THE EFFECTS OF INTERPOLATED ITEMS ON THE LEARNING AND RETENTION OF INDIVIDUAL STIMULUS-RESPONSE (S-R) UNITS IN PAIRED-ASSOCIATE LEARNING WERE INVESTIGATED. EXPERIMENTS WERE DESIGNED TO DETERMINE THE EFFECTS OF INTERFERENCE PRODUCED BY OTHER ITEMS WHICH OCCUR NATURALLY WITHIN THE CONTEXT OF A STANDARD PAIRED-ASSOCIATE TASK. IN ADDITION, SEVERAL INVESTIGATIONS WERE CARRIED OUT IN THE GENERAL AREA OF COGNITIVE PROCESSING OF VERBAL INFORMATION. THE EFFECTS OF VARIATIONS IN LIST LENGTH (NUMBER OF ITEMS TO BE LEARNED SIMULTANEOUSLY) WERE STUDIED WITHIN THE CONTEXT OF A PAIR OF LEARNING MODELS. A RELATED PROBLEM WAS THE RELATIVE EFFICIENCY OF VARIOUS PART-LIST PROCEDURES. A FINAL SERIES OF EXPERIMENTS WAS CONCERNED WITH SHORT-TERM MEMORY PHENOMENA IN THE PROCESSING OF VERBAL INFORMATION. DATA FROM ALL THE STUDIES SUPPORTED THE GENERAL CONCLUSION THAT RETENTION OF SINGLE S-R UNITS IS DETERMINED BY MORE THAN ONE FACTOR. IN ADDITION TO THE NUMBER OF TIMES A UNIT HAS BEEN PRESENTED, THE NUMBER AND SPACING OF OTHER ITEMS TO BE LEARNED, THE STATE OF LEARNING, COMPATIBILITY OF INPUT AND OUTPUT MODES, AND PRIOR INFORMATION ABOUT MEMORY LOAD WERE CONSIDERED IMPORTANT. THEORETICAL MODELS WERE PROPOSED AND DISCUSSED IN RELATION TO THE DATA OBTAINED IN THE STUDIES. (JC)