Roles of speech errors, monitoring, and anticipation in the production of normal and stuttered disfluencies
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Date
23/11/2011Author
Brocklehurst, Paul Harrison
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Abstract
In their Covert Repair Hypothesis (CRH), Postma and Kolk (1993) proposed that
stuttering-like disfluencies arise, in both normal and stuttered speech, as a consequence of
speakers‟ attempts to repair phonological-encoding errors before they start to speak. They
posited that stutterers are particularly disfluent because they make larger numbers of such
errors compared to normally-fluent speakers. To date, however, experimental research has
provided little reliable evidence to support or counter this hypothesis. This thesis constitutes
a systematic attempt to provide such evidence. Using a tongue-twister paradigm in
conjunction with manipulations of auditory masking, it first documents (a) the vigilance with
which normally-fluent speakers monitor for such errors; (b) the relative accuracy with which
they detect them; and (c) the frequency with which they occur – in both inner and overt
speech. A second set of experiments then extends the same investigation to a group of
stutterers and matched controls and explores the relationship between the occurrence of
participants‟ errors in the experimental paradigm and the frequency of their stuttering-like
disfluencies in everyday speaking situations. Together, these experiments reveal that,
compared to controls, participants who stutter monitor their speech with similar levels of
vigilance; identify phonemic errors with similar degrees of accuracy; and, as predicted by the
CRH, produce significantly more errors – in both their inner and overt speech. However,
contrary to the predictions of the CRH, no relationship was found between the frequency of
such errors in inner speech and the severity of participants‟ disfluencies. In a final set of
experiments, a speech-recognition paradigm is employed to explore an alternative
hypothesis: that stuttering-like disfluencies can be precipitated, in a speaker, by the mere
anticipation that his words will result in communication failure. Results revealed that, for
stutterers, stuttering decreased on words that were consistently followed by feedback
implying correct recognition, but not on words followed by feedback implying incorrect
recognition. For normally-fluent speakers, equivalent correlations were not found. The thesis concludes that slow or impaired phonological encoding may play a role in the development
of the disorder. But, once established, the anticipation of communication failure may be a
more important factor in determining where and when stuttering-like disfluencies actually
occur. It then discusses implications of the experimental findings for hypotheses that posit a
connection between phonological encoding and stuttering.