Changes in dolphin echo-delay jitter detection thresholds when the number of jittering echoes is limited

Dolphins use echo-delay to determine the range and movement of a target. Echo-delay “jitter” tasks require the dolphin to discriminate between simulated echoes with fixed delay and those with delay “jitter” (delay increases and/or decreases on successive echoes). While there have been several studies looking at dolphin echo-delay jitter-detection thresholds, results have varied based on the duration of time that the jittering echo was available. Additionally, previous experiments suggest that dolphins integrate information across multiple echoes to detect objects, but little is known about how echo-delay jitter detection may be affected when the number of echoes is limited. In this experiment a bottlenose dolphin (Tursiops truncatus) was trained to echolocate, listen to returning electronic “phantom” echoes, and produce a conditioned acoustic response if jitter was detected. Jitter detection thresholds were measured when the dolphin had access to 1, 3, 5, 9, 17, 33, or an unlimited number of jittering echoes. Thresholds decreased with increasing number of echoes, with the largest decrease observed between five and nine echoes (thresholds of 46 versus 1.6 μs, respectively), and then plateaued as the number of jittering echoes increased above nine. [Work supported by ONR.]