Chickadees fail standardized operant tests for octave equivalence
Octave equivalence occurs when an observer judges notes separated by a doubling in frequency perceptually similar. The octave appears to form the basis of pitch change in all human cultures and thus may be of biological origin. Previously, we developed a nonverbal operant conditioning test of octave generalization and transfer in humans. The results of this testing showed that humans with and without musical training perceive the octave relationship between pitches. Our goal in the current study was to determine whether black-capped chickadees, a North American songbird, perceive octave equivalence. We chose these chickadees because of their reliance on pitch in assessing conspecific vocalizations, our strong background knowledge on their pitch height perception (log-linear perception of frequency), and the phylogenetic disparity between them and humans. Compared to humans, songbirds are highly skilled at using pitch height perception to classify pitches into ranges, independent of the octave. Our results suggest that chickadees used that skill, rather than octave equivalence, to transfer the note-range discrimination from one octave to the next. In contrast, there is evidence that at least some mammals, including humans, do perceive octave equivalence.
KeywordsBiological relevance Black-capped chickadees Pitch chroma Pitch height Octave equivalence
All animal studies were conducted in accordance with the Canadian Council on Animal Care Guidelines and Policies with approval from the Animal Care and Use Committee for Biosciences for the University of Alberta and the Life and Environmental Sciences Animal Care Committee for the University of Calgary Life. Chickadees were captured, and the research was carried out under an Environment Canada Canadian Wildlife Service Scientific permit, Alberta Fish and Wildlife Capture and Research permits, and City of Edmonton Parks Permit. This research was supported by a Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant and Discovery Accelerator Supplement, an Alberta Ingenuity Fund (AIF) New Faculty Grant, Canada Foundation for Innovation (CFI) New Opportunities and infrastructure Operating Fund Grants, along with start-up funding, and CFI partner funding from the University of Alberta to CBS. MH was supported by a NSERC post-graduate scholarship, an AIF graduate student scholarship, and an Izaak Walton Killam Memorial Scholarship (IWKMS). LMG was also supported by an IWKMS. We would like to thank our research assistants, Daniel Lee and Jill Avis, for their help conducting and monitoring the experiment. We would also like to thank our technical assistants, Lou Omerzu and Isaac Lank, for their help in developing and maintaining our apparatus.
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