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Startling auditory stimulus as a window into speech motor planning Chiu, Cheng-hao

Abstract

While speech planning has long been a topic of discussion in the literature, the specific content of speech plans has remained largely conjectural. The present dissertation brings to this problem a methodology using startling auditory stimulus (SAS) to examine the contents of prepared movement plans unaltered by feedback regulation. The startling auditory stimulus (SAS, > 120dB) has been found to elicit rapid release of prepared movements with high accuracy and largely unaltered EMG muscle activity patterns. Because the response latency of these SAS-triggered movements is too short to allow for feedback or correction processes, the executed movements have been used to reveal the contents of the movement plans with little or no feedback information influencing the prepared motor behaviours. In the present dissertation, the first experiment applied this methodology to CV syllable production to test whether English CV syllables can be elicited in the same manner as other limb movements. Results show that a SAS can trigger an early release of a well-formed prepared English CV syllable, including intact lip kinematics and vowel formants. The second experiment investigated whether the observed short latency and additional lip compression are speech-specific or generic to any oral movement. Results show that while prepared speech-like and non-speech movements are subject to early release by SAS, lip compression does not occur as frequently as it does in Spoken speech, suggesting that this preparatory compression may be speech-specific, likely relating to aerodynamic factors. The third experiment further tests whether lip compression that is independent of aerodynamic factors is observed in all speech-related tasks and is elicited at a short latency by SAS. Results show that comparable lip compression resulting from movement overshoot was observed for both Spoken and Mouthed speech. The fourth experiment looked into the level of suprasegmental gestures in speech planning. The results show that while both pitch contour and formants were maintained in the SAS-induced responses, pitch levels were compromised, suggesting that a prepared syllable ought minimally to include phonemic contrasts. SAS provides a useful tool for observing the contents of speech plans.

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Attribution-NonCommercial-NoDerivs 2.5 Canada

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