Speech processing for hearing aids for moderate bilateral sensorineural hearing loss

Binaural dichotic presentation can be used for reducing the effects of increased temporal and spectral masking associated with sensorineural loss and for improving speech perception by persons with moderate bilateral loss. Speech processing schemes were implemented based on adjustable gain filtering, spectral splitting with perceptually balanced comb filters, temporal splitting with trapezoidal fading and inter-aural switching periods of 20 and 40 ms, and combined splitting with cyclically swept comb filters with cycle times of 20, 40, and 80 ms. Experimental evaluation was carried out through listening tests involving recognition of randomly presented words by hearing impaired subjects, for establishing the effect of processing schemes and parameters. Binaural filtering always resulted in improvement. The maximum number of subjects showed large improvement with spectral splitting. Temporal splitting was better with 20 ms switching, while the combined splitting gave best improvements for cycle time of 40 ms.