Speech Perception With Novel Stimulation Strategies for CombinedCochleo-Vestibular Systems.

Cochlear implants are very well established in the rehabilitation of hearing loss and are regarded as the most successful neuroprostheses to date. While a lot of progress has also been made in the neighboring field of specific vestibular implants, some diseases affect the entire inner ear, leading to both hearing and vestibular hypo- or dysfunction. The proximity of the cochlear and vestibular organs suggests a single combined implant as a means to alleviate the associated impairments. While both organs can be stimulated in a similar way with electric pulses applied through implanted electrodes, the typical phase durations needed in the vestibular system seem to be substantially larger than those typically needed in the cochlear system. Therefore, when using sequential stimulation in a combined implant, the pulse stream to the cochlea is interrupted by comparatively large gaps in which vestibular stimulation can occur. We investigate the impact of these gaps in the auditory stream on speech perception. Specifically, we compare a number of stimulation strategies with different gap lengths and distributions and evaluate whether it is feasible to use them without having a noticeable decline in perception and quality of speech. This is a prerequisite for any practicable stimulation strategy of a combined system and can be investigated even in recipients of a normal cochlear implant. Our results show that there is no significant deterioration in speech perception for the different strategies examined in this paper, leaving the strategies as viable candidates for prospective combined cochleo-vestibular implants.

Development of a Mandarin tone identification test: sensitivity index d' as a performance measure for individual tones.

OBJECTIVE: The aim of this study was to develop comprehensive test material for Mandarin tone identification in noise for a male and a female talker. Additionally, the sensitivity index d' as a measure for the listeners' performance to identify individual tones was evaluated. DESIGN: The study followed a prospective design. STUDY SAMPLE: The complete material comprises 72 loudness-balanced syllables in all 4 Mandarin tones. For a selection of 20 syllables, i.e. 80 test words, performance-versus-intensity functions were measured in spectrally matched noise for 16 normal-hearing participants. RESULTS: The average speech reception thresholds in noise were -12.9 dB for the male and -13.6 dB for the female talker recordings. The corresponding slopes were 8.6%/dB and 7.3%/dB. As a performance measure for individual tones, the proportion of correct responses to specific tones was substantially contaminated by response bias. The sensitivity index d', calculated according to detection theory, provided reasonable and unbiased performance versus intensity functions. CONCLUSIONS: The results firstly indicate that the material is homogenous enough for use as a speech test in clinical work and research. Secondly, to assess the discrimination performance for individual tones, d' values outperform the simple proportion of correct responses.

Simultaneous intracochlear stimulation based on channel interaction compensation: analysis and first results.

A simultaneous paradigm for electric stimulation of the acoustic nerve based on a monopolar electrode configuration and sign-correlated pulses is presented. Simultaneous pulse amplitudes are determined by taking into account parameters of spatial channel interaction. The computation of simultaneous amplitudes requires the solution of linear systems of equations in an iterative procedure. The computation amount can be reduced significantly, if the spatial impulse responses in individual electrodes can be approximated by two exponentially decaying branches with decay constants alpha toward apex and beta toward base. Generally, the associated inverse of the channel interaction matrix is tridiagonal. Preliminary vowel and consonant identification tests with four cochlear implant patients have been conducted for sequential and simultaneous processor settings. For equal overall pulse repetition rates, comparable speech perception scores were obtained, when the decay constants alpha and beta were set accordingly. Theoretically, the pulse rate of an N-channel system can be increased up to a factor of N as compared to the standard sequential paradigm, and pulses with technically reasonable phase durations can be utilized.