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Sunsay, Ceyhun

Psychology

2004

Ph. D.

Theoretical explanations of the trial spacing effect in Pavlovian conditioning were investigated in an appetitive conditioning preparation. Previous work suggested that a stimulus priming mechanism might be one of the causes of the trial spacing effect. However, the priming mechanism was shown to have a temporal limit of 240 s with the appetitive conditioning preparation. Experiment 1 showed that the trial spacing effect occurs well above this temporal limit, suggesting that another mechanism or mechanisms are also involved in producing the trial spacing effect. Experiment 2 used a design in which some rats were removed from the conditioning context during inter trial intervals (ITIs). The results supported the context blocking account as well as the comparator hypothesis but only with long ITIs. Experiment 3 attempted to contrast the context blocking account and the comparator hypothesis with a context deflation manipulation. The results varied with the type of dependent measures; however increases in performance were observed in groups that did not receive context deflation. Thus, the comparator hypothesis was not exclusively supported. Experiments 4 and 5 tested the accounts of the trial spacing effect with a within-subject design. While Experiment 4 failed to produce a trial spacing effect with short ITIs, Experiment 5 showed a trial spacing effect with relatively long ITIs which cannot be accommodated by contemporary models of conditioning. The results overall suggested two mechanism that might cause the trial spacing effect that occurs with long ITIs: Context blocking and stimulus fluctuation.