People who have experienced traumatic brain injury (TBI) often report increased
difficulty processing speech than they experienced before their injuries; and this
difficulty is not always accompanied by impaired performance on standardized tests of
language, auditory processing, or other cognitive factors. Unfortunately, there is a paucity
of research directly addressing this issue. Prior studies have mostly focused on measures
of characteristics such as attention (e.g. Schmitter-Edgecombe & Nissley, 2000), dichotic
listening (e.g. Meyers, Roberts, Bayless, Volkert, & Evitts, 2002), and masking release
(e.g. Krause, Nelson, & Kennedy, 2009) in people with TBI. All of these factors may
play their part in functional listening tasks, but separately they cannot capture the
complex task of speech processing (e.g. Wilson 2003). The goal of this dissertation is to
build on existing work to explore and compare the issue of speech processing after brain
injury across several levels: sentence repetition with single-talker interference, using
targets spoken by native- and non-native-accented speakers of English; standardized
testing of cognition and auditory processing; and semi-structured interviews about participants’ subjective experiences with complex speech processing.
This study comprised two experiments. The purpose of Experiment 1 was to
demonstrate the effects of simulated peripheral hearing loss on performance on the
sentence repetition task. Participants in Experiment 1 were 30 healthy young adults, 15 of
whom completed the sentence repetition task with stimuli that were filtered with a 1400
Hz low-pass filter to simulate peripheral hearing loss. The other 15 participants completed the task with unfiltered stimuli. The purpose of Experiment 2 was to compare adults with and without TBI on the (unfiltered) sentence repetition task, and included 13
people in each participant group. Groups were matched for age, education, and estimated
verbal IQ within each experiment. Dependent variables for the sentence repetition task
were accuracy and subjective effort. Participants in Experiment 2 also completed a
battery of standardized tests and a semi-structured interview about their subjective
experiences with speech processing.
Results of Experiment 1 showed that the filtered group was less accurate and
reported greater effort than the unfiltered group, and the filtered group showed greater
effects of speaker accent. Results of Experiment 2 demonstrated that the TBI group had
poorer accuracy than controls, but not significantly higher effort. As predicted, the TBI
group also reported more subjective difficulty with complex speech processing than
healthy controls, but there was no direct correlation between interview reports and
accuracy on the sentence repetition task. Comparisons between the TBI group of
Experiment 2 and the filtered group of Experiment 1 suggest that, although the TBI group did show impaired performance on the speech processing task, their performance was not
consistent with the peripheral auditory effects that were modeled in Experiment 1. This
suggests that the speech processing difficulty experienced by people with TBI cannot be
explained by bottom-up processing (e.g. energetic masking) alone.
Further research is needed in order to better understand the nature of speech
processing problems after TBI, the ultimate goal of which is to be able to develop therapies and strategies that will allow people with TBI to communicate successfully
even in difficult circumstances.
University of Minnesota Ph.D. dissertation. August 2011. Major: Speech-Language-Hearing Sciences. Advisor: Mary R.T. Kennedy. 1 computer file (PDF); xii, 212 pages, appendices 1-7.
Krause, Miriam Ottilie.
The effects of brain injury and talker characteristics on speech processing in a single-talker interference task..
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