The dynamics of a dolphin’s biosonar signals while performing target discrimination tasks

Abstract

An experiment was conducted to determine if a blindfolded echolocating dolphin modified its biosonar signals depending on the targets it was investigating in a target shape discrimination task. Biosonar signals were measured with a specially designed bite-plate apparatus with a dowel extending from the bite plate to support the hydrophone. The detected signals were digitized and stored on a modified SoundTrap (Ocean Instrument New Zealand) attached to the dowel. The dolphin engaged in a matching-to-sample task: he first examined a sample target and then swam to a different area of the pool to examine three alternative targets, one of which matched the sample. The animal’s task was to point to the matched target. The characteristic of each emitted signal was determined by calculating the peak frequency, center frequency, rms bandwidth, and rms duration. A specific target set was used for each session of 15-18 trials; some sets were unfamiliar to the dolphin. Considerable amount of variations in the signal parameters were observed across trials and sessions, but our statistical analyses suggested the variations were not based on target identity, thereby leading us to conclude that the clicks emitted by the dolphin did not differ with the target set.