ObjectivesThis investigation evaluated the effect of cochlear implant (CI) electrode length on speech comprehension in quiet and noise and compare the results with those of EAS users.Methodes91 adults with some degree of residual hearing were implanted with a FLEX20, FLEX24, or FLEX28 electrode. Some subjects were postoperative electric-acoustic-stimulation (EAS) users; the other subjects were in the groups of electric stimulation-only (ES-only).Speech perception was tested in quiet and noise at 3 and 6 months of ES or EAS use. Speech comprehension results were analyzed and correlated to electrode length.ResultsWhile the FLEX20 ES and FLEX24 ES groups were still in their learning phase between the 3 to 6 months interval, the FLEX28 ES group was already reaching a performance plateau at the three months appointment yielding remarkably high test scores. EAS subjects using FLEX20 or FLEX24 electrodes outscored ES-only subjects with the same short electrodes on all 3 tests at each interval, reaching significance with FLEX20 ES and FLEX24 ES subjects on all 3 tests at the 3-months interval and on 2 tests at the 6- months interval. Amongst ES-only subjects at the 3- months interval, FLEX28 ES subjects significantly outscored FLEX20 ES subjects on all 3 tests and the FLEX24 ES subjects on 2 tests. At the-6 months interval, FLEX28 ES subjects still exceeded the other ES-only subjects although the difference did not reach significance.ConclusionsAmong ES-only users, the FLEX28 ES users had the best speech comprehension scores, at the 3- months appointment and tendentially at the 6 months appointment. EAS users showed significantly better speech comprehension results compared to ES-only users with the same short electrodes.

This study revealed that children implanted before the age of 1 year were subjected to no additional risks and showed superior development of speech understanding. Cochlear implantation should therefore be performed in very young children identified as suffering from profound bilateral hearing loss.

The benefit of combined electric and acoustic hearing in bimodally fitted subjects depends mainly on residual hearing in the low-frequency range below 500 Hz. For bimodal fitting to yield significant benefits, hearing loss in the contralateral ear should not exceed 80 dB HL in the low frequencies.

This study supports the view that pediatric cochlear implantation provides positive cost-benefit ratios compared with hearing aid users, depending on the age at implantation. Implantation is strongly recommended from the payers' perspective for children implanted before the age of 2 years.

Although auditory sensation appeared immediately after device activation, a period of 6 months was necessary for relearning and adaptation of the central auditory system to the altered form of auditory information presented by the auditory brainstem implant.