Dolphins maintain high echolocation vigilance for eight hours without primary (food) reinforcement

Studies have demonstrated that dolphins can maintain continuous auditory or echolocation vigilance for up to 5 to 15 days when provided with continuous primary reinforcement (i.e., food reward after each correct detection). The goals of this study were to examine whether dolphins could perform an 8-h echolocation vigilance task featuring variable reinforcement schedules, where correct responses were intermittently rewarded, and variable acoustic secondary reinforcement (feedback) patterns. Three dolphins were trained to echolocate simulated targets and press a response paddle upon detecting echoes. Three conditioned reinforcement conditions were utilized: no (acoustic) feedback, acoustic feedback, and structured acoustic feedback. The probability of primary reinforcement following a correct response began at 50% for all dolphins but was sequentially reduced to 25%, 12%, 6%, and 0% each time performance criteria were met. Conditions including acoustic feedback resulted in two dolphins successfully performing the echolocation vigilance task under the 0% primary reinforcement schedule (8 h before receiving primary reinforcement). None of the animals reached 0% reinforcement probability in the no feedback condition. The results demonstrate that dolphins can perform experimental echolocation tasks for extended time periods without primary reinforcement and suggest that secondary reinforcement may be important to maintain this behavior.