Infant does not value cash, but does value milk. A medal, a diploma, and a trophy

all provide examples of secondary reinforcers.

One of the important phenomena associated with operant conditioning is

extinction. Earlier, we discussed how extinction takes place when the conditioned

stimulus is presented a number of times without the unconditioned stimulus.

Extinction also takes place when the frequency of a category of operant responses

declines. If, using the operant conditioning apparatus, reinforcement is withheld

from a rat, then lever pressing for food will decline and eventually diminish to

nearly zero. The organism has learned to give up a given operant because it no

longer brings the reinforcer.

Both animal and human research on extinction suggest that it is a better way

to “break” bad habits than is punishment. If a way can be found to eliminate the

reinforcer (or reinforcers) linked to a behavior pattern, the behavior is likely to

be given up. Punishment tends to temporarily suppress the appearance of an

operant, but extinction has not necessarily taken place. Consequently, the

unwanted operant has “gone underground,” and may in time surface as an

unpleasant surprise. Also, punishment is frustrating to organisms and tends to

make them more aggressive.

Another important phenomenon associated with operant conditioning is the

partial reinforcement effect, the tendency of operant behavior acquired under

conditions of partial reinforcement to possess greater resistance to extinction than

behavior acquired under conditions of continuous reinforcement. Let’s say that rat

1 is reinforced every time it presses a lever; this rat is receiving continuous reinforcement. Rat 2 is reinforced every other time it presses a lever; this rat is receiving

partial reinforcement. Both rats will eventually acquire the lever-pressing response. Now assume that reinforcement is withheld for both rats. The rat that will, in most cases, display greater resistance to extinction is rat 2. Skinner was surprised

by this result. If reinforcement is a kind of strengthening of a habit, then rat

1, receiving more reinforcement, should have the more well-established habit.

And it should demonstrate greater resistance to extinction than rat 2.

Nonetheless, the partial reinforcement effect is a reality, and Skinner became

interested in it. He and his coworkers used many schedules of reinforcement to

study the partial reinforcement effect. In general, it holds for both animals and

human beings that there is indeed a partial reinforcement effect. Random reinforcement is determined by chance, and is, consequently, unpredictable. If behavior is acquired with random reinforcement, it exaggerates the partial reinforcement

effect. Skinner was fond of pointing out that random payoffs are associated

with gambling. This explains to some extent why a well-established gambling habit is hard to break.

Assume that an instrumental conditioning apparatus contains a light bulb.

When the light is on, pressing the lever pays off. When the light is off, pressing

the lever fails to bring forth a reinforcer. Under these conditions, a trained experimental animal will tend to display a high rate of lever pressing when the light is

on and ignore the lever when the light is off. The light is called a discriminative

stimulus, meaning a stimulus that allows the organism to tell the difference

between a situation that is potentially reinforcing and one that is not. Cues used

to train animals, such as whistles and hand signals, are discriminative stimuli.

Skinner notes that discriminative stimuli control human behavior, too. A factory

whistle communicating to workers that it’s time for lunch, a bell’s ring for a

prizefighter, a school bell’s ring for a child, and a traffic light for a driver are all

discriminative stimuli. Stimuli can be more subtle than these examples. A lover’s

facial expression or tone of voice may communicate a readiness or lack of readiness

to respond to amorous advances.

Skinner asserts that in real life both discriminative stimuli and reinforcers automatically control much of our behavior.