Auditory Neuropathy Spectrum Disorder

A 6-month-old boy born at 28 weeks gestation is referred to audiology after failing newborn screening. Audiological testing shows pure-tone thresholds of 85 dB HL bilaterally, but otoacoustic emissions (OAEs) are robustly present. Auditory brainstem response (ABR) is absent bilaterally. The infant's parents report he does not turn to sound or babble, despite appearing to respond to vibration. The pattern marked **B** in the diagram best describes this infant's audiological profile. Which of the following is the most appropriate next diagnostic step to guide management?

A 3-year-old boy born at 32 weeks gestation with history of severe hyperbilirubinemia (peak 24 mg/dL, requiring exchange transfusion) and neonatal aminoglycoside exposure presents with inconsistent response to speech and poor word recognition (12% at comfortable listening level) despite pure-tone thresholds that would predict better performance. Otoscopy and tympanometry are normal with absent acoustic reflexes. The pattern marked **A** in the diagram—robustly present otoacoustic emissions and cochlear microphonic with absent/grossly abnormal ABR and disproportionately poor speech discrimination—is demonstrated on testing. Which of the following best explains the dissociation between normal outer hair cell function and severely impaired speech perception in this patient?