Objective: To assess auditory localization accuracy and speech reception threshold (SRT) in complex noise conditions in adult patients with acquired single-sided deafness, after intervention with a cochlear implant (CI) in the deaf ear.

Study design: Nonrandomized, open, prospective patient series.

Setting: Tertiary referral university hospital.

Patients: Eleven patients with late-onset single-sided deafness (SSD) and normal hearing in the unaffected ear, who received a CI. All patients were experienced CI users.

Intervention: Unilateral cochlear implantation.

Main outcome measures: Speech perception was tested in a complex multitalker equivalent noise field consisting of multiple sound sources. Speech reception thresholds in noise were determined in aided (with CI) and unaided conditions. Localization accuracy was assessed in complete darkness. Acoustic stimuli were radiated by multiple loudspeakers distributed in the frontal horizontal plane between -60 and +60 degrees.

Results: In the aided condition, results show slightly improved speech reception scores compared with the unaided condition in most of the patients. For 8 of the 11 subjects, SRT was improved between 0.37 and 1.70 dB. Three of the 11 subjects showed deteriorations between 1.22 and 3.24 dB SRT. Median localization error decreased significantly by 12.9 degrees compared with the unaided condition.

Conclusion: CI in single-sided deafness is an effective treatment to improve the auditory localization accuracy. Speech reception in complex noise conditions is improved to a lesser extent in 73% of the participating CI SSD patients. However, the absence of true binaural interaction effects (summation, squelch) impedes further improvements. The development of speech processing strategies that respect binaural interaction seems to be mandatory to advance speech perception in demanding listening situations in SSD patients.