Clinical design and evaluation of the prototype of a new digital audioprosthesis for profound hearing loss: speech recognition aspects.

The design and implementation of the prototype of a digital hearing aid and its computerized fitting interface, followed by a basic preliminary clinical evaluation concerning speech recognition aspects, is reported. The final device is particularly destined to those patients suffering sensorineural hearing losses with recruitment and problems for speech recognition. The prototype is based on the digital signal processor TMS320C30. The host is a personal computer. The primary concept of the processing strategy is the 'integral treatment of acoustic information' within the remaining auditory field of the patient leading to minimum modification of the signal profile. The processing stages include linear amplification, specially designed AD conversion, real fast Fourier transform, 128 multiband single treatment (compression threshold and magnitude of compression), inverse fast Fourier transform, and DA conversion. Compression parameters and pure-tone audiometry data are entered by the computerized fitting interface which also provides real time information of input and output spectral profile. The preliminary clinical evaluation here reported corresponds to a series of 13 patients and it is focused on speech recognition performances. Ten patients had sensorineural hearing loss. Three subjects served as controls. All subjects were studied by an extensive audiological protocol. In 6 patients the prototype improved the maximum intelligibility with respect to unaided hearing reaching levels in the range of 90-100%. In 4 patients using conventional hearing aids, the prototype improved the maximum intelligibility with respect to the previous aided hearing. Values reached the same range as in the former 6 patients. Straightening of the speech audiometry curves was observed in those patients with recruitment. Two controls with previously normal speech recognition showed no worsening and others with conductive deafness reported additional improvement of the responses in noisy conditions with respect to the audioprosthesis in use.