Investigation of the effect of cochlear implant electrode length on speech comprehension in quiet and noise compared with the results with users of electro-acoustic-stimulation, a retrospective analysis

OBJECTIVES: This 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. METHODES: 91 adults with some degree of residual hearing were implanted with a FLEX(20), FLEX(24), or FLEX(28) 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. RESULTS: While the FLEX(20) ES and FLEX(24) ES groups were still in their learning phase between the 3 to 6 months interval, the FLEX(28) ES group was already reaching a performance plateau at the three months appointment yielding remarkably high test scores. EAS subjects using FLEX(20) or FLEX(24) electrodes outscored ES-only subjects with the same short electrodes on all 3 tests at each interval, reaching significance with FLEX(20) ES and FLEX(24) 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, FLEX(28) ES subjects significantly outscored FLEX(20) ES subjects on all 3 tests and the FLEX(24) ES subjects on 2 tests. At the-6 months interval, FLEX(28) ES subjects still exceeded the other ES-only subjects although the difference did not reach significance. CONCLUSIONS: Among ES-only users, the FLEX(28) 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.