Speechreading Enhancement by Voice Fundamental Frequency

The Effects of F_o Contour Distortions

Recognition of words in sentences of known topic was measured in normally hearing adults via speechreading alone and speechreading supplemented with auditory presentation of signals intended to convey variations of voice fundamental frequency (F_o) over time. Three signals were used: (a) the low-pass filtered output of an electroglottograph (unprocessed F_o), (b) a constant amplitude sine wave whose instantaneous frequency was intended to equal that of F_o (processed F_o), and (c) the same sine wave restricted to a small number of discrete frequency steps (quantized F_o). As the number of steps in the quantized F_o contours increased from 1 to 12, the speechreading enhancement effect increased. The quantized F_o contour with 12 steps was as effective as the processed F_o contour (without quantization), but this processed contour was significantly less effective than the unprocessed electroglottograph signal. The results show that the auditory F_o speechreading enhancement effect is sensitive to the errors introduced by the F_o extraction and regeneration process used in this study. It is also sensitive to the quantization of F_o contours into less than 12 steps. Whether more than 12 steps are required for the full enhancement effect remains to be determined.

KEY WORDS: speechreading, voice fundamental frequency, distortions, auditory enhancement

Submitted on August 26, 1991
Accepted on January 24, 1992

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