Effects ofU ncontro llab le Aversive Events: Some
Psychology Press eBooks · 2000
Overmier and Seligman (1967) proposed that the inescapabilty of shock in the hammock was responsible for the failure to escape in the shuttlebox and suggested that an experiment comparing the proactive effects of escapable and inescapable shocks on subsequent escape learn ing should be done to test that hypothesis. Seligman and Maier (1967) conducted such an experiment, using the three-group or triadic design that has become the standard for research in this area. Plexiglas panels were placed on both sides of the dogs&s; heads as they lay in the ham mock. Dogs in the escapable shock group could terminate shocks by pressing either panel once. Dogs in the inescapable shock group had nonfunctional panels. The duration of each shock for a dog in the ines capable shock group was matched or yoked to that of a dog in the escape group, so that the two dogs received the same pattern of shock dura tions across trials. Thus operationally only the escapability of shocks distinguished the two groups. Dogs in the third group were simply re strained in the hammock. When the dogs were tested in the shuttlebox the next day, escape learning of the previously inescapably shocked dogs was profoundly impaired. Most failed to learn, receiving the full 30 sec of shock on 9 or more of the 10 trials. In contrast, the escape re sponse was learned quickly by nearly all the dogs in the other two groups, which did not differ.