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Phonetic Competition and Speech Recognition: Effects of Clear Speech in Aphasia

Poster B67 in Poster Session B, Tuesday, October 24, 3:30 - 5:15 pm CEST, Espace Vieux-Port

Kathrin Rothermich1, David Saltzman2, Xin Xie3, Emily Myers2; 1East Carolina University, 2University of Connecticut, 3University of California, Irvine

Neurobiological models of language provide evidence linking comprehension deficits to lesions in the left temporal lobe. However, research suggests that damage to the left frontal brain regions can also result in speech perception impairments, especially when dealing with listening to speech under challenging conditions and when the acoustic signal is phonetically ambiguous. Substantiating these findings, recent fMRI studies have demonstrated the activation of the left inferior frontal gyrus during the resolution of phonetic competition. Additionally, the left superior temporal gyrus has been associated with speech intelligibility or perceived "goodness" of speech. When talkers use “clear speech” modes of communication, they naturally increase the acoustic distinctiveness of phonetic tokens, resulting in expanded vowel space, and more released stop consonants (as well as changes in prosody, rate, and amplitude). As such, clear speech provides a natural test case for examining the effect of naturally occurring variation in phonetic distinctiveness on comprehension. This study aimed to accomplish two goals: (1) to examine the influence of clear speech on speech recognition and (2) to investigate the hypothesis that frontal regions play a crucial role in resolving phonetic competition when the signal is more phonetically ambiguous. Nineteen participants with aphasia and 19 age-matched control participants were included in the study. They listened to sentences presented either in a clear or casual manner of production, where phonetic distinctiveness was greater for the clear manner. Immediately after, participants were presented with a word through headphones and asked to determine if it was part of the previously heard sentence. Accuracy and reaction time served as the dependent variables. Among the control participants, clear speech led to a significant advantage in terms of accuracy percentage, whereas no significant effect was observed for reaction time. These findings indicate that clear sentences resulted in reduced phonetic ambiguity, thereby facilitating the speech recognition task. In individuals with aphasia, the overall accuracy was significantly lower when compared to controls. They also exhibited only a slight benefit from clear speech, although the difference was not statistically significant. No significant effects on reaction time were observed. To summarize, the results suggest that clear speech improves speech recognition accuracy, but people with aphasia may not benefit as greatly from reduced phonetic competition. These findings are discussed in relation to the location of lesions in frontal versus temporal brain regions, the severity of aphasia, and their implications for neurobiological models of language.

Topic Areas: Speech Perception, Disorders: Acquired

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