|dc.description.abstract||Everyday speech is littered with disfluencies such as filled pauses, silent pauses,
repetitions and repairs which reflect a speaker’s language production difficulties.
But what are the effects on language comprehension?
This thesis took a novel approach to the study of disfluencies by combining an
investigation of the immediate effects on language processing with an investigation
of the longer-term effects for the representation of language in memory. A series of
experiments is reported which reflects the first attempt at a systematic investigation
of the effects of different types of disfluencies on language comprehension.
The experiments focused on the effects of three types of disfluencies—ers, silent
pauses, and repetitions—on the comprehension of subsequent words. Critical words
were either straightforward continuations of the pre-interrupted speech or a repair
word which corrected the pre-interrupted speech. In addition, the effects that occur
when er, repetition, and repair disfluencies themselves are processed, were assessed.
ERPs showed that the N400 effect elicited in response to contextually unpredictable
compared to predictable words was attenuated by the presence of a pre-target er
reflecting a reduction in the standard difference where unpredictable words are more
difficult to integrate into their contexts. This finding suggests that ers may reduce
the extent to which listeners make predictions about upcoming words. In addition, words preceded by an er were more likely to be correctly recognised in a subsequent
memory test. These findings demonstrate a longer-term consequence for representation
which may reflect heightened attention during processing. Silent pauses did not
affect the N400 but there was some indication of an effect on recognition memory.
Repetition disfluencies did not affect the N400 or recognition memory. These findings
demonstrate the importance of the nature of the disruption to speech. For all
types of disfluent utterances, unpredictable words elicited a Late Positive Complex
(LPC), possibly reflecting processes associated with memory retrieval and control
as listeners attempted to resume structural fluency after any interruption.
Ers themselves elicited standard attention-related ERP effects: the Mismatch Negativity
(MMN) and P300 effects, supporting the possibility that ers heighten attention.
Repetition disfluencies elicited a right posterior positivity, reflecting detection
of the disfluency and possibly syntactic reanalysis. Repair disfluencies elicited an
early frontal negativity, possibly related to the detection of a word category violation,
and a P600 effect, reflecting syntactic reanalysis. The presence of an er
preceding the repair eliminated the early negativity, but had no effect on the P600
suggesting that ers may prepare listeners for the possibility of an upcoming repair,
but that they do not reduce the difficulty associated with reanalysis.
Taken together, the results from the studies reported in the thesis support an account
of disfluency processing which incorporates both prediction and attention||en