Emergence of Binaural Summation After Surgical Correction of Unilateral Congenital Aural Atresia

Objective: To investigate the emergence of binaural summation in patients with unilateral congenital aural atresia undergoing surgical correction. Study Design: Preoperative and postoperative audiometric testing in a prospective cohort of 10 patients with unilateral congenital aural atresia. Setting: University-based tertiary care center. Patients: Ten patients (ages 6-53) with an average 69 dB (+/- 9 dB sd) unilateral conductive hearing loss, normal hearing in the nonatretic ear, and normal bone conduction in the atretic ear. Interventions: Pre- and postoperative hearing in noise test in quiet and in noise. Main Outcome Measures: Levels of sentences presented from a single central speaker were adaptively varied to determine a speech reception threshold (SRT), first in quiet and then with simultaneous multitalker babble at 65 dB SPL from the same speaker. Results: Preoperative SRT was worse than normal controls in both quiet (p = 0.001) and in noise (p = 0.05), as expected. Postoperative SRT in quiet improved 3.5 dB (marginally significant with one-tailed p value of 0.05); thresholds in noise improved an insignificant 0.8 dB (one-tailed p = 0.2). Converting results to dB-worse-than normal, atresia patients did better in noise (relative to normal) than in quiet (p = 0.008). Conclusion: The expected summation effect (3 dB) occurs after atresia surgery in quiet but not in noise. Relative to normal, these patients performed better in noise than quiet, perhaps because these patients develop skills attending to threshold-level speech in noise during their years without binaural benefit.