Perception of processed speech by the profoundly hearing impaired

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For many profoundly hearing-impaired speech reading is the most important means of communication; amplified speech may provide, at best, additional information to speech reading. In an attempt to improve audio-visual communication, speech pattern elements that were thought to be most beneficial as a supplement to lip-reading were analyzed. The elements were fundamental frequency (f0), voicing, and the first two formants (F1 and F2). With these elements auditory stimuli were pro-duced with different encodings for voiced speech fragments. In the F1F2 encoding both formants were represented by two adjacent harmonics of f0 around each formant frequency; in the F1 encoding by two harmonics of f0 around F1. In the f0 encoding fundamental frequency was encoded as a single sine wave. In all cases white noise was used during voiceless speech. Out of 20 profoundly hearing-impaired subjects, all subjects but one showed a considerable improvement in lipreading scores when supplemented with an auditory stimulus. In most cases highest scores were obtained with the natural speech condition. For four subjects the F1-encoded signal provided highest scores. Relations among intelligibility scores and dynamic range, gap detection, and difference limen for frequency will be discussed.