Enhancing Speech-in-Noise Comprehension in Older Adults: An MEG Study using Rapid Invisible Frequency Tagging (RIFT)

In our everyday lives, we frequently communicate in noisy environments such as in workplaces, classrooms, public spaces, or at home. Successfully extracting meaning from speech in these situations is essential for communication and social interaction. With age, this skill often declines, making it increasingly challenging to understand speech in noisy conditions. Speech in noise perception difficulties are present even in older adults with normal audiometric thresholds (Gordon-Salant & Fitzgibbons, 1993). There are several theories explaining why this occurs, including age-related sensory deficits (Wong et al., 2010), sensitivity to distractors (Tun et al., 2002), insensitivity to pitch changes (Moore & Peters, 1992) and deficits in temporal processing (Gordon-Salant & Fitzgibbons, 1993). When the auditory speech is degraded in background noise, visual cues such as gesture and lip movements have been found to enhance attention (Fu et al., 2019) and comprehension (Park et al., 2016; Sumby & Pollack, 1954). Speech in noise comprehension has been found to improve further when using the speech amplitude envelope as visual rhythmic stimulation (Fletcher et al., 2024; Yuan et al., 2021). While studies have employed the speech amplitude envelope for tactile and neural stimulation, it remains unclear whether it can serve as a form of naturalistic visual stimulation. In this project, we focus on how speech in noise can be improved in older listeners by using a non-invasive sensory stimulation technique . In a previous MEG (Magnetoencephalography) study, we have uncovered the neural and behavioural correlates of speech in noise comprehension using rapid invisible frequency tagging (RIFT) as non-invasive sensory stimulation in younger adults (aged 18-35). RIFT involves flickering the luminance of stimuli at high frequencies above the flicker fusion threshold, making it invisible, but still evoking a steady state response in the brain (Drijvers et al., 2021; Mankowska et al., 2021; Seijdel et al., 2022; Zhigalov et al., 2019; Pan et al., 2021, 2024). Visually tagging at higher frequencies renders the flicker imperceptible , ensuring it does not interfere with the experimental task. In a dichotic audiovisual listening experiment designed to mimic a multi-speaker environment, we asked young adult participants to focus on the speech presented to one ear (task-relevant) while disregarding speech presented to the opposite ear (task-irrelevant). The auditory components of the speech were frequency tagged at 40 Hz, whereas the visual component - specifically, the speaker’s lip movements - were tagged at 55 Hz. We further manipulated the experimental conditions by modulating the amplitude of the visual RIFT signal according to the speech envelope, corresponding either to the task-relevant or task-irrelevant audio stream. Results showed that amplitude modulation of the visual RIFT by the task-relevant speech envelope enhanced speech comprehension as well as coherence between RIFT and MEG signals. In the present project, we will investigate whether this approach can enhance speech-in-noise comprehension in older adults . We aim to compare the neural and behavioural responses between younger adults (data already collected) to that of older adults (aged 65-80) (data collection pre-registered here).