Periodicity pitch difference limens in the bottlenose dolphin (Tursiops truncatus)

An Atlantic bottlenose dolphin (Tursiops truncatus) was trained to differentiate between similar streams of sonarlike pulse pairs. The interval between pulses of a pair was of primary interest and was varied from trial to trial. All signal parameters were designed to simulate the emitted signals and returned echoes present in a dolphin sonar task. Discriminative responding to variations in the interpulse interval allowed for an estimation of the dolphin's temporal discrimination ability. Psychophysical functions constructed from the data were orderly, asymptotic, monotonically related to the duration of the comparison intervals, and statistically reliable. Psychophysical thresholds, defined as the 75% correct level of responding, indicated that the dolphin was capable of resolving differences as fine as 100 μsec. Further, the results confirmed that the dolphin's temporal discrimination is most accurate for pulse pair intervals simulating the shortest distances. Results were interpreted within the framework of a periodicity pitch analysis. Extrapolation of the data suggest that sonar discrimination of distance in the dolphin involves a complex frequency discrimination rather that a correlation discrimination.