Split listening: A cognitive investigation of speech perception in adverse conditions

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"Cognitive Listening" refers to the study of how memory and attention processes contribute to speech perception in challenging conditions (e.g., noise, distraction). The claim that good cognitive abilities underpin successful listening is broadly confirmed for older and/or hearing-impaired listeners. In those groups, high working memory (WM) capacity is associated with better performance in speech-in-noise tasks. For young adults with normal hearing, however, the link between cognition and listening proficiency is unclear. There are four reasons for this: (1) Young, normal-hearing adults might not generate sufficient individual variability on cognitive measures to detect reliable associations with listening performance. A majority of experiments are, thus, under-powered. Cognitive listening studies therefore need to be run with larger samples.(2) Most studies have focused on adverse conditions involving energetic masking (EM), that is, conditions in which the signal is degraded (e.g., background noise). Evidence suggests that cognition is of little help for tasks that are intrinsically "data-limited". Cognitive listening should therefore also be investigated when challenges arise from a non-EM source.(3) Semantic context can mitigate the effects of adverse listening conditions, hence making cognitive support redundant or difficult to detect. Semantic context should therefore be taken into account when modelling cognitive listening.(4) Listening performance (e.g., number of words in a sentence that are correctly recognised) may not be the most sensitive measure of how cognitive functions support listening because a given performance level can hide meaningful differences in individual cognitive effort. A measure of mental effort should therefore be included when modelling cognitive listening. The aim of this project is to systematically address the above challenges and provide a comprehensive understanding of the interaction between hearing and cognitive processes in adults with normal hearing. The project will include large-scale online experiments and targeted in-lab experiments. The online experiments will be powered to detect any modulating effects of individual WM differences on listening performance and will establish the conditions under which WM contributes to speech understanding and perceived effort. These conditions will then be inspected more closely in the lab using a physiological measure of listening effort, the task-evoked pupil response, a recognised marker of effort 'in the moment' (i.e., during listening). Both online and in-lab experiments will use our newly developed "split-listening" paradigm. In this paradigm, participants have to track two simultaneous voices. The relative spatial location of the two voices is manipulated in four incremental steps, from collocated, i.e., straight ahead of the listener (diotic), to fully lateralised (dichotic). The spatial manipulation provides a powerful way of pitting EM against attention-driven (i.e., cognitive) demands, with high EM and low attention demands in diotic listening vs low EM and high attention demands in dichotic listening. Pilot data from our lab have confirmed the ability of this paradigm to quantify the competing dynamics between energetic and cognitive processes. The pilot data have also shown that this paradigm is amenable to online testing on a large scale. Its parametric manipulation of EM and attention demands makes it an ideal candidate for pupillometric assessment. As a whole, the project offers a programmatic approach to the cognitive and physiological building blocks of effortful listening. The data on individual differences gathered in the online experiments will be valuable in elucidating the cognitive contributors to healthy hearing beyond the traditional hearing test and, in doing so, pave the way for targeted interventions in clinical populations (e.g., individuals with a hearing loss and/or dementia).