Speech performance and sound localization in a complex noisy environment in bilaterally implanted adult patients

To evaluate speech performance, in quiet and noise, and localization ability in adult patients who had undergone bilateral and simultaneous implantation.

Prospective multi-center study.

Twenty-seven adult patients with profound or total hearing loss were bilaterally implanted in a single-stage procedure, and simultaneously activated (Med-El, Combi 40/40+). Subjects were assessed before implantation and at 3, 6 and 12 months after switch-on. Speech perception tests in monaural and binaural conditions were performed in quiet and in noise using disyllabic words, with speech coming from the front and a cocktail party background noise coming from 5 loudspeakers. Sound localization measurements were also performed in background noise coming from 5 loudspeakers positioned from -90 degrees to +90 degrees azimuth in the horizontal plane, and using a speech stimulus.

There was a bilateral advantage at 12 months in quiet (77 +/- 5.0% in bilateral condition, 67 +/- 5.3% for the better ear, p < 0.005) and in noise (signal-to-noise ratio +15 dB: 63 +/- 5.9% in bilateral condition, 55 +/- 6.9% for the better ear, p < 0.05). Considering unilateral speech scores recorded in quiet at 12 months, subjects were categorized as 'good performers' (speech comprehension score > or =60% for the better ear, n = 19) and 'poor performers' (n = 8). Subjects were also categorized as 'asymmetrical' (difference between their 2 unilateral speech scores > or =20%, n = 11) or 'symmetrical' (n = 16). The largest advantage (bilateral compared to the better ear) was obtained in poor performers: +19% compared to +7% in good performers (p < 0.05). In the group of good performers, there was a bilateral advantage only in cases of symmetrical results between the 2 ears (n = 10). In the group of poor performers, the bilateral advantage was shown in both patients with symmetrical (n = 6) and asymmetrical results (n = 2). In bilateral conditions, the sound localization ability in noise was improved compared to monaural conditions in patients with symmetrical and asymmetrical performance between the 2 ears. No preoperative factor (age, duration of deafness, use of hearing aids, etiology, etc.) could predict the asymmetrical performance, nor which ear would be the best.

This study demonstrates a bilateral advantage (at 12 months after the implantation) in speech intelligibility and sound localization in a complex noisy environment. In quiet, this bilateral advantage is shown in cases of poor performance of both ears, and in cases of good performance with symmetrical results between the 2 ears. No preoperative factor can predict the best candidates for a simultaneous bilateral implantation.