Role of F0 in speech reception in the presence of interference : simulating aspects of cochlear-implant processing

Abstract

Speech is perhaps the most ecologically important acoustic stimulus to human beings, because it remains the primary means by which people interact socially. Despite many significant advances made in the development of cochlear implants, even the most successful cochlear-implant users do not hear as well as normal-hearing listeners. The differences in performance between normal-hearing listeners and cochlear-implant users are especially pronounced in understanding speech in complex auditory environments. For normal-hearing listeners, voice pitch or the fundamental frequency (FO) of voicing has long been thought to play an important role in the perceptual segregation of speech sources. The aim of this dissertation was to examine the role of voice pitch in speech perception in the presence of background interference, specifically simulating aspects of envelope-vocoder style implant processing. The findings of the studies show that FO encoded via envelope periodicity does not provide a sufficiently salient cue for the segregation of speech. This suggests that the poor speech reception performance of implant users in background interference may, at least in part, be due to the lack of salient voice pitch cues. When low-frequency fine-structure information was added to envelope- vocoder processed high-frequency information, some FO segregation benefits returned and the reception of speech in complex backgrounds improved. Taken as a whole, the dissertation suggests that low frequency fine-structure information is important to the task of speech segregation, and that every effort should be made to present such information to cochlear-implant users.