Short-Term Retention of Object Discriminations in Experienced and Naive Rhesus Monkeys

2 groups of adult rhesus monkeys, one learning-set-sophisticated (LS-S) and one learning-set-naive (LS-N), were trained on 360 object-quality discrimination problems. Each set of 6 daily problems was followed by one retention trial on each of the original problems. The order of the presentation of the retention trial was counterbalanced. The LS-S Ss had significantly higher acquisition scores and retained a greater absolute number of items than the LS-N Ss. But when the retention scores were adjusted for level of performance on Trial 6 of acquisition, the LS-N animals showed a significantly higher retention score. No serial or sequential effects were found and the results were interpreted as indicating that the learning-set procedure overloaded the short-term memory mechanism of both naive and sophisticated animals, thus eliminating sequence effects. The rapid forgetting of the characteristics of individual items in a learning-set situation would facilitate learning-set performance.