Sensitivity of bimodal listeners to interaural time differences with modulated single- and multiple-channel stimuli.

In a previous study, it was shown that users of a cochlear implant and a contralateral hearing aid are sensitive to interaural time differences (ITDs). In the current study, we investigated (1) the influence on ITD sensitivity of bilaterally varying the place of excitation in the cochlea and of modulation frequency, and (2) the sensitivity to ITD with a 3-channel stimulus generated using continuous-interleaved-sampling (CIS)-like processing. The stimuli were (1) a high-frequency carrier (acoustic sinusoid and single-electrode electric pulse train), modulated with a half-wave-rectified low-frequency sinusoid (a so-called transposed stimulus), and (2) a 3-channel stimulus, generated by sending an acoustic click train through processing similar to the CIS strategy. Four bimodal listeners were sensitive to ITD for both stimulus types. For the first stimulus type, there was no significant influence on ITD sensitivity of the acoustic carrier frequency. Performance decreased with increasing modulation frequency with a limit of sensitivity at around 150-200 Hz. Sensitivity was similar for the single- and 3-channel stimulus. The results indicate the possibility of ITD perception with adapted clinical processors, which can lead to improved sound source localization and binaural unmasking.