Abstract
The ability to discriminate changes in the fine structure of complex sounds is well developed in birds. However, the precise limit of this discrimination ability and how it is used in the context of natural communication remains unclear. Here we describe natural variability in acoustic fine structure of male and female zebra finch calls. Results from psychoacoustic experiments demonstrate that zebra finches are able to discriminate extremely small differences in fine structure, which are on the order of the variation in acoustic fine structure that is present in their vocal signals. Results from signal analysis methods also suggest that acoustic fine structure may carry information that distinguishes between biologically relevant categories including sex, call type and individual identity. Combined, our results are consistent with the hypothesis that zebra finches can encode biologically relevant information within the fine structure of their calls. This study provides a foundation for our understanding of how acoustic fine structure may be involved in animal communication.
Highlights
One of the great challenges facing ethology since its inception has been to understand the sensory and perceptual world an organism lives in
We describe natural variability in the acoustic fine structure within and between calls; we show that such natural variability is discriminable; and we provide evidence that fine structure may carry biologically relevant information
Our results are consistent with the hypothesis that the zebra finch’s perceptual sensitivity to acoustic fine structure is matched to the ability of the syrinx to produce variability in fine structure, as represented by periods in the time-waveform
Summary
One of the great challenges facing ethology since its inception has been to understand the sensory and perceptual world an organism lives in. Whereas humans only have 3 cone-opsin proteins (the main determinant for cone cell sensitivity) in the eye which underlie color vision, many avian species have 4 (e.g.2) and fish can have 5–10 (reviewed in[3]) This highlights the fact that even for common species, we are continually expanding our basic understanding of a species’ “umwelt” and growing in our appreciation of how species differ in their perceptual abilities. Fine structure as we define it is reflected in the relative amplitude of individual harmonics, broadly relatable to timbre, and zebra finches are sensitive to manipulations of the relative amplitude of harmonics[9,10,11,12], especially of lower harmonics[10,12] The limits of this discriminatory ability remain unclear, especially with regards to the acoustic variation in natural vocal signals, as well as how such perceptual abilities contribute to acoustic communication in this species. Note that in this paper we will use temporal fine structure with respect to human research and acoustic fine structure with respect to non-human animal research due to subtle differences in the methodologies and frameworks used between the human and animal research
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