### Spontaneous Recovery

Suppose that by the end of the second class, Adam has completely stopped cringing when Professor Smith pulls out the revolver. His conditioned response has been extinguished. However, if Professor Smith comes into class later in the semester and pulls out the revolver again, Adam may still cringe, though maybe a little less than before. This is called spontaneous recovery. Spontaneous recovery is the reappearance of an extinguished conditioned response when the conditioned stimulus returns after a period of absence.

### Stimulus Generalization

Now suppose Professor Smith conditions Adam again to respond to the revolver as she did in the first class. Soon he cringes every time she pulls out the revolver. While Adam is in this conditioned state, the professor pulls out a cell phone. Adam is likely to cringe at that too because of stimulus generalization—the tendency to respond to a new stimulus as if it were the original conditioned stimulus. Stimulus generalization happens most often when the new stimulus resembles the original conditioned stimulus.

Example: In the 1920s, the behaviorist John Watson and his colleague Rosalie Rayner did a famous study that demonstrated stimulus generalization. They gave a white rat to an eleven-month-old boy named Little Albert, who liked the rat and enjoyed playing with it. In the next stage of the experiment, the researchers repeatedly made a loud noise behind Albert while offering him the rat. Each time, Albert fell to the floor, frightened. When the researchers then offered the rat to him without making the noise, Albert showed fear of the rat and crawled away from it. The researchers were subsequently able to generalize Albert’s fear to other furry, white stimuli, including a rabbit, a dog, a fur coat, a Santa Claus mask, and Watson’s hair. This experiment is considered highly unethical by today’s standards.

### Stimulus Discrimination

Suppose Professor Smith used a gray revolver to condition Adam. Once Adam is conditioned, if she pulls out a brown revolver, he’ll initially cringe at that, too. But suppose Professor Smith never shoots when she pulls out the brown revolver and always shoots when she pulls out the gray one. Soon, Adam will cringe only at the gray revolver. He is showing stimulus discrimination—the tendency to lack a conditioned response to a new stimulus that resembles the original conditioned stimulus.

### Higher-Order Conditioning

Now suppose that after Adam has been conditioned to cringe at the sight of the revolver, Professor Smith comes to class one day and pulls out the revolver while yelling, “Fire!” She does this many times. Each time, Adam cringes because he is conditioned to respond to the revolver. If she then yells, “Fire!” without pulling out the revolver, Adam will still cringe due to higher-order conditioning—the process by which a neutral stimulus comes to act as a conditioned stimulus by being paired with another stimulus that already evokes a conditioned response.