Auditory Processing by Dolphins of Signals Related to Signature Whistles

Abstract

It is now well established (Caldwell and Caldwell, 1970) that one of the major forms—if not the major form—of dolphin communication is the signature whistle. In an effort to obtain information concerning the types and levels of auditory discriminations dolphins must be able to make if they are to process these calls, ah extended series of related studies is being conducted. In the first investigation, the research focus was on auditory pattern recognition within three domains: those of frequency, time, and acoustic configuration. Specifically, a “master” dolphin whistle was patterned and synthesized—as were three other whistles varying only with respect to their frequency, temporal, or spatial characteristics, respectively. Additionally, sets of synthesized whistles were obtained for several equally spaced intermediate points along each of the three experimental continua; all signals were generated through the courtesy of the Speech Transmission Laboratory, Royal Institute of Technology, Stockholm, Sweden. For the three substudies, an experimental animal (an Atlantic Bottlenose dolphin) was administered 50 trials (25 stimuli each) of the “master” whistle and one of the experimental stimuli. Following completion of this procedure, a second set of 50 trials would compare the master whistle with another set of experimental signals; these sets were always ordered from the most different comparisons to the least different within a substudy. Once all data were obtained from one substudy (frequency, say), the whole procedure was replicated for the next. With one exception, the experimental animal was able to discriminate between all stimuli—even those that were almost identical. A discussion of these results and a review of the direction of subsequent research will be provided.