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For normal-hearing (NH) listeners, interaural information in both temporal envelope and temporal fine structure contribute to binaural unmasking of target signals in background noise; however, in many conditions low-frequency interaural information in temporal fine structure produces greater binaural unmasking. For bilateral cochlear-implant (CI) listeners, interaural information in temporal envelope contributes to binaural unmasking; however, the effect of encoding temporal fine structure information in electrical pulse timing (PT) is not fully understood. In this study, diotic and dichotic signal detection thresholds were measured in CI listeners using bilaterally synchronized single-electrode stimulation for conditions in which the temporal envelope was presented without temporal fine structure encoded (constant-rate pulses) or with temporal fine structure encoded (pulses timed to peaks of the temporal fine structure). CI listeners showed greater binaural unmasking at 125 pps with temporal fine structure encoded than without. There was no significant effect of encoding temporal fine structure at 250 pps. A similar pattern of performance was shown by NH listeners presented with acoustic pulse trains designed to simulate CI stimulation. The results suggest a trade-off across low rates between interaural information obtained from temporal envelope and that obtained from temporal fine structure encoded in PT.

Cochlear implants (CIs) provide children with access to speech information from a young age. Despite bilateral cochlear implantation becoming common, use of spatial cues in free field is smaller than in normal-hearing children. Clinically fit CIs are not synchronized across the ears; thus binaural experiments must utilize research processors that can control binaural cues with precision. Research to date has used single pairs of electrodes, which is insufficient for representing speech. Little is known about how children with bilateral CIs process binaural information with multi-electrode stimulation. Toward the goal of improving binaural unmasking of speech, this study evaluated binaural unmasking with multi- and single-electrode stimulation. Results showed that performance with multi-electrode stimulation was similar to the best performance with single-electrode stimulation. This was similar to the pattern of performance shown by normal-hearing adults when presented an acoustic CI simulation. Diotic and dichotic signal detection thresholds of the children with CIs were similar to those of normal-hearing children listening to a CI simulation. The magnitude of binaural unmasking was not related to whether the children with CIs had good interaural time difference sensitivity. Results support the potential for benefits from binaural hearing and speech unmasking in children with bilateral CIs.

Speech production by children with cochlear implants (CIs) is generally less intelligible and less accurate on a phonemic level than that of normally hearing children. Research has reported that children with CIs produce less acoustic contrast between phonemes than normally hearing children, but these studies have included correct and incorrect productions. The present study compared the extent of contrast between correct productions of /s/ and /∫/ by children with CIs and two comparison groups: (1) normally hearing children of the same chronological age as the children with CIs and (2) normally hearing children with the same duration of auditory experience. Spectral peaks and means were calculated from the frication noise of productions of /s/ and /∫/. Results showed that the children with CIs produced less contrast between /s/ and /∫/ than normally hearing children of the same chronological age and normally hearing children with the same duration of auditory experience due to production of /s/ with spectral peaks and means at lower frequencies. The results indicate that there may be differences between the speech sounds produced by children with CIs and their normally hearing peers even for sounds that adults judge as correct., (© 2011 Acoustical Society of America)