stimulus is presented alone. Thus, unlike the UR, the CR is acquired through experience, and it is also less permanent than the UR.Usually the conditioned response is similar to the unconditioned response, but sometimes it is quite different. For this and other reasons, most learning theorists suggest that the conditioned stimulus comes to signal or predict the unconditioned stimulus, and go on to analyse the consequences of this signal. Robert A. Rescorla provided a clear summary of this change in thinking, and its implications, in his 1988 article "Pavlovian conditioning: It's not what you think it is". Despite its widespread acceptance, Rescorla's theory also has shortcomings.
A false-positive involving classical conditioning from chance has been proven to be improbable in successfully conditioning a response. The element of contingency has been further tested and is said to have "outlived any usefulness in the analysis of conditioning."
Classical conditioning differs from operant or instrumental conditioning: in classical conditioning, behaviors are modified through the association of stimuli as described above, whereas in operant conditioning behaviors are modified by the effect they produce.
Evaluative conditioning
Evaluative conditioning is a form of classical conditioning, in that it involves a change in the responses to the conditioned stimulus that results from pairing the conditioned stimulus with an unconditioned stimulus. Whereas classic conditioning can refer to a change in any type of response, evaluative conditioning concerns only a change in the evaluative responses to the conditioned stimulus, that is, a change in the liking of the conditioned stimulus. Evaluative conditioning is defined as a change in the association of a stimulus that is due to the pairing of that stimulus with another positive or negative stimulus. The first stimulus is often referred to as the conditioned stimulus and the second stimulus as the unconditioned stimulus. A conditioned stimulus becomes more positive when it has been paired with a positive unconditioned stimulus and more negative when it has been paired with a negative unconditioned stimulus. Evaluative conditioning thus refers to attitude formation or change toward an object due to that object's mere co-occurrence with another object.A classic example of the formation of attitudes through conditioning is the 1958 experiment by Staats and Staats. Subjects first were asked to learn a list of words that were presented visually, and were tested on their learning of the list. They then did the same with a list of words presented orally, all of which set the stage for the critical phase of the experiment which was portrayed as an assessment of subjects' ability to learn via both visual and auditory channels at once. During this phase, subjects were exposed visually to a set of nationality names, specifically Dutch and Swedish. Approximately one second after the nationality appeared on the screen, the experimenter announced a word aloud. Most of these latter words, none of which were repeated, were neutral. Included, however, were a few positive words and a few negative words. These words were systematically paired with the two conditional stimuli nationalities such that one always appeared with positive words and the other with negative words. Thus, the conditioning trials were embedded within a stream of visually presented nationality names and orally presented words. When the conditioning phase was completed, the subjects were first asked to recall the words that had been presented visually and then to evaluate them, presumably because how they felt about those words might have affected their learning. The conditioning was successful. The nationality that had been paired with the more positive unconditional stimuli was rated as more pleasant than the one paired with the negative unconditional stimuli.
Procedures
Pavlov's research
The best-known and most thorough early work on classical conditioning was done by Ivan Pavlov, although Edwin Twitmyer published some related findings a year earlier. During his research on the physiology of digestion in dogs, Pavlov developed a procedure that enabled him to study the digestive processes of animals over long periods of time. He redirected the animals' digestive fluids outside the body, where they could be measured.Pavlov noticed that his dogs began to salivate in the presence of the technician who normally fed them, rather than simply salivating in the presence of food. Pavlov called the dogs' anticipatory salivation "psychic secretion". Putting these informal observations to an experimental test, Pavlov presented a stimulus and then gave the dog food; after a few repetitions, the dogs started to salivate in response to the stimulus. Pavlov concluded that if a particular stimulus in the dog's surroundings was present when the dog was given food then that stimulus could become associated with food and cause salivation on its own.
Terminology
In Pavlov's experiments the unconditioned stimulus was the food because its effects did not depend on previous experience. The metronome's sound is originally a neutral stimulus because it does not elicit salivation in the dogs. After conditioning, the metronome's sound becomes the conditioned stimulus or conditional stimulus; because its effects depend on its association with food. Likewise, the responses of the dog follow the same conditioned-versus-unconditioned arrangement. The conditioned response is the response to the conditioned stimulus, whereas the unconditioned response corresponds to the unconditioned stimulus.Pavlov reported many basic facts about conditioning; for example, he found that learning occurred most rapidly when the interval between the CS and the appearance of the US was relatively short.
As noted earlier, it is often thought that the conditioned response is a replica of the unconditioned response, but Pavlov noted that saliva produced by the CS differs in composition from that produced by the US. In fact, the CR may be any new response to the previously neutral CS that can be clearly linked to experience with the conditional relationship of CS and US. It was also thought that repeated pairings are necessary for conditioning to emerge, but many CRs can be learned with a single trial, especially in fear conditioning and taste aversion learning.
Image:delay,trace conditioning.svg|thumb|right|384px|Diagram representing forward conditioning. The time interval increases from left to right.
Forward conditioning
Learning is fastest in forward conditioning. During forward conditioning, the onset of the CS precedes the onset of the US in order to signal that the US will follow. Two common forms of forward conditioning are delay and trace conditioning.- Delay conditioning: In delay conditioning, the CS is presented and is overlapped by the presentation of the US. For example, if a person hears a buzzer for five seconds, during which time air is puffed into their eye, the person will blink. After several pairings of the buzzer and the puff, the person will blink at the sound of the buzzer alone. This is delay conditioning.
- Trace conditioning: During trace conditioning, the CS and US do not overlap. Instead, the CS begins and ends before the US is presented. The stimulus-free period is called the trace interval or the conditioning interval. If in the above buzzer example, the puff came a second after the sound of the buzzer stopped, that would be trace conditioning, with a trace or conditioning interval of one second.
Simultaneous conditioning