Early Fitting in Cochlear Implantation: Benefits and Limits.

OBJECTIVE: Evaluation of a shortened delay time between surgical placement of the cochlear implant (CI) device and processor activation to less than 8 days (early CI fitting). Assessment of benefits and limits of early fitting in terms of medical, technical, audiological, and subjective outcome. STUDY DESIGN: Prospective. SETTING: Tertiary referral center. PATIENTS: Forty-one patients scheduled for cochlear implant surgery divided into early fit (EF, n = 21) and control group (CG, n = 19). MAIN OUTCOME MEASURES: Questionnaires were used to evaluate technical, medical, and subjective outcomes associated with early fitting. Additional, electrode impedance and speech recognition scores were measured. These data, collected preoperative, at first activation and after 3 months were compared with the CG with standard fitting. RESULTS: The medical and audiological status of the EF subjects allowed early fitting in nearly all patients (20/21). Evidence of pain, delayed wound healing, or other compromises was equal in both study groups. Speech recognition scores show comparable development over time for EF and CG. Average electrode impedance was significantly higher in the CG at first activation. CONCLUSIONS: Early fitting of the sound processor is feasible and did not compromise wound healing or generates additional pain. During the first month following surgery, reduction of wound swelling can be expected. Hence, regular inspection of magnet strength is recommended at follow-ups. Over all, early activation of their CI device was highly appreciated by nearly all patients.

Binaural integration of periodically alternating speech following cochlear implantation in subjects with profound sensorineural unilateral hearing loss.

In cochlear implant (CI) recipients with unilateral hearing loss (UHL) and normal hearing (NH) in the contralateral ear, the central auditory system receives signals of different auditory modalities, i.e. electrically via the CI ear as well as acoustically via the NH ear. The present study investigates binaural integration of bimodal stimulation in the central auditory system of 10 CI subjects with UHL by applying a modified version of the Rapidly Alternating Speech Perception (RASP) test to characterise speech recognition ability under monotic and dichotic listening arrangements. Subsequently, the results for each monotic and dichotic test condition were compared to quantify the binaural benefit from CI usage. The study results demonstrate significantly improved speech recognition under dichotic compared to monotic listening conditions, providing evidence that there is binaural integration of acoustically and electrically transmitted speech segments in the central nervous system at brainstem and cortical levels. In contrast to more commonly used tests of binaural integration, such as localisation, the RASP test provides the clinical option to investigate binaural integration involving structures at the cortical level.

Auditory streaming by phase relations between components of harmonic complexes: a comparative study of human subjects and bird forebrain neurons.

Auditory streaming describes a percept in which a sequential series of sounds either is segregated into different streams or is integrated into one stream based on differences in their spectral or temporal characteristics. This phenomenon has been analyzed in human subjects (psychophysics) and European starlings (neurophysiology), presenting harmonic complex (HC) stimuli with different phase relations between their frequency components. Such stimuli allow evaluating streaming by temporal cues, as these stimuli only vary in the temporal waveform but have identical amplitude spectra. The present study applied the commonly used ABA- paradigm (van Noorden, 1975) and matched stimulus sets in psychophysics and neurophysiology to evaluate the effects of fundamental frequency (f0), frequency range (f(LowCutoff)), tone duration (TD), and tone repetition time (TRT) on streaming by phase relations of the HC stimuli. By comparing the percept of humans with rate or temporal responses of avian forebrain neurons, a neuronal correlate of perceptual streaming of HC stimuli is described. The differences in the pattern of the neurons' spike rate responses provide for a better explanation for the percept observed in humans than the differences in the temporal responses (i.e., the representation of the periodicity in the timing of the action potentials). Especially for HC stimuli with a short 40-ms duration, the differences in the pattern of the neurons' temporal responses failed to represent the patterns of human perception, whereas the neurons' rate responses showed a good match. These results suggest that differential rate responses are a better predictor for auditory streaming by phase relations than temporal responses.