Pinna-based spectral cues for sound localization in cat

Area of Science:

• Acoustics
• Auditory Neuroscience
• Bioacoustics

Background:

• The tympanic membrane (TM) plays a crucial role in auditory perception.
• Understanding how sound waves interact with the TM is essential for deciphering sound localization mechanisms.
• Previous research has explored sound localization cues, but the specific directional transfer functions near the TM require further investigation.

Purpose of the Study:

• To measure and analyze the directional dependence of the transfer function from free-field plane waves to a point near the feline tympanic membrane (TM).
• To investigate the utility of these transfer functions as cues for sound localization in terms of azimuth and elevation.

Main Methods:

• Measurements were conducted in anesthetized domestic cats using a probe tube microphone placed near the TM.
• Transfer functions were calculated as the spectral ratio of clicks recorded near the TM to those in the free field.
• Analysis focused on low (<5 kHz), mid (5-18 kHz), and high (>18 kHz) frequency ranges.

Main Results:

• Transfer functions exhibited significant directional dependence across all analyzed frequency ranges.
• A prominent spectral notch was observed in the mid-frequency range (5-18 kHz).
• Source direction was found to be uniquely determined by the transfer function, particularly for frontal sound sources, using mid-frequency spectral notch information.

Conclusions:

• The spectrum of broadband sound at the TM can serve as a robust cue for sound localization, encoding both elevation and azimuth.
• Mid-frequency spectral notches provide unique identifiers for sound source direction in front of the cat.
• These findings contribute to understanding the acoustic input to the auditory system and models of sound propagation in the ear canal.