PERCEPTION OF SPEECH IN THE PRESENCE OF COMPETING VOICES

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The proposed research has three overall objectives: first, to investigate the acoustic properties which enable listeners with normal hearing to separate speech from competing sounds, including other voices; second, to study the perceptual strategies used by listeners to extract these properties from the composite waveform; and third, to develop and evaluate a model of speech-source segregation. Individuals suffering from hearing impairment of cochlear origin often report difficulties in understanding speech when competing voices are present. Research on the perceptual processes involved in separating speech from other sounds may provide insights into the difficulties faced by hearing-impaired listeners,-and may suggest forms of signal processing to enhance the intelligibility of speech signals corrupted by background noise and thereby improve the design of future signal-processing hearing aids. The experimental component of the project will investigate the role of voice fundamental frequency (f 0) and formant frequencies in the perceptual segregation of competing voices. In one set of experiments, listeners will attend to a mixture of two synthesized "Voices" and identify what each of them is saying. The contribution to voice separation of f 0 differences, f, changes over time, and formant frequency changes over time will be assessed in terms of the accuracy of identification performance. A second set of experiments will use a matching paradigm to examine the link between pitch perception and voice segregation. A third set will use a vowel-matching task to examine the perceptual consequences of formant overlap, which frequently exists when voices compete. The modeling component of the project involves the further development and evaluation of a computational model of the auditory and perceptual processes underlying the performance of listeners in tasks involving two competing voices (Assmann and Summerfield, 1990). New development& will include the introduction of a sliding time analysis window to accommodate changing f o's and changing formant patterns, and an elaborated segregation procedure which reflects the findings of the perceptual experiments.