Medical Bionics - Theses
Permanent URI for this collection
Search Results
1 - 2 of 2
-
ItemBehavioural and objective measurements of listening effort( 2021)Listening effort has been defined as the mental effort exerted to understand auditory stimuli (Pichora-Fuller et al, 2016a). In many cases it is one of the causes of isolation and poor quality of life for people with hearing aids and cochlear implants. One way to mitigate this problem is to assess listening effort during the fitting of hearing devices and then use these measurements to optimise device settings to improve audibility while at the same time minimising listening effort. However, at the moment, clinical practice lacks a standardised protocol for the assessment of listening effort. In this project, a behavioural test for the assessment of task difficulty was developed and validated. As was the feasibility of using fNIRS for the assessment of listening effort. The first study in this thesis focused on the development and validation of a behavioural dual task test for assessment of task difficulty. The test consisted of identification of the last word of each sentence in lists of seven sentences each, and recall of those last words after the presentation of each list. The test was implemented with Australian speech material, to minimise possible confounding factors due to accent and dialect dissonances when applied to the Australian population. The test was applied to twenty-four normal hearing participants. The results showed that, both identification and recall scores could predict differences in difficulty between speech presented in noise and speech presented in noise in which a binary mask noise reduction algorithm was applied to the speech mixture. The implemented test could be used in the Australian research practice to compare different hearing devices and processing algorithms at high levels of speech intelligibility. The second study investigated the feasibility of using fNIRS for assessment of listening effort. More specifically, in this study fNIRS was used for identifying cortical neuronal biomarkers of listening effort in the left inferior frontal gyrus (LIFG) and bilateral posterior superior temporal gyrus (pSTG). The findings of the study suggest the existence of task related concentration changes of oxy- and deoxy- haemoglobin during the expected exertion of listening effort. Furthermore, when listening effort was modulated by manipulation of motivation and task demands, the change in concentration of oxyhaemoglobin, followed the behaviour expected for listening effort. However, the results of this study were not statistically significant due to the high level of uncontrolled variability on the data. These results suggest a potential for fNIRS in the assessment of listening effort, however, more investigation needs to be done to optimise the protocols for assessment of listening effort and improve effect size. The third study continued with the investigation of the feasibility of using fNIRS for the assessment of listening effort. However, in this study, rather than using fNIRS for monitoring cortical neuronal activity, it was used for monitoring concentration changes of total haemoglobin in the extracerebral compartment (scalp and skull), associated with the activation of the autonomic nervous system. The findings of this study suggested the existence of task related concentration changes of total haemoglobin in the extracerebral compartment. When compared with the expected behaviour of listening effort modulated by manipulation of motivation and task demands, it was found that the concentration changes of total haemoglobin in the extracerebral compartment followed the expected trend of behaviour of listening effort, but again, these results were not statistically significant. The results suggests that fNIRS could potentially be used for assessment of listening effort, not just due to the capability of monitoring cortical neuronal activity, but also due to the capability of monitor activation in the autonomic nervous system. In this project, behavioural and objective measurements of listening effort were investigated. The work reported in this thesis has shown that behavioural methods can be used for assessment of listening task difficulty. But also, the experiments reported in this thesis investigated the feasibility of fNIRS for the assessment of listening effort. It was determined that fNIRS has the potential for assessment of listening effort because it facilitates the study of its different aspects, associated with cortical neural activity, but also, with activation of the autonomic nervous system when listening under challenging conditions. This work provides a base for future research that should be focused in determining a protocol for measurement of listening effort that integrates cortical neuronal and systemic components extracted from the fNIRS signal to better understand listening effort.
-
ItemLanguage processing in cochlear implant users using fNIRS( 2018)Cochlear implant (CI) users differ in their auditory speech understanding ability. This variability is partly due to variability in deafness history and pathology, and partly due to functional brain changes that are likely to occur during deafness and after implantation. By measuring cortical activity in CI users, a relation between functional changes in language associated regions of their brain and speech understanding may be revealed. However, when investigating cortical activity in CI users, commonly-used neuroimaging techniques have limitations. For example, EEG and fMRI may suffer from magnetic or electrical artefacts, and PET imaging is invasive for participants. The studies described in this thesis used a non-invasive technique – functional near-infrared spectroscopy (fNIRS) – to investigate cortical activity in CI users related to speech understanding and the integration of audio-visual speech cues. Compared to fMRI, fNIRS also has the advantages of being quiet (not suffering from the loud magnetic scanning noise) thus suitable for auditory-related tasks, and more tolerant of body movement. The first study determined whether fNIRS measures of cortical activity in post-lingually deafened CI users when listening to or watching speech are correlated with their auditory speech understanding. The fNIRS results showed that speech-evoked cortical activity in CI users that was not only different from normal-hearing listeners but also was negatively correlated with the speech understanding ability. That is, CI users who had poorer auditory speech understanding ability showed higher fNIRS activation in certain brain regions of interest when listening to or watching speech. The increased brain responses might be related to brain functional changes that occurred in CI users during deafness and after implantation for visual speech processing or more listening effort and more neural responses that were used by CI users to process auditory speech. The second study determined whether audio-visual (AV) integration of speech cues in post-lingually deafened CI users is different from that in their similar-aged normal-hearing adults. Participants’ reaction times, response accuracy, and cortical activity were measured when performing different speech identification tasks. A novel method was proposed that combined a probability model and a cue integration model to quantify the amount of AV integration based on response accuracy measures. Consistently, behavioural results using response accuracy and reaction time measures did not show better AV integration in CI users compared to people who had normal hearing. In addition, fNIRS measures of cortical activity did not show AV integration in either CI users or normal-hearing adults. The third study determined whether aging affects AV integration in people who have normal hearing when responding to speech using the same behavioural and fNIRS measures as in the second study. Again, fNIRS results did not show AV integration in either younger or older participants. Behavioural results found no significant difference in AV integration between the older and young participants using both reaction time and response accuracy measures. This thesis integrates knowledge from multisensory neuroscience and psychophysics and uses a novel brain imaging technique to measure cortical activity in CI users for language processing. Results in this thesis showed that this novel imaging technique – fNIRS – could be implemented to examine the variances in auditory speech understanding among CI users. It makes a new advance in the way that multisensory abilities are measured behaviourally, by combining models of optimal and minimum integration. Results in this thesis found that there was no significant difference between CI users and normal-hearing adults in the integration of audio-visual speech cues. Neither was there a significant effect of aging on AV integration.