An index of the magnitude of postshock crouching was obtained for rats given a single 1-sec. footshock and tested in the same situation or in a different situation. The shocked Ss crouched significantly more than nonshocked controls only in the situation in which shock had been given, indicating that crouching is elicited by stimulus cues associated with a single shock. Additional experiments indicated that crouching is not similar to the immobility postures acquired during continuous shock. The results were interpreted as indicating that crouching may be an index of fear.

When shock was given in a circular runway, a single shock from a moving shock prod produced reliable prod avoidance and reliably decreased intertrial interval activity for a group of male rats. Also, a reliable positive correlation was obtained for avoidance scores and intertrial activity in these Ss. Rats shocked by the prod outside the runway were more active in the runway and had higher prod-avoidance scores than rats shocked in the runway. The results were interpreted to indicate that fear may be conditioned in a single shock trial, and that fear produces reactions which vary with certain characteristics of the fear-eliciting stimulus: Fearful situations produce immobility, while discrete approaching stimuli which elicit fear produce active avoidance.

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