Predictable and Unpredictable Shock: Their Pathological Effects on Restrained and Unrestrained Rats

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Abstract
The effects on rats of predictable and unpredictable shock were measured under 2 conditions: unrestrained Ss were shocked intermittently for 12/24 hr. on a 6-hr. on, 6-hr. off schedule; restrained Ss were shocked intermittently for 12/24 hr. on a 6-hr. on, 6-hr. off schedule. All Ss were shocked via tail electrode; thus, for the first time, unrestrained rats were completely unable to avoid “unavoidable” shock. Under Condition I, Ss receiving unpredictable shock lost more weight than Ss receiving predictable shock. Under Condition II, more Ss in the unpredictable-shock group developed ulcers than Ss in the predictable-shock group. The findings of Weiss (1968, 1970) were partially confirmed and extended to unrestrained Ss.