The effect of correcting fundamental frequency on the intelligibility of deaf speech and its interaction with temporal aspects.

This study investigates the role of intonation for the intelligibility of deaf speech. The intonation contours of Dutch sentences spoken by deaf children were manipulated using digital signal processing techniques, including LPC analysis. Sentence intonation was corrected by replacing the original F0 contour of the deaf utterance with an artificial contour derived from a formalized intonation grammar. Three types of intonation corrections were produced, differing with respect to the underlying accent structure and the type of F0 movements used. The overall results show that intonation correction yields a small but significant improvement in intelligibility of 7% (from 20% to 27% words correctly identified). The largest gain is obtained after removal of over-accentuations. To evaluate the interaction with temporal aspects, intonation corrections were also implemented on temporally corrected sentences. Total growth in intelligibility due to these combined corrections amounts to 13%. Thus it is concluded that no dramatic gain in intelligibility may be expected if speech pathologists succeed in teaching their deaf pupils to have better control over the suprasegmental aspects of their speech.