Recognition of Frequency Modulated Whistle-Like Sounds by a Bottlenose Dolphin (Tursiops truncatus) and Humans with Transformations in Amplitude, Duration and Frequency.

Brian K Branstetter,Brandon Dziedzic,Kimberly Bakhtiari,Caroline M Delong,Amy Black

doi:10.1371/journal.pone.0147512

Brian K Branstetter, Brandon Dziedzic + Show 3 more

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https://doi.org/10.1371/journal.pone.0147512

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Abstract

Bottlenose dolphins (Tursiops truncatus) use the frequency contour of whistles produced by conspecifics for individual recognition. Here we tested a bottlenose dolphin’s (Tursiops truncatus) ability to recognize frequency modulated whistle-like sounds using a three alternative matching-to-sample paradigm. The dolphin was first trained to select a specific object (object A) in response to a specific sound (sound A) for a total of three object-sound associations. The sounds were then transformed by amplitude, duration, or frequency transposition while still preserving the frequency contour of each sound. For comparison purposes, 30 human participants completed an identical task with the same sounds, objects, and training procedure. The dolphin’s ability to correctly match objects to sounds was robust to changes in amplitude with only a minor decrement in performance for short durations. The dolphin failed to recognize sounds that were frequency transposed by plus or minus ½ octaves. Human participants demonstrated robust recognition with all acoustic transformations. The results indicate that this dolphin’s acoustic recognition of whistle-like sounds was constrained by absolute pitch. Unlike human speech, which varies considerably in average frequency, signature whistles are relatively stable in frequency, which may have selected for a whistle recognition system invariant to frequency transposition.

Highlights

Whistle use by bottlenose dolphins serves several functions including broadcasting individual identification [1,2,3], a vocal label to address individual conspecifics [4], maintaining group cohesion [5, 6], long range communication [7, 8], recruitment during feeding [9] and advertising emotional state [10, 11]
For all animal listeners in general, changes in sound amplitude are constantly occurring due to changing distances between sound sources and listeners, environmental reverberation as well as natural sound pressure level (SPL) variation produced by an animal
It’s not surprising that both the dolphin and human listeners recognized the test sounds despite a 20 dB range in SPL

Summary

Introduction

Whistle use by bottlenose dolphins serves several functions including broadcasting individual identification [1,2,3], a vocal label to address individual conspecifics [4], maintaining group cohesion [5, 6], long range communication [7, 8], recruitment during feeding [9] and advertising emotional state [10, 11]. One whistle type that has been the focus of much study is the PLOS ONE | DOI:10.1371/journal.pone.0147512. Whistle Recognition by a Dolphin and Humans analysis, decision to publish, or preparation of the manuscript One whistle type that has been the focus of much study is the PLOS ONE | DOI:10.1371/journal.pone.0147512 February 10, 2016

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