Drug effects on memory in the pigeon : analysis using the behavioural model of signal detection
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
This thesis is concerned with the application of the behavioural model of signal detection to the analysis of the effects of chlorpromazine (CPZ) and haloperidol on memory in pigeons. Memory is conceptualized as behaviour under delayed stimulus control. The behavioural model of signal detection provides a way of determining a bias-free measure of discriminability and the extensions of the model to account for delayed discrimination performance allow the locus of drug effects to be determined in a quantitative manner. In Experiment 1, pigeons worked on a delayed matching-to-sample procedure where the reinforcement rate was controlled to prevent the development of response biases. Five doses of CPZ were administered (0.5-15.0 mg/kg). There was a significant dose-dependent decrease in matching performance at doses that had no significant effect on measures of psychomotor performance. CPZ had no differential effect on matching performance as a function of the delay interval. When the performance-by-delay interval data were fit to the negative exponential and rectangular hyperbolic functions, in both cases there was a decrease in the initial discriminability but no change in the rate of decrement of discriminability. This suggested the drug was affecting the behavioural processes of discrimination, encoding, and retrieval and not memory or retention processes. This model of CPZ action was in agreement with previous research assessing the effect of CPZ on memory, In Experiment 2, this model of CPZ action was investigated. The sample stimulus response requirement was systematically changed from FR5 to FR1. The effect on performance mimicked the effects of CPZ in Experiment 1, and suggested that both manipulations were affecting the same behavioural processes, i.e., discrimination, encoding, and retrieval. In Experiment 3 it was shown that the effect of CPZ could be compensated for by increasing the sample stimulus response requirement prior to drug administration. This raised the baseline level of performance and reduced the drugs' decremental effect on matching performance. In Experiment 4,the effects of haloperidol (0.06-0.30 mg/kg) were assessed, but due to insufficient data the method of analysis derived from the behavioural model of signal detection could not be applied. It was found that the drug caused a greater decrease in matching and psychomotor performance than CPZ at doses that were approximately equivalent to the doses of CPZ administered in Experiment 1. Further the effect of haloperidol could also be characterized as a decrease in the initial discriminability but no effect on the rate of decrement in discriminability across the delay intervals. The results are discussed in terms of methodological issues involved in the application of the behavioural model of signal detection to the analysis of drug effects. A model of the effects of CPZ and haloperidol is developed and the clinical implications are discussed. Finally the implications of the results in terms of models of pigeon memory and the analysis of behaviour in general are briefly examined.