Speechreading supplemented with formant-frequency information from voiced speech.

The benefit of supplementing speechreading with information about the frequencies of the first and second formants from the voiced sections of the speech signal was studied by presenting short sentences to 18 normal-hearing listeners under the following three conditions: (a) speechreading combined with listening to the formant-frequency information, (b) speechreading only, and (c) formant-frequency information only. The formant frequencies were presented either as pure tones or as a complex speechlike signal, obtained by filtering a periodic pulse sequence of 250 Hz by a cascade of four second-order bandpass filters (with constant bandwidth); the center frequencies of two of these filters followed the frequencies of the first and second formants, whereas the frequencies of the others remained constant. The percentage of correctly identified syllables increased from 22.8 in the case of speechreading only to 82.0 in the case of speechreading while listening to the complex speechlike signal. Listening to the formant information only scored 33.2% correct. However, comparison with the best-scoring condition of our previous study [Breeuwer and Plomp, J. Acoust. Soc. Am. 76, 686-691 (1984)] indicates that information about the sound-pressure levels in two one-octave filter bands with center frequencies of 500 and 3160 Hz is a more effective supplement to speechreading than the formant-frequency information.