Authors: Nele Naumann¹, Axel Ahrens¹
¹Hearing Systems Section, Department of Health Technology, Technical University of Denmark
Background: The auditory system uses interaural time and level differences (ITD and ILD) to localize sounds. Spectral weighting functions (SWFs) quantify the contribution of different frequency bands to lateralization judgments. Previous headphone studies showed ITD dominance at low frequencies and ILD dominance at high frequencies, while some free-field studies suggested a weight peak near 800 Hz. This study investigates how the auditory system integrates spatial information across frequency bands in a multi-source environment.
Method: SWFs were measured in normal-hearing listeners using 11 loudspeakers (±75°). In each trial, multiple frequency bands were presented simultaneously from independent locations, and listeners reported the perceived lateralization (left or right). Four conditions were tested: 11 ERB-spaced noise bands, 6 wide-spaced ERB bands, 7 octave-spaced tones (100–6400 Hz), and 7 harmonics of an 800 Hz tone. A reverse correlation approach was used to estimate the SWFs.
Results: In noise conditions, the highest weights were assigned to the highest frequency band, followed by the lowest band. In the octave-spaced tone condition, a one-sided edge effect was observed where the highest frequency dominated. Notably, no peak was found around 800 Hz in broadband conditions; high weights for 800 Hz only appeared when it served as the lowest frequency band in the stimulus.
Conclusion: When faced with conflicting spatial information across frequencies, the auditory system prioritizes spectral edges. The dominance of high-frequency bands suggests that ILDs contributed more strongly to the localization response than ITDs in this context. This reliance on high-frequency cues may help explain localization difficulties in individuals with hearing impairment, particularly in noisy environments where high-frequency information is often degraded.
