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published_or_final_version / Speech and Hearing Sciences / Master / Master of Science in Audiology

Dichotic listening of auditory stimuli is used to assess brain lateralisation by simultaneously presenting different stimuli to the left and right ears to determine which syllable was perceived as being the clearest. There is a limited, albeit dated number of studies that have examined dichotic listening performance in adults who stutter (AWS) and the results remain inconclusive. The aim of this research was to investigate whether AWS show a difference in the magnitude of the right ear advantage (REA) in both undirected and directed attentional tasks when compared with adults who do not stutter (AWNS). There were 14 right-handed participants, consisting of seven AWS and seven age and sex matched AWNS controls. All participants were screened for normal hearing. They completed a dichotic listening task, which included undirected and directed attentional listening tasks. Participants were to select the consonant-vowel (CV) pair they heard the clearest. The interaural intensity difference (IID) was modulated randomly during the undirected attention task. The results for the undirected task revealed: (1) a significant REA for AWS for the IID conditions of 0 to +21 dB and significant left ear advantages (LEA) for IIDs of -15 to -21 dB; (2) a significant REA for AWNS for the IID conditions of -9 to +21 dB and significant LEAs for IIDs of -18 to -21 dB; (3) laterality index scores with a significant IID effect but no significant group or group-by-ear interaction effects using parametric statistics. Further analysis of laterality using non-parametric statistics found significant differences between the fluency groups. In general, the findings in this study were revealing of differences between AWS and AWNS when performing dichotic listening tasks with speech stimuli. The primary difference observed between groups was in regards to the IID point at which a previous REA became a LEA. This “crossing-over” point occurred later for AWNS, indicating a strong left hemisphere advantage for the processing of speech. The earlier “crossing-over” for AWS would indicate that the right hemisphere was activated sooner for the processing of speech compared to AWNS. This activation of the right hemisphere is assumed to reflect more diffuse cerebral lateralisation for speech processing for the AWS and confirms past brain imaging studies. In the directed attention task, there was no significant difference between AWS and AWNS indicating that instances of stuttering may occur due to more automatic (bottom-up) speech processing. These findings have implications for theories of laterality and hemispheric asymmetry for phonological processing for AWS, which has been suggested to reflect a subgroup of AWS for whom cerebral dominance is related to their disfluency.

Thesis (M.Sc.)--University of Hong Kong, 2008. / Includes bibliographical references (p. 37-42).

Perception of dichotic chords (free recall and directed recall), nonsense syllables (CVs), and three-pair digits was assessed on 24 musicians and 24 nonmusicians. On the dichotic-CV and dichotic-digit free-recall tasks, there was a significant right-ear advantage, but there were no group differences. With the dichotic-chords, free-recall condition, a significant left-ear advantage was observed but no group difference. For the dichotic-chords, directed-recall conditions, the musicians performed significantly better by 10 percent than the nonmusicians. Unexpectedly, for the dichotic chords, the 62-72 percent correct performances were better on the free-recall condition than the 42-55 percent performances on the directed-recall conditions. These differences between the two response modes were attributed to the difficulty of the dichotic-chord listening tasks and the probabilities associated with the closed-set response paradigms. The findings suggest that the dichotic-chord paradigm used in this study should not be included in clinical protocols used to assess auditory perceptual abilities.

Many of the studies examining cognitive control during selective attention across different sensory modalities conflict. This study was designed to study the effect of an irrelevant visual stimulus and an auditory distraction of backward speech on a forced attention dichotic listening test. I predicted that the visual stimulus and backward speech would not have a significant effect on the ear advantage. The results showed that all subjects were able to force their attention to the ear regardless of the visual or auditory distracters. In addition, I found that an irrelevant visual stimulus affects auditory attention more so in the left visual field than the right visual field. This proves that top-down processing can override bottom-processing and auditory tasks demanding full processing capacity limit the processing of the irrelevant visual stimulus.

Thesis advisor: Lisa Feldman Barrett / A current debate ensues between the bivalent and the bipolar views of affect. This study has attempted to further support the side of bipolarity. The bipolar model of affective experience explains that affect is experienced along a single continuum and therefore a person processes only one feeling of affect at a time and cannot experience opposite states of affect simultaneously. I predicted that, in accordance with the bipolar model, participants would be unable to process semantic information from both positive and negative narratives at the same time in a dichotic listening. This inability would cause the participants to make shadowing errors when their attention shifted to the unattended channel as well as causing a vocal delay when the narratives switched auditory channels midway through the experiment. They would rate themselves in bipolar space throughout the experiment, but to then rate themselves in bivalent space when they made a summary judgment at the end of the experiment, since they are asked to combine their entire experience into a discreet rating. Twenty-one undergraduate students participated in a dichotic listening task while using the CTVG to continuously record their current state of affect in real time. The percent of errors made in shadowing, vocal delay, position on the grid for the summary judgments and the placement on the grid surrounding attention shifts were all measured. Results suggest that the structure of the affective experience follows the bipolar model. Implications of this research are discussed. / Thesis (BA) — Boston College, 2006. / Submitted to: Boston College. College of Arts and Sciences. / Discipline: Psychology. / Discipline: College Honors Program.

Thesis (M. Sc.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

For children with intractable epilepsy, surgery provides significant reduction in seizure frequency, with no significant declines in intellectual or behavioral functioning (Datta, et al., 2011). Prior to surgery, children must undergo a thorough assessment to determine the location of the seizure-focus and to evaluate risks of post-operative impairment (Lee, 2010). Currently, fMRI offers one of the most reliable and least invasive means of localizing language prior to surgery (McDonald, Saykin, William & Assaf, 2006). Dichotic listening, a behavioral task in which subjects are asked to listen to two competing stimuli simultaneously, offers a possible alternative for children who cannot complete fMRI studies. Previous studies have relied on research-based listening tasks and the type of quantitative analysis of the fMRI rarely available in the clinical setting. Instead, this study examined how well dichotic listening results predict language lateralization from fMRI within a clinical setting. Data were gathered through a records review of 13 children with intractable epilepsy referred to Austin Neuropsychology through the epilepsy treatment team at Dell Children’s Medical Center. Overall, children classified as atypical language dominance on the fMRI studies showed lower levels of right ear advantage on the dichotic listening measure. Despite this trend, a discriminant analysis using the dichotic listening results to predict fMRI classification showed no significant improvement over chance classification. A secondary analysis examined factors related to a child’s ability to complete an fMRI language study, comparing 12 children from the original sample with 6 children referred through the same process and over the same time period who could not obtain a successful fMRI determination of language lateralization. Overall, children who successfully completed the fMRI language studies showed a trend of lower levels of difficulty with behavioral regulation and higher levels of intelligence. Although the non-significant results highlight the limitations of dichotic listening as a clinical tool, the failure rate within the total sample, along with the information about the roles of intelligence and behavioral regulation, may help spur the development of alternative methods of language lateralization. / text

Thesis (M. Communication Pathology)--University of Pretoria, 2003. / Includes bibliographical references.