Not everyone who experiences traumatic events becomes clinically depressed. Some people rise to the challenges of adversity and overcome the stressful events. What determines who will succumb to depression? It may help to look at another perspective on depression, one claiming that depression is caused by the loss of a sense of personal control over one's life. This theory, based on the work of researcher Martin Seligman, is called learned helplessness. On the next screens you will see a demonstration of an experiment that led Seligman to develop this theory. We'll simplify the experiment a bit to emphasize the main points.
Learning to Escape Unpleasant EventsIn the 1960s, Martin Seligman and his colleagues studied how animals learn to escape shocks. In one of their experiments, they placed a dog in a shuttle box, a special cage that had a low barrier dividing the cage into two compartments. The floor of each half of the box had an electrical grid that could deliver a painful shock to the dog. The researchers could flip a switch to direct the electrical current to either compartment A or compartment B.
When the researchers turned on the shock in the dog's compartment (A), the dog jumped around frantically until it accidentally jumped over the barrier into the other compartment (B), escaping the shock.
When the researchers switched the shock to compartment B, once again the dog jumped around randomly until it accidentally crossed the barrier to safety.
After a few trials, the dog learned to expect the shock and would cross the barrier more quickly after the shock was turned on. This is called escape learning, because the dog was learning to get away from the shock. In terms of learning theory, the dog received negative reinforcement for crossing the barrier whenever the shock was turned on (ending the shock = reward).
Learning to Avoid Unpleasant EventsIn another variation of their experiments, the researchers turned on a light a few seconds before turning the shock on. They also used naive dogs that had not yet been tested in the box -- that is, dogs that had not already learned how to escape the shock. How do you think the dogs behaved?
In the early trials, when the researchers turned on the light, then turned on the shock in the dog's compartment (A), the dog jumped around frantically until it accidentally jumped over the barrier into the other compartment (B), escaping the shock.
After fifty trials, the dog learned to jump across the barrier to safety as soon as it felt the shock. But the dog was also learning something else: It was beginning to associate the light with the shock, realizing that the light was a warning that the shock was about to begin. Very quickly, the dog began paying attention to the light. As soon as the light came on, the dog jumped across the barrier, often jumping before the shock came on.
After fifty trials, the dog simply stood by the barrier, waiting until the light came on, and then calmly jumped across the barrier. This is called avoidance learning, because the dog was learning to anticipate the shock and to avoid it completely by responding to the warning signal.
Learned HelplessnessSo far, Seligman's research simply replicated what other researchers had already found -- naive dogs will quickly learn to escape unpleasant events and, if possible, to avoid those events entirely. But then Seligman tried something new. He strapped some of the dogs into a hammock and gave them inescapable shocks at random intervals. The next day, when these dogs were tested in the shuttle box, their behavior was very different from that of the naive dogs. Although, like the naive dogs, the dogs would jump around frantically as soon as they felt the shock, after a few seconds they would stop moving, lie down, and begin to whine.
On trial after trial, the dogs failed to escape; rather than jump across the barrier, the dogs passively accepted the painful shock.Seligman concluded that the dogs in the hammock had learned that they could not escape or avoid the shocks; that is, they had learned that they were helpless and that the shocks were uncontrollable. This conditioning was so powerful that when the dogs were placed in a situation in which they could escape the shock, they didn't even try, because they had formed the expectation that they could not control their environment. He called this behavior learned helplessness.
Ethical IssuesAlthough Seligman's findings have been widely accepted, animal-rights activists have criticized his use of painful, inescapable shocks. Was it necessary for the dogs to be shocked? Did the importance of the results justify the physical and psychological harm to the dogs? Questions such as these prompted the American Psychological Association to develop a set of ethical guidelines for the use of animals in research.