Stimulus control of defensive reactions in the albino rat.

A series of studies are reported, examining the characteristics of stimuli that produce unconditioned defensive reactions in the rat. These studies show that neither the sound nor the smell of a cat, or the sight or a dead cat, will produce freezing, but either a moving cat or dog, or the abrupt and rapid movement of an inanimate card, will result in freezing and failure to approach the stimulus object. It is suggested that movement is a major factor in the initiation of defensive responses and that movement of a neutral stimulus may enhance the acquistion of defensive responses to that stimulus.