The effect of fundamental frequency on the intelligibility of speech with flattened intonation contours

Purpose: To examine the effect of fundamental frequency (F0) on the intelligibility of speech with flattened F0 contours in noise. Method: Participants listened to sentences produced by 2 female talkers in white noise. The listening conditions included the unmodified original sentences and sentences with resynthesized F0 that reflected the average low F0, the median F0, and the average high F0 of each talker's productions. Results: The sentences with flattened F0 contours yielded poorer intelligibility than the unmodified ones, but the sentences with flattened F0 did not produce equivalent performance. The sentences with F0 contours flattened at the average low F0 yielded better performance than sentences at the median F0. The sentences with F0 flattened at the average high F0 yielded poorer performance than the sentences flattened at the median F0. Conclusions: F0 height accounted for only a small amount of the drop in speech understanding in speech with a flattened F0 in healthy talkers. Although this study used healthy talkers, the findings suggest that clinicians should focus on having clients produce speech with naturally varying F0; F0 height is a secondary factor in the drop in intelligibility seen in monotone speech for female talkers.