Current steering and results from novel speech coding strategies.

Objective: Advanced Bionics' cochlear implants have independent current sources that can share stimulation current between 2 contacts (Current Steering). By stimulating 2 adjacent electrodes with different weights, different pitches can be evoked, allowing to increase the number of processing channels.

Study Design: A counterbalanced crossover design was used to compare 3 different current steering implementations to the clinical HiRes strategy.

Setting: The study was a prospective, within-subject, repeated-measure experiment.

Patients: The study group consisted of 8 postlingually deaf subjects with a minimum of 12-month experience in HiRes.

Intervention: The following programs were evaluated: 1) a Fast Fourier Transformation (FFT)-based current steering implementation with 120 stimulation sites; 2) the same current steering implementation but with 16,000 stimulation sites; and 3) a current steering implementation based on a sinusoidal decomposition of the original signal with 16,000 stimulation sites.

Main Outcome Measures: Speech perception tests in quiet and in Comité Consultatif International Télégraphique et Téléphonique (CCITT) noise, as well as with competing talker; an adaptive test of the frequency difference limen; a Quality Assessment Questionnaire.

Results: Current results do not show any improvement in speech perception for a certain current steering strategy compared with HiRes. However, when selecting the optimal current steering strategy, subjects could achieve a significant benefit compared with the clinical HiRes. In addition, the frequency difference limen could be reduced significantly at 1,280 Hz.

Conclusion: Current steering seems to have the potential to improve both understanding in adverse listening situations and frequency resolution. However, the optimal implementation needs further investigation.