Lateralization of high-frequency pure tones with interaural phase difference and bone conduction

Area of Science:

• Auditory Neuroscience
• Psychoacoustics
• Bioacoustics

Background:

• Interaural phase differences (IPDs) typically cue sound localization at low frequencies.
• High-frequency sound localization in humans usually relies on interaural level differences (ILDs).
• Bone-conduction hearing introduces unique acoustic challenges, including transcranial transmission.

Purpose of the Study:

• To investigate if interaural phase differences (IPDs) are converted to interaural level differences (ILDs) during bilateral bone-conduction stimulation.
• To determine the role of acoustic interference in transcranial transmission for sound localization.
• To explore inter-individual variability in bone-conduction hearing and localization.

Main Methods:

• Seven normal-hearing listeners participated in the study.
• Listeners judged the perceived lateral position of pure tones (3000-6000 Hz) presented via bilateral mastoid bone vibrators.
• Stimuli varied in interaural phase difference (IPD) to assess its effect on localization.

Main Results:

• Five out of seven listeners demonstrated sound lateralization, a phenomenon unexpected for pure tones at these frequencies using IPD.
• The direction of lateralization varied with frequency and IPD in three listeners.
• Significant inter-individual differences in lateralization were observed, possibly due to variations in transcranial transmission.

Conclusions:

• Findings support the hypothesis that external IPDs are converted to internal ILDs via acoustic interference during transcranial transmission with bone conduction.
• This conversion mechanism may explain sound lateralization observed with bone-conducted tones at high frequencies.
• The study suggests that established principles of air-conduction localization may not directly apply to bone-conduction hearing.