Establishing standardized conditions for clinically available sound-localization tests: A multicenter approach

Area of Science:

• Auditory Neuroscience
• Acoustics
• Psychoacoustics

Background:

• Sound localization is vital for auditory spatial awareness, relying on interaural time/level differences and spectral cues.
• Standardizing sound localization testing is essential for consistent clinical and research outcomes.

Purpose of the Study:

• To standardize sound localization testing conditions across Japanese facilities.
• To analyze the impact of early reflected sounds on localization accuracy.
• To compare localization performance between individuals with normal hearing and unilateral hearing loss.

Main Methods:

• Conducted sound localization tests with 77 normal-hearing and 45 unilateral hearing-impaired participants across 11 facilities.
• Used nine loudspeakers in a 180° arc, presenting CCITT and low-pass CCITT noise bursts (50-60 dB SPL).
• Measured early reflections (4-7 ms) using time-stretched pulses and assessed accuracy via root-mean-square error and mean deviation.

Main Results:

• Early reflections significantly reduced localization accuracy, with envelope area/peak values (4-7 ms) correlating with decreased performance (r = -0.535 to -0.555).
• Normal-hearing participants had a root-mean-square error of 2.0° ± 4.8°, while unilateral hearing loss participants showed significantly higher errors (68.4° ± 40.7°, p < .001).
• Left-right response asymmetry correlated positively with reflected sound characteristics (r > 0.6); noise type did not significantly impact performance.

Conclusions:

• Early reflections critically compromise sound localization accuracy, particularly in reverberant environments.
• Standardized testing protocols controlling early reflections are vital for reliable sound localization assessments.
• Optimizing acoustic conditions, including sound absorption, can improve test precision, especially for unilateral hearing loss evaluation.