ASYNCHRONOUS INTERLEAVED STIMULATION (AIS) - A NEW SPEECH CODING STRATEGY FOR COCHLEAR IMPLANT

Cochlear implants use a fixed or FO dependant stimulation rate, whatev er the sound analysed (vowel or consonant) or procedure (fixed filters or FFT). We present a procedure which varies as a function of the inp ut signal. This method is based on FFT analysis using a variable width analysis window. Short windows are applied on the transient part of t he signal, providing poor frequency resolution but good time resolutio n; they permit us to accurately follow the speech signal in time durin g its fast temporal variations. Large windows are applied on the stati onary parts of the signal, providing better frequency resolution but p oor time resolution. Transient parts of the speech order this window s witching; they are detected using the statistical properties of the FF T; moreover, the narrow windowing is coupled to an increase of the sti mulation frequency. This strategy has been implemented using the DIGIS ONIC cochlear implant software, and clinically assessed in 6 regular c ochlear implant users, on the basis of a consonant-vowel-consonant tes t. This Asynchronous-Interleaved-Stimulation (AIS) strategy provides t he patients with better discrimination than fixed window FFT analysis. The coding protocol will be described and results presented.