Fundamental frequency information for speech recognition via bimodal stimulation: Cochlear implant in one ear and hearing aid in the other

Objective: The aim of this study was to examine the role of fundamental frequency (F0) information in improving speech perception of individuals with a cochlear implant (CI) who use a contralateral hearing aid (HA). The authors hypothesized that in bilateral-bimodal (CI/HA) users the perception of natural prosody speech would be superior to the perception of speech with monotonic flattened F0 contour, whereas in unilateral CI users the perception of both speech signals would be similar. They also hypothesized that in the CI/HA listening condition the speech perception scores would improve as a function of the magnitude of the difference between the F0 characteristics of the target speech signal and the F0 characteristics of the competitors, whereas in the CI-alone condition such a pattern would not be recognized, or at least not as clearly. Design: Two tests were administered to 29 experienced CI/HA adult users who, regardless of their residual hearing or speech perception abilities, had chosen to continue using an HA in the nonimplanted ear for at least 75% of their waking hours. In the first test, the difference between the perception of speech characterized by natural prosody and speech characterized by monotonic flattened F0 contour was assessed in the presence of babble noise produced by three competing male talkers. In the second test the perception of semantically unpredictable sentences was evaluated in the presence of a competing reversed speech sentence spoken by different single talkers with different F0 characteristics. Each test was carried out under two listening conditions: CI alone and CI/HA. Results: Under both listening conditions, the perception of speech characterized by natural prosody was significantly better than the perception of speech in which monotonic F0 contour was flattened. Differences between the scores for natural prosody and for monotonic flattened F0 speech contour were significantly greater, however, in the CI/HA condition than with CI alone. In the second test, the overall scores for perception of semantically unpredictable sentences in the presence of all competitors were higher in the CI/HA condition in the presence of all competitors. In both listening conditions, scores increased significantly with increasing difference between the F0 characteristics of the target speech signal and the F0 characteristics of the competitor. Conclusions: The higher scores obtained in the CI/HA condition than with CI alone in both of the task-specific tests suggested that the use of a contralateral HA provides improved low-frequency information, resulting in better performance by the CI/HA users.