Abstract
Children who experience persistent conductive hearing loss (CHL) early in life often display binaural hearing impairments that persist long after CHL is resolved, suggesting abnormal central auditory development. Abnormal sensitivity to interaural level differences (ILDs) is particularly likely as a CHL (such as an ear infection) can attenuate sound in the affected ear by >30 dB, dramatically distorting ILD cues. Here, we quantified the effects of unilateral CHL on (1) behavioral spatial acuity and (2) neural information processing of ILD cues in the guinea pig auditory midbrain (inferior colliculus, IC) using the mathematical framework of Fisher information (FI). Animals raised with unilateral CHL displayed larger minimum audible angles for high-pass noise compared to age-matched controls, suggesting impaired ILD sensitivity. Based on acoustic directional transfer function measurements, ILD discrimination thresholds were elevated by ~3–6 dB. Following behavior, extracellular recordings were made in the IC contralateral to the previously occluded ear, and ILD discrimination thresholds for single neurons were determined using FI. Across the population, neural ILD discrimination was moderately impaired (~2–3 dB worse-than-control) in CHL animals. Impaired processing of ILD in the IC may in part explain the spatial discrimination deficits observed in animals and children with developmental CHL.