Noise, stress, and the perception of loudness: exploring the mechanistic bases of tinnitus and hyperacusis with the use of technological advances

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Tinnitus is associated in most cases with a natural decline in hearing function over a lifetime. Recent data show that its prevalence is on the rise among younger age groups. Hyperacusis, an increased sensitivity to external sounds, possibly shares with tinnitus common mechanisms including upregulated central gain function. Remarkably, both appear to be exacerbated by the individual's stress status. However, little is known regarding noise and stress interactions in normal hearing adults. We therefore propose to investigate dynamic responses to noise and stress, characterizing i) autonomic cardiac responses to noise-related, physical and psychological stress (Part 1), and ii) addressing the sensory and affective dimensions of loudness in relation to differential facial expression patterns with which they are putatively associated (Part 2). In Part 1, we propose to transform the Auditory Research Platform (ARP)'s use from a hearing protection device into a powerful research instrument taking advantage of the internal microphone located in the occluded auditory canal to extract rhythmic cardiac signals for assessment of autonomic responses to noise and stress and test hypotheses concerning differences between male and female as well as young and aging adults. Heart beat detection from ARP acoustic recordings will be used to derive times series of intervals between normal beats (NN) from normal-hearing adults exposed to several experimental conditions (~5 min duration). The data will then be subjected to heart rate variability (HRV) analysis to determine power for the high (HF, 0.15-0.4 Hz) and low frequency (LF, 0.04-0.15 Hz) spectral components as measures of parasympathetic responses and changes in sympathetic/ parasympathetic balance, running ANCOVAs (Sex and Age as between- and Conditions as within- subjects variables, and questionnaire scores as co-variates) on HR and HRV indices. In Part 2, we will investigate the hypothesis that normal hearing adults, when exposed to sounds varying in their sensory (intensity) and affective dimensions (aversive versus neutral or pleasant), display specific patterns of facial expressions. We will therefore record dynamic facial expressions of participants when. Rather than using the classical manual and time-consuming Facial Action Coding System (FACS), we propose to make use of a machine-learning approach which can rapidly handle large bodies of complex data with heterogeneous distributions while also - in contrast to classical FACS - allowing the identification of novel patterns to predict specific classifiers, here sensory and affective loudness ratings, as the most relevant indices for each of these dimensions. These studies address dynamic physiological responses to noise and stress, both on the rise in our contemporary environment, using novel approaches that hold the promise of providing - in a real-life ambulatory context - insights into the mechanistic bases of hearing disturbances.