Behavioural and Evoked Potential Measures of Auditory Processing In Adults and Children with Unilateral Hearing Loss (UHL)

Abstract

Aims: Aims of this doctoral thesis were to 1) investigate the effects of a unilateral hearing loss (UHL) in adults and children examining several auditory abilities such as localising sound, recognising speech in noise and self-perception of hearing disability in daily life contexts due to this condition, 2) measure cortical auditory evoked potentials (CAEPs) elicited by speech sounds to explore the effects of UHL on brain responses, 3) compare group performance between normal hearing controls and the study group for behavioural and electrophysiological measures, 4) examine auditory function over time in a child with single sided deafness who received a cochlear implant and 5) monitor the pattern of change over time in an adult who had a sudden onset of single side deafness after acoustic neuroma removal and to determine the impact of his hearing device use on auditory function. Methods: Auditory skills were assessed using tests of sound localisation, spatial speech perception in noise, and self-ratings of auditory abilities (abbreviated 7-item version of Listening Inventory for Education, LIFE-7 NZ; Speech, Spatial and Qualities of Hearing questionnaire, SSQ; and Auditory Behaviour in Everyday Life, ABEL). CAEPs in noise (+5 dB signal to noise ratio) elicited by consonant-vowel naturally produced speech sounds were recorded. Performance of children and adults with UHL were compared with normal hearing participants’ results. Results: Adults and children with UHL had major, statistically significant difficulties compared to controls recognising speech in noise even when the signal was directed to the good ear, with difficulties more evident for children. Sound localisation was affected by UHL for both adults and children, however there was greater variability in children, particularly for the right ear. Adults and children reported higher levels of hearing difficulties in everyday life listening situations compared to controls. Activities which require concentration and attention were reported as the most challenging (indicating high listening effort). Brain responses showed differential changes as a function of the age. Adults with a right ear hearing loss (left ear stimulus presentation, to the better ear) showed a more symmetric hemisphere activity (N1 response) across all stimuli. CAEPs for adults with a left ear hearing loss were similar to normal hearing controls as these participants showed larger activity for electrodes located over the hemisphere contralateral to the stimulated ear (right ear presentation). Normal hearing children showed a left hemisphere dominance (P1 cortical response) regardless of the ear of stimulus presentation, and larger responses at frontal and central locations. Children with UHL did not show this dominance. Overall, for left ear UHL, P1 responses were smaller compared to right ear UHL. N250 responses were larger frontally in normal hearing children, whereas children with left ear UHL had more symmetric CAEP activity. Conclusions: People with UHL have a range of listening difficulties such as localising sound in the horizontal plane and recognising speech in noise. Children and adults and the children’s parents reported difficulties in different contexts. Questionnaire data indicated that the ability to recognise speech in different contexts and spatial hearing were perceived as most affected by a UHL for adults. Children reported difficulties in school settings mainly for noisy situations. Participants with UHL reported higher levels of need for concentration or attention during listening activities. CAEPs showed changes within the auditory cortex for children and adults. Atypical responses were observed for both groups compared to normal hearing individuals. CAEPs would be a useful tool for assessing auditory cortical function in people with UHL, providing information about the status of the neural encoding of the auditory signals to support the behavioural evidence for auditory difficulties in this population.