Properties of low-frequency head-related transfer functions in the barn owl (Tyto alba)
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The barn owl (Tyto alba) possesses several specializations regarding auditory processing. The most conspicuous features are the directionally sensitive facial ruff and the asymmetrically arranged ears. The frequency-specific influence of these features on sound has consequences for sound localization that might differ between low and high frequencies. Whereas the high-frequency range (>3 kHz) is well investigated, less is known about the characteristics of head-related transfer functions for frequencies below 3 kHz. In the present study, we compared 1/3 octaveband-filtered transfer functions of barn owls with center frequencies ranging from 0.5 to 9 kHz. The range of interaural time differences was 600 μs at frequencies above 4 kHz, decreased to 505 μs at 3 kHz and increased again to about 615 μs at lower frequencies. The ranges for very low (0.5–1 kHz) and high frequencies (5–9 kHz) were not statistically different. Interaural level differences and monaural gains increased monotonically with increasing frequency. No systematic influence of the body temperature on the measured localization cues was observed. These data have implications for the mechanism underlying sound localization and we suggest that the barn owl’s ears work as pressure receivers both in the high- and low-frequency ranges.
KeywordsSound localization Interaural time difference Interaural level difference Acoustic Auditory
Fast Fourier transformation
Head-related transfer function
Head-related impulse response
Interaural time difference
Interaural level difference
We thank Frank Endler for help with the setup and stimulus software, and Gillian Melton for proofreading. Care and treatment of the owls were approved by the Landespräsidium für Natur, Umwelt und Verbraucherschutz Nordrhein-Westfalen, Recklinghausen, Germany, and principles of laboratory animal care (NIH publication No. 85-23, revised 1985) were followed.
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