Auditory and cognitive skills in adults with reported listening in noise difficulties

Some adults with and without hearing loss struggle to understand speech in adverse listening situations. In a US and UK based prevalence study, speech understanding in noise difficulty in adults with clinically normal audiograms was reported to be 2.9% and 4% respectively. Similarly, there are a several survey studies that have shown dissatisfaction with hearing aids particularly in the presence of noise. What causes adults with and without hearing loss to experience listening difficulties in noise? The motivation of the current research comes from the auditory-cognitive interactions framework and its subsequent model Framework for Understanding Effortful Listening (FUEL). The models have proposed that both auditory and cognitive skills are pre-requisites for understanding speech particularly in the presence of noise. The objective of the first study (study 1) was to investigate the auditory and cognitive skills in adults with clinically normal hearing sensitivity and reported listening in noise difficulties. The second objective was to assess the auditory and cognitive skills in individuals with bilateral mild-moderate to moderately severe sensorineural hearing loss with reported speech understanding in noise difficulty (study 2). The Speech Spatial and Qualities Hearing Scale 12 (SSQ12) was used to evaluate the listening difficulties in 12 different listening scenarios. Study 1 included twenty adults with normal hearing and reported listening in noise difficulties and study 2 included 10 adults with hearing loss. In addition, there was a control group of twenty-two adults with normal hearing with no reported listening in noise concerns. Both studies assessed auditory skills using behavioural and electrophysiological measures (Cortical evoked potentials; CAEPs). Behavioural measures of auditory processing and cognitive measures showed no differences between adults with and without listening difficulties in noise, irrespective of hearing loss. Electrophysiological responses, however, showed distinct differences in both studies. Study 1 investigated N400 to semantically congruent-incongruent sentences and adults with listening difficulties showed small or absent N400 in quiet compared to the control group based on area under the curve. Cluster permutation analysis conducted within the groups across congruent-incongruent sentences using dependent samples t-test confirmed the presence of clusters in the centro-frontal electrodes only for the control group. Presence of N400 response indicates one’s ability to accurately predict key words based on the context. There was no difference for the onset responses (P1-N1-P2) to the sentences across the two groups, indicating similar percept across the two groups to the start of the sentence. In-addition, time frequency analysis carried out showed stronger synchronised alpha oscillations in the control group when compared to the group having individuals with listening in noise concerns. These strong alpha oscillations for the control group may indicate that the control group have a better ability to maintain their attention throughout the task. In study 2 the group with hearing loss showed similar results to study 1, there were differences in the time-frequency analysis of the electrophysiological data (/da/ in quiet and 8dB SNR). Within group analysis showed significant synchronised alpha oscillations only in the control group, indicating that the control group provided more attention and displayed more inhibition during the passive listening task. The current research cannot fully explain the listening difficulties. For instance, one of the aspects that we have not considered is assessment of listening difficulties in realistic situations. One factor recommended in the FUEL model is motivation, which we have not explored in the current research. Listening effort is another aspect that has not been considered in the current research on why some adults struggle to understand speech in everyday listening situations. Nevertheless, the current project has provided some insight. The significant differences on the electrophysiological measures that implicate cognitive skills, are promising.