Hisashi Hirai

Loss of controllability in appetitive situations interferes with subsequent learning in aversive situations

In two experiments, we examined whether or not a loss of control over food availability would interfere with subsequent two-way shuttle-escape learning. Rats that had experienced loss of control over food delivery were impaired in their acquisition of a shuttle-escape response, relative to the response-contingent and the continuous-reinforcement control rats (in Experiments 1 and 2) and to the lack-of-control and home cage control rats (in Experiment 2). Rats that had received noncontingent food delivery without a prior history of control over food exhibited poorer performance than did the home cage control rats. Moreover, loss of control resulted in a larger interference effect than did lack of control, supporting the view that the learning of response-outcome noncontingency is the main determinant of the interference effect.

Effects of unpredictability versus loss of predictability of shock on gastric lesions in rats

The relative importance of unpredictability versus loss of predictability of electric tail-shock affecting stress pathology was assessed by using an index of the severity of gastric lesions in male Sprague-Dawley rats. Although repeated sessions of unpredictable shock produced more severe gastric lesions in a greater percentage of rats than did repeated sessions of either predictable or no shock, there was no significant difference, in terms of both incidence and severity of lesions, between lack of predictability and loss of predictability. However, rats exposed first to unpredictable shock and subsequently to predictable shock had significantly fewer lesions than rats exposed continuously to unpredictable shock. The results emphasize only the deleterious effects of shock unpredictability. The effects of changes in predictability of shock on gastric erosions are not clearly supported by the results.

The role of predictability in preventing escape deficits following loss of control over food acquisition

The present experiment examined whether predictability of food acquisition would eliminate the impairment of subsequent escape performance that otherwise resulted from uncontrollability over food acquisition. In pretreatment, the yoked and the yoked-signal groups received response-independent food at the same times as the experimental group acquired it on an FR 5/20 lever-press schedule. However, a pellet presented for the yoked-signal group followed a 1.5-sqc tone, which served as a predictive signal of food. The naive control group received the same clumber of pellets in their home cages in this phase. Results of the escape latency in the subsequent FR 2 shuttling shock-escape test indicated that the predictability of outcome eliminated the escape deficits showed by the yoked-non signal group. This modulating effect of a predictive signal is hypothesized to be due to an overshadowing of uncontrollability by predictability.