no. PTA-030-2002-01229Natural spoken language is full of disfluency. Around 10% of utterances produced
in everyday speech contain disfluencies such as repetitions, repairs, filled pauses
and other hesitation phenomena. The production of disfluency has generally been
attributed to underlying problems in the planning and formulation of upcoming
speech. However, it remains an open question to what extent factors known to
affect the selection and retrieval of words in isolation influence disfluency production
during connected speech, and whether different types of disfluency are associated
with difficulties at different stages of production.
Previous attempts to answer these questions have largely relied on corpora of unconstrained,
spontaneous speech; to date, there has been little direct experimental
research that has attempted to manipulate factors that underlie natural disfluency
production. This thesis takes a different approach to the study of disfluency production
by constraining the likely content and complexity of speakers utterances
while maintaining a context of naturalistic, spontaneous speech.
This thesis presents evidence from five experiments based on the Network Task
(Oomen & Postma, 2001), in addition to two related picture-naming studies. In
the Network Task, participants described to a listener the route of a marker as it
traverses a visually presented network of pictures connected by one or more paths.
The disfluencies of interest in their descriptions were associated with the production
of the picture name. The experiments varied the ease with which pictures in
the networks could be named by manipulating factors known to affect lexical or
pre-lexical processing: lexical access and retrieval were impacted by manipulations of picture-name agreement and the frequency of the dominant picture names, while
visual and conceptual processing difficulty was manipulated by blurring pictures
and through prior picture familiarisation. The results of these studies indicate that
while general production difficulty does reliably increase the likelihood of disfluency,
difficulties associated with particular aspects of lexical access and retrieval
have dissociable effects on the likelihood of disfluency. Most notably, while the production
of function word prolongations demonstrates a close relationship to lexical
difficulties relating to the selection and retrieval of picture names, filled pauses tend
to occur predominantly at the beginning of utterances, and appear to be primarily
associated with message-level planning processes. Picture naming latencies correlated
highly with the rates of observed hesitations, establishing that the likelihood
of a disfluency could be attributed to the same lexical and pre-lexical processes that
result in longer naming times. Moreover, acoustic analyses of a subset of observed
disfluencies established that those disfluencies associated with more serious planning
difficulties also tended to have longer durations, however they do not reliably
relate to longer upcoming delays.
Taken together, the results of these studies demonstrate that the elicitation of
disfluency is open to explicit manipulation, and that mid-utterance disfluencies
are related to difficulties during specific production processes. Moreover, the type
of disfluency produced is not arbitrary, but may be related to both the type and
location of the problem encountered at the point that speech is suspended. Through
the further exploration of these relationships, it may be possible to use disfluency
as an effective tool to study online language production processes