Spontaneous imitation of fundamental frequency and speech rate by nonstutterers and stutterers

Speech can be described either in terms of acoustics, as a perceptual outcome, or as a motor event. Central to theories of speech perception and production is an attempt to describe how these aspects of speech are interrelated. The present experiment investigated how the nonstutterers' and stutterers' reproductions of acoustically presented interrogative sentences were influenced by experimental variations of intonation (sentence initial vs. sentence final) and speech rate (normal vs. time compressed). We studied the effects of these stimulus manipulations on the speech rate and fundamental frequency (F0) of 10 adult German-speaking nonstutterers and seven stutterers. Experimental manipulations of intonation and speech rate significantly influenced the syllable duration and speech rate of both normal speakers and stutterers. The fundamental frequency of the subjects' responses were also significantly influenced by the intonation of the stimulus. But the stutterers' increase in F0 for stressed syllables was generally less pronounced than that of nonstutterers. These results imply that (a) the subject not only extract linguistic meaning from intonation but that they also store extragrammatical speech rate information, and (b) the speakers adopt these speech rate variations for their own productions. Generally, these results demonstrate that speech perception is not limited to extracting linguistically invariant information. The results show that speakers actively generate their own prosody and that this generative process is influenced by the prosodic structure of another speaker's antecedent speech. The implications of these results for theories of speech production are discussed.