Individual differences in external-ear transfer functions of cats

Area of Science:

• Bioacoustics
• Auditory Neuroscience
• Comparative Anatomy

Background:

• Understanding external ear acoustics is crucial for spatial hearing research in animals.
• Directional transfer functions (DTFs) characterize how external ears filter sound based on direction.
• Individual variations in DTFs can influence the interpretation of auditory spatial cues.

Purpose of the Study:

• To quantify individual differences in the directional transfer functions (DTFs) of cat external ears.
• To investigate the impact of frequency scaling on reducing inter-cat variability in DTFs.
• To provide guidelines for applying DTF measurements across different cats in research.

Main Methods:

• Measured DTFs in 24 anesthetized cats with ears fixed frontally.
• Analyzed DTFs across a mid-frequency range (8-16 kHz) and 30 spatial locations.
• Quantified inter-cat differences and assessed the effect of frequency scaling and body weight correlation.

Main Results:

• DTFs exhibited similar direction dependence across cats but varied in spectral feature frequencies (e.g., notches varied by nearly a factor of 2).
• Frequency scaling reduced inter-cat differences, with optimal scale factors up to 1.57 correlating with body weight.
• Significant individual differences in DTFs persisted even after frequency scaling, exceeding variability from ear positioning.

Conclusions:

• Substantial individual variability exists in cat external ear acoustics, affecting spatial hearing.
• Frequency scaling offers a partial solution for standardizing DTF measurements across individuals.
• Results inform the conditions under which DTF data from one cat can be generalized to others.