EEG-based assessment of listening effort in deaf and normal hearing persons
Listening effort represents a hot topic in auditory cognitive neuroscience , and it is well-known that a typical paradigm able to elicit such particular cognitive effort is represented by speech in noise tasks. Furthermore, in the last years it has been ever more felt the need for the identification of an “objective measure of listening effort” , aimed at identifying more sensitive assessments of the way an auditory task is undertaken by a listener, especially in case of hearing impairments. Among these measures based on neurophysiological measures we can coarsely divide between measures based on central nervous system activity and autonomic nervous system activity, and EEG-based indices belongs to the former ones. In the area of research I am presenting it was employed the paradigm of speech in noise task in association with the study of EEG rhythms, essentially parietal alpha   and frontal theta   as indices of listening effort.
It is interesting to investigate listening effort both in children and adults, given the frequent difference in the etiology of deafness in these two populations, more often related to congenital reasons in the first group and to a later acquisition in the second group. Concerning children with asymmetric hearing loss, we found significantly higher parietal alpha power levels in the “binaural noise” and in the “noise to the worse hearing ear” conditions (that were difficult but still feasible conditions) than in the “quiet” (too easy) and “noise to the better hearing ear” (too difficult) conditions (p < 0.001) . Conducting the same paradigm on adult unilateral cochlear implant users, we similarly found during the noise to the worse hearing ear condition, in the pre-stimulus phase, higher levels of parietal alpha power, in accordance to a preparatory role for alpha  for attended stimuli. Furthermore, we found higher levels of frontal theta power during the listening phase of the same condition, that also reported the higher percentage of correct responses, supporting a more sustained effort but also higher processing and efficiency for it . Concerning children, we also investigated single side deaf patients, in comparison to normal hearing children, undergoing as well a speech in noise task. Results suggested for both theta and alpha rhythms that normal hearing children by default lateralized in the left hemisphere in the Broca’s area, while single side deaf children lateralized on the base of the background noise direction .
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