Relationship between auditory function of nonimplanted ears and bimodal benefit

OBJECTIVES:: Patients with a cochlear implant (CI) in one ear and a hearing aid in the other ear commonly achieve the highest speech-understanding scores when they have access to both electrically and acoustically stimulated information. At issue in this study was whether a measure of auditory function in the hearing aided ear would predict the benefit to speech understanding when the information from the aided ear was added to the information from the CI. DESIGN:: The subjects were 22 bimodal listeners with a CI in one ear and low-frequency acoustic hearing in the nonimplanted ear. The subjects were divided into two groups - one with mild-to-moderate low-frequency loss and one with severe-to-profound loss. Measures of auditory function included (1) audiometric thresholds at 750 Hz or lower, (2) speech-understanding scores (words in quiet and sentences in noise), and (3) spectral-modulation detection (SMD) thresholds. In the SMD task, one stimulus was a flat spectrum noise and the other was a noise with sinusoidal modulations at 1.0 peak/octave. RESULTS:: Significant correlations were found among all three measures of auditory function and the benefit to speech understanding when the acoustic and electric stimulation were combined. Benefit was significantly correlated with audiometric thresholds (r = -0.814), acoustic speech understanding (r = 0.635), and SMD thresholds (r = -0.895) in the hearing aided ear. However, only the SMD threshold was significantly correlated with benefit within the group with mild-to-moderate loss (r = -0.828) and within the group with severe-to-profound loss (r = -0.896). CONCLUSIONS:: The SMD threshold at 1 cycle/octave has the potential to provide clinicians with information relevant to the question of whether an ear with low-frequency hearing is likely to add to the intelligibility of speech provided by a CI.