Diotic Narrowband Noises Can Be Perceived as Intracranially Off Center in Listeners With Clinically Symmetrical Audiometric Thresholds

Speaker: Obada AlQasem (UMD, HESP)

Abstract: The localization of sound sources in the horizontal plane depends on the interaural time difference (ITD) and interaural level difference (ILD). It is assumed that individuals with normal and symmetrical hearing thresholds perceive stimuli with zero ILD and ITD as fused, centered auditory images, which is not always accurate. This study investigated ILD lateralization bias in individuals with normal hearing. This study explored whether these biases correlate with interaural hearing threshold asymmetries within the clinical criteria (i.e., ≤ 10 dB HL) and interaural loudness perception asymmetry. ILD lateralization and across-ear loudness balancing tasks were conducted to examine ILD lateralization bias and loudness asymmetries on three separate days. The stimuli comprised a wideband noise and a set of 1 ERB wide narrowband noises centered at 0.25-8 kHz. The results demonstrated that at the individual level, participants consistently exhibited ILD lateralization biases and perceptual loudness imbalance at different frequencies. These lateralization biases and loudness imbalances were consistent across the three measurement days and were not attributable to individual variability. Furthermore, they were not caused by improper headphone placement, as the headphones were reversed between blocks. Audiometry indicated no hearing threshold asymmetries beyond the clinical criteria. Correlation analysis demonstrated that lateralization biases in individuals with normal hearing could not be explained by loudness perception imbalance or hearing threshold asymmetry within the clinical criteria. In conclusion, ILD lateralization biases exhibited by individuals with normal symmetrical hearing may be attributed to subclinical asymmetries that are not detectable through conventional audiometry or psychophysical loudness perception assessments.