Effect of Frequency Compression on Spatial Release from Masking in Individuals with Normal Hearing and Hearing Impairment

Abstract

Nonlinear frequency compression (NLFC) is a hearing aid processing strategy designed to improve audibility of high-frequency sounds, but it may alter spatial hearing cues. This study investigated the impact of nonlinear frequency compression (NLFC) on spatial release from masking (SRM) in individuals with normal hearing and those with bilateral moderate sensorineural hearing loss. A total of 40 participants (20 normal-hearing young adults and 20 older adults with hearing impairment) completed a sentence recognition task in multitalker babble under varying NLFC conditions including no activation, unilateral, and bilateral activation across different signal-to-noise ratios. The stimuli were spatially presented in collocated (0˚) and separated (37.5˚) conditions to compute SRM. Findings revealed that while NLFC may enhance SRM under challenging listening conditions, this effect in normal-hearing individuals was largely attributable to degraded performance in the collocated condition rather than genuine spatial enhancement. More critically, unilateral NLFC significantly disrupted spatial cues in the hearing-impaired group, resulting in reduced SRM compared to bilateral or no activation conditions. This suggests that asymmetrical processing may impair interaural coherence, thereby diminishing spatial benefit. The study highlights the importance of maintaining bilateral processing consistency in hearing aid fittings and cautions against the use of unilateral NLFC, particularly in cases where spatial hearing is functionally important.