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.

Modeling the utility of binaural cues for underwater sound localization.

The binaural cues used by terrestrial animals for sound localization in azimuth may not always suffice for accurate sound localization underwater. The purpose of this research was to examine the theoretical limits of interaural timing and level differences available underwater using computational and physical models. A paired-hydrophone system was used to record sounds transmitted underwater and recordings were analyzed using neural networks calibrated to reflect the auditory capabilities of terrestrial mammals. Estimates of source direction based on temporal differences were most accurate for frequencies between 0.5 and 1.75 kHz, with greater resolution toward the midline (2°), and lower resolution toward the periphery (9°). Level cues also changed systematically with source azimuth, even at lower frequencies than expected from theoretical calculations, suggesting that binaural mechanical coupling (e.g., through bone conduction) might, in principle, facilitate underwater sound localization. Overall, the relatively limited ability of the model to estimate source position using temporal and level difference cues underwater suggests that animals such as whales may use additional cues to accurately localize conspecifics and predators at long distances.

Acoustic cues available for ranging by humpback whales.

Field measurements of sound propagation in a humpback whale habitat were collected to identify cues that a humpback whale might use to estimate its distance from sound sources. The data show that spectral cues are sufficient for estimating the relative distance a sound has traveled in such environments, and that several other cues may also provide useful information. It is suggested that listening humpback whales may use multiple cues in parallel to determine the range to singing whales.