Nest material and food as reinforcers for fixed-ratio responding in mice

Abstract

Three experiments investigated the importance of operant-reinforcer distance as a factor affecting continuous reinforcement (CRF) and fixed-ratio (FR) performance in mice, with nest material and food as reinforcers. In Experiment 1, nest material (paper strips) was presented on a series of FR schedules of increasing size, with the operandum located as close as possible to the reinforcer dispenser. Subjects compensated for increases in FR size by proportionately increasing their response output, but ratio strain occurred at low FR values. In Experiment 2, response rate was found to be inversely related to operant-reinforcer distance on a CRF schedule with nest material as reinforcer. In Experiment 3, food was presented on a series of FR schedules at two levels of deprivation, and with three operant-reinforcer distances. Operant-reinforcer distance was found to affect CRF response rate, degree of compensation for increases in FR size, and occurrence of ratio strain, but only when deprivation level was low. The results support the view that nest material and food share fundamentally similar reinforcing properties, but that nest material is a weaker reinforcer under normal test conditions.