Saturday, October 13, 2012

Reinforcement and Extinction of Operant Behavior

Operant Behavior
Operant behavior is commonly described as intentional, free, voluntary, or willful. Examples of operant behavior include conversations with others, driving a car, taking notes, reading a book, and painting a picture. From a scientific perspective, operant behavior is lawful and may be analyzed in terms of its relationship to environmental events. Formally, responses Reinforcement and Extinction of Operant Behavior that produce a change in the environment and increase in frequency due to that change are called operants. The term operant comes from the verb to operate and refers to behavior that operates on the environment to produce consequences that in turn strengthen the behavior. The consequences of operant behavior are many and varied and occur across all sensory dimensions. When you turn on a light, dial a telephone, drive a car, or open a door, these operants result in visual clarity, conversation, reaching a destination, and entering a room. A positive reinforcer is defined as any consequence that increases the probability of the operant that produced it. For example, pretend that your car will not start, but when you jiggle the ignition key it fires right up. Based on past reinforcement, the operant—jiggling the key—is likely to be repeated the next time the car won’t start.
Operants are defined by the consequences they produce. Thus, opening the door to reach the other side is the operant, not the physical movement of manipulating the door. Operants are a class of responses that may vary in topography. Topography refers to the physical form or characteristics of the response. Consider the number of different ways you could open a door—you may turn the handle, push it with your foot, or (if your arms are full of books) ask someone to open it for you. All of these responses vary in topography and result in reaching the other side of the door. Because these responses result in the same consequence, they are members of the same operant class. Thus, the term operant refers to a class of related responses that may vary in topography but produce a common environmental consequence (Catania, 1973).

Discriminative Stimuli
Operant behavior is said to be emitted in the sense that it often occurs without an observable stimulus preceding it. This is in contrast to reflexive responses, which are elicited by a preceding stimulus. Reflexes are tied to the physiology of an organism and, under appropriate conditions, always occur when the eliciting stimulus is presented. For example, Pavlov showed that dogs automatically salivated when food was placed in their mouths. Dogs do not learn the relationship between food and salivation; this reflex is a characteristic of the species. Stimuli may also precede operant behavior. However, these events do not force the occurrence of the response that follows them. An event that precedes an operant and sets the occasion for behavior is called a discriminative stimulus, or SD (pronounced esse-dee).

Contingencies of Reinforcement
A contingency of reinforcement defines the relationship between the events that set the occasion for behavior, the operant class, and the consequences that follow this behavior. In a dark room (SD), when you flip on a light switch (R), the light usually comes on (Sr). This behavior does not guarantee that the room will light up; the bulb may be burned out or the switch may be broken. It is likely that the light will come on, but it is not certain. In behavioral terms, the probability of reinforcement is high, but it is not absolute. This probability may vary between 0 and 100%. A high probability of reinforcement for turning the switch to the “on” position will establish and maintain a high likelihood of this behavior.
Discriminative stimuli that precede behavior have an important role in the regulation of operant responses (Skinner, 1969). Signs that read OPEN, RESUME SPEED, or RESTAURANT; green traffic lights, a smile from across the room, and so on are examples of simple discriminative stimuli that may set the occasion for specific operants. These events regulate behavior because of a history of reinforcement in their presence.Asmile from across a room may set the occasion for approaching and talking to the person who smiled. This is because, in the past, people who smiled reinforced social interaction. Each of these events—the occasion, the operant, and the consequences of behavior— makes up the contingency of reinforcement. Consider the example of this three-part contingency shown in Fig. 4.1. The telephone ring is a discriminative stimulus that sets the occasion for the operant class of answering the phone. This behavior occurs because, in the past, talking to the other party reinforced the operant. The probability of response is very high in the presence of the ring, but it is not inevitable. Perhaps you are in the process of leaving for an important meeting, or you are in the bathtub.
Discriminative stimuli regulate behavior, but they do not stand alone. The consequences that follow behavior determine the probability of response in the presence of the discriminative stimulus. For example, most people show a high probability of answering the telephone when it rings. However, if the phone is faulty so that it rings but you cannot hear the other party when you answer it, the probability of answering the phone decreases as a function of no reinforcement. In other words, you stop answering a phone that does not work.

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