Spatial Hearing as a Function of Presentation Level in Moderate-to-Severe Unilateral Conductive Hearing Loss.

Hypothesis: Patients with moderate-to-severe unilateral conductive hearing loss (UCHL) can make use of binaural difference cues when stimuli are presented at a high enough intensity to provide audibility in the affected ear.
Background: Spatial hearing is essential for listening in complex environments and sound source localization. Patients with UCHL have decreased access to binaural difference cues, resulting in poorer spatial hearing abilities compared with listeners with normal hearing.
Methods: Twelve patients with moderate-to-severe UCHL, most due to atresia (83.3%), and 12 age-matched controls with normal hearing bilaterally participated in this study. Outcome measures included: 1) spatial release from masking, and 2) sound source localization. Speech reception thresholds were measured with target speech (Pediatric AzBio sentences) presented at 0 degree and a two-talker masker that was either colocated with the target (0 degree) or spatially separated from the target (symmetrical, ±90 degrees). Spatial release from masking was quantified as the difference between speech reception thresholds in these two conditions. Localization ability in the horizontal plane was assessed in a 180 degree arc of 11 evenly-spaced loudspeakers. These two tasks were completed at 50 and 75 dB SPL.
Results: Both children and adults with UCHL performed more poorly than controls when recognizing speech in a spatially separated masker or localizing sound; however, this group difference was larger at 50 than 75 dB SPL.
Conclusion: Patients with UCHL experience improved spatial hearing with the higher presentation level, suggesting that the auditory deprivation associated with a moderate-to-severe UCHL does not preclude exposure to-or use of-binaural difference cues.