Speech recognition and acoustic features in combined electric and acoustic stimulation.

Objective: In this study, the authors aimed to identify speech information processed by a hearing aid (HA) that is additive to information processed by a cochlear implant (CI) as a function of signal-to-noise ratio (SNR).

Methods: Speech recognition was measured with CI alone, HA alone, and CI + HA. Ten participants were separated into 2 groups; good (aided pure-tone average [PTA] < 55 dB) and poor (aided PTA ≥ 55 dB) at audiometric frequencies ≤ 1 kHz in HA.

Results: Results showed that the good-aided PTA group derived a clear bimodal benefit (performance difference between CI + HA and CI alone) for vowel and sentence recognition in noise, whereas the poor-aided PTA group received little benefit across speech tests and SNRs. Results also showed that a better aided PTA helped in processing cues embedded in both low and high frequencies; none of these cues was significantly perceived by the poor-aided PTA group.

Conclusions: The aided PTA is an important indicator for bimodal advantage in speech perception. The lack of bimodal benefits in the poor group may be attributed to the nonoptimal HA fitting. Bimodal listening provides a synergistic effect for cues in both low- and high-frequency components in speech.