During a famous experiment, three groups of dogs were observed. The first group of dogs was placed in harnesses while the second group of dogs was fitted with shock collars and all were placed in boxes with a foot-operated switch. These dogs could stop a series of painful shocks at any time by pressing the switch. The third group of dogs was also fitted with shock collars and placed in boxes with a foot-operated switch, but the switches did not work and the dogs had no control over the duration or intensity of each electric shock. Eventually, the dogs in the third group stopped pressing the switch. These dogs became passive and depressed. What theory explains the behavior of the dogs in the third group?
