Story of Psychology - Morton Hunt [177]
Making good use of his mechanical aptitude, he constructed a puzzle box that was a great improvement over the Thorndike model; widely used ever since, it is known as the Skinner box. In its basic form—it has many models—it is a cage, large enough to comfortably accommodate a white rat, with a horizontal bar on one wall just above a little food tray and a water spout. When the rat, prowling about the cage, happens to rest its forepaws on the bar, pressing it down, a food pellet automatically drops into the tray. Connected equipment outside the cage automatically records the behavior by drawing a line showing the cumulative number of bar pressings minute by minute. This was a much more efficient way of gathering data than Thorndike’s puzzle box procedure, since the experimenter did not have to observe the rat or deliver the food when it pressed the bar but merely look at the record.
The box also yielded more objective data on the acquisition or extinction of behavior than anyone had gathered thus far. The rat, and it alone, determined how much time elapsed between one pressing of the bar and the next. Skinner could base his findings of learning principles on the “response rate”—the rate at which the animal’s behavior changed in response to reinforcement—uncontaminated by the experimenter’s actions.
Moreover, Skinner could program the box in ways that approximated many circumstances in the real world that either reinforce or fail to reinforce behavior. He could, for instance, study the learning of a response when it is regularly rewarded; the extinction of a learned response when the reward is abruptly discontinued; the effects on learning and on extinction when rewards are delivered intermittently at regular intervals (say, every fourth bar pressing); the effects when rewards are delivered intermittently at irregular intervals; the effects of mixed results of bar pressing (such as a reward coupled with an electric shock); and so on. In each case, the data yielded a curve showing the rate of acquisition or extinction of a behavior under those particular circumstances.
From these curves, Skinner formulated a number of principles that cast light on the behavior of rats—and human beings. An example is his discovery of an important variation of the partial reinforcement effect. After rats had been trained on a schedule in which food pellets were delivered only once in a while and at irregular intervals, the rats would persist in their bar pressing even if the food-dispensing apparatus was turned off altogether. Their learned behavior was more resistant to extinction than that of rats trained to intermittent but regular reinforcement.56 This has been likened by some to the behavior of a slot machine player in a casino: neither the rat nor the gambler has any way of predicting when the next reinforcement is to come, but, being accustomed to occasional rewards, will hang on in the hope of getting one on the next try.57
Skinner’s most important contribution, however, was his concept of “operant conditioning”; for this alone he merits a permanent place in the Hall of Fame of psychology.
In “classical” (Pavlov’s) conditioning, the animal’s unconditioned response (salivating) to food is made into a conditioned response to a formerly neutral stimulus (the sound of the metronome or bell); the crucial element in the behavior change is the new stimulus.
In “instrumental” (Thorndike’s) conditioning, the crucial element in behavior change is the response, not the stimulus. A neutral response— the accidental stepping on the treadle during random efforts to get to the food—is rewarded and becomes a learned bit of behavior serving an end it formerly did not have.
Skinner’s operant conditioning is an important development in instrumental conditioning.