ABSTRACT
A generation ago, while testing some predictions derived from the two-process theory of avoidance learning, researchers in Richard Solomon’s laboratory at the University of Pennsylvania discovered a dramatic effect of exposure to inescapable aversive events. Dogs were restrained in a hammock and given many painful, inescapable foot shocks. A day later they were placed in a shuttlebox, a chamber with two compartments separated by a shoulder-high barrier, and given electric shocks through the grid floor that would be turned off when they crossed from one side to the other. These dogs showed a marked impairment in learning to escape shock in the shuttlebox. Most of them failed to learn to escape. This was an impressive effect, because nearly all of the control dogs that had simply been restrained in the hammock on the preceding day readily learned to escape (Overmier & Seligman, 1967).
