Signaling the Duration of Uncontrollable Shock Impairs Subsequent Shock Escape
An experiment was performed to investigate the effect of signaling the duration of uncontrollable shocks upon subsequent shock-escape acquisition. Rats were run in pentads, consisting of a controlling animal, three animals yoked for shock, and a no-shock animal. Shocks of 1.6-mA intensity occurred randomly with a mean density of 10 shocks/min. the controlling animal could reduce shock duration from 1-s (long) shocks to 0.3-s (brief) shocks by emitting a pair of lever presses within a 15-s interresponse time limit. One yoked animal received a 0.5-s houselight presentation each time the controlling animal responded, so that the interlight spacing was correlated with shock duration. A second yoked animal received an equal number of houselight presentations, the spacing of which was uncorrelated with shock duration, whereas a third yoked animal received no houselight presentations. the no-shock animal was exposed only to the houselight presentations produced by the controlling animal’s responding. After 9 to 18 training sessions, half of the pentads were tested for escape acquisition in an illuminated shuttlebox and half in a dark shuttlebox. Animals who received correlated light presentations during pretraining showed major interference with escape acquisition relative to all other animals. Those tested in the dark were more impaired in learning to escape than those tested in the light. Thus, animals preexposed to uncontrollable shock for which the duration was signaled showed impaired escape acquisition under conditions that led to no interference for animals preexposed to identical shocks for which the duration was not signaled. This extends previous findings on the major role of signaling when exposure to uncontrollable shock is chronic to the signaling of an aversive characteristic of such uncontrollable shock.
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