Understanding Psychology (10th Ed)

 REINFORCEMENT: THE CENTRAL CONCEPT 
OF OPERANT CONDITIONING 
Skinner called the process that leads the rat to continue pressing the key “reinforce-
ment.”  Reinforcement  is the process by which a stimulus increases the probability 
that a preceding behavior will be repeated. In other words, pressing the lever is more 
likely to occur again because of the stimulus of food. 
reinforcement
The process by which a 
stimulus increases the probability that 
a preceding behavior will be repeated.
FIGURE 1 
Edward L. Thorndike devised 
this puzzle box to study the process by 
which a cat learns to press a paddle to 
escape from the box and receive food. 
Do you think Thorndike’s work has 
relevance to the question of why 
humans voluntarily solve puzzles, such 
as crossword puzzles and jigsaw 
puzzles? Do they receive any rewards?
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Module 18 
Operant Conditioning 
185
In a situation such as this one, the food is called a reinforcer. A  reinforcer  is any 
stimulus that increases the probability that a preceding behavior will occur again. 
Hence, food is a reinforcer, because it increases the probability that the behavior of 
pressing (formally referred to as the response of pressing) will take place. 
What kind of stimuli can act as reinforcers? Bonuses, toys, and good grades can 
serve as reinforcers—if they strengthen the probability of the response that occurred 
before their introduction. What makes something a reinforcer depends on individual 
preferences. Although a Hershey bar can act as a reinforcer for one person, an indi-
vidual who dislikes chocolate may fi nd one dollar more desirable. The only way we 
can know if a stimulus is a reinforcer for a particular organism is to observe whether 
the frequency of a previously occurring behavior increases after the presentation of 
the stimulus. 
Of course, we are not born knowing that one dollar can buy us a candy bar. 
Rather, through experience we learn that money is a valuable commodity because of 
its association with stimuli, such as food and drink, that are naturally reinforcing. 
This fact suggests a distinction between primary reinforcers and secondary reinforc-
ers. A primary reinforcer satisfi es some biological need and works naturally, regardless 
of a person’s previous experience. Food for a hungry person, warmth for a cold 
person, and relief for a person in pain all would be classifi ed as primary reinforcers. 
A secondary reinforcer , in contrast, is a stimulus that becomes reinforcing because of 
its association with a primary reinforcer. For instance, we know that money is valu-
able, because we have learned that it allows us to obtain other desirable objects, 
including primary reinforcers such as food and shelter. Money thus becomes a sec-
ondary reinforcer (Moher et al., 2008).