VALIDITY OF A DELAYED CONDITIONAL DISCRIMINATION TASK AS A MODEL FOR WORKING-MEMORY IN THE RAT

A delayed conditional discrimination (DCD) task in the rat was modifie d by requiring a response on an admission lever at the end of each del ay. This requirement proved effective in precluding the use of positio nal cues as mediating behavior. Furthermore, validity of the procedure was assessed by examining how performance changed as a result of: len gth of the delay, retroactive and proactive interference, and encoding time. Results showed that log d, a measure of stimulus discriminabili ty, decreased on longer delays (Experiment 1); decreased when an inter fering stimulus was presented during delays (Experiment 2); decreased when the intertrial interval was made shorter (Experiment 3); and decr eased when the sample stimuli were presented for a shorter period of t ime (Experiment 4). Log b, an index of bias, remained low throughout t he study, indicating that no significant response bias was present. Ta ken together, the results support the notion that this modified DCD ta sk is a valid model for working memory that effectively precludes the use of positional cues as mediating behavior in the rat.