Date of Award


Degree Type


Degree Name

Doctor of Philosophy


A series of three experiments examined the forgetting of visual discriminations in pigeons. The problems consisted of feature discriminations, with dot displays as the discriminative stimuli, and involved a successive go/no-go pecking-response. It was found in all three experiments that pigeons that had been trained to refrain from pecking an S- display, resumed pecking at these displays after retention intervals. It was argued that these data represent the first unequivocal demonstration of forgetting of discriminations in pigeons.;In addition to the simple demonstration of forgetting, it was found in Experiment 1 that the amount of forgetting progressively increased, in a negatively accelerated fashion, over intervals of 1, 10 and 20 days. Also, it was found that more forgetting occurred for a reverse discrimination than for a single discrimination. In Experiment 2 it was found that acquisition was retarded and more forgetting occurred for discriminations which involved highly similar stimuli. It was argued that these data represent the first reported instance of intraproblem similarity effects on retention in animals. In Experiment 3 the role of contextual cues on forgetting was examined. It was found that a change in contextual cues between acquisition and retention testing enhanced forgetting, when the contextual cues present during original acquisition were conspicuous; when these cues were relatively inconspicuous, a change in context had no effect on forgetting.;A retrieval failure model of memory processing was described and applied to the data from each of the three experiments. It was argued that forgetting of discriminations involves selective retrieval failure of specific target memories, as a result of changes in the retrievability of these memories over time. An explicit conceptual mechanism was postulated as a source of these changes in retrievability.



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