An individual differences pure extinction process

A pure extinction process memory retrieval latency model is completely characterized by the number of items to be recalled n and the recall rate λ. In this paper λ is allowed to vary across the population of subjects. Results are given for arbitrary individual differences distributions on λ. When λ is distributed gamma the results are very simple and method of moment estimators are easily obtained. In addition the shape parameter of the gamma individual differences distribution turns out to be an index of the degree of heterogeneity of the recall parameter. The pure extinction process model is also appropriate for certain collection and detection tasks.