Methodological differences in test designs reveal differences in how dolphins understood a biosonar object discrimination task

In the late 1980s, Paul Nachtigall was able to obtain a new dolphin species for comparative biosonar studies, a false killer whale (Pseudorca crassidens) named Kina. The working hypothesis was that the larger false killer whale, which also hunted larger prey than the bottlenose dolphin, would not perform as well on a cylinder wall thickness discrimination task. However, Kina was able to resolve differences of approximately 0.7 mm during testing in 1992, compared with resolution values around 2.0 mm in multiple independent tests with dolphins. Branstetter (2020) explored the minimum discriminable time domain and frequency domain aspects of artificial echoes simulating returns from hollow cylinders but also noted the potential contribution of other aspects of echoes from physical objects. We will discuss the differences in animal training testing protocols and the amount of experience with the task as potential factors in the differences in performance that have been observed.