Background: Previous research has suggested that children exposed to more early-life stress show worse mental health outcomes and impaired cognitive performance in later life, but the mechanisms subserving these relationships remain poorly understood. Method: Using miniaturised microphones and physiological arousal monitors (electrocardiography, heart rate variability and actigraphy), we examined for the first time infants' autonomic reactions to environmental stressors (noise) in the home environment, in a sample of 82 12-month-old infants from mixed demographic backgrounds. The same infants also attended a laboratory testing battery where attention-and emotion-eliciting stimuli were presented. We examined how children's environmental noise exposure levels at home related to their autonomic reactivity and to their behavioural performance in the laboratory. Results: Individual differences in total noise exposure were independent of other socioeconomic and parenting variables. Children exposed to higher and more rapidly fluctuating environmental noise showed more unstable autonomic arousal patterns overall in home settings. In the laboratory testing battery, this group showed more labile and short-lived autonomic changes in response to novel attention-eliciting stimuli, along with reduced visual sustained attention. They also showed increased arousal lability in response to an emotional stressor. Conclusions: Our results offer new insights into the mechanisms by which environmental noise exposure may confer increased risk of adverse mental health and impaired cognitive performance during later life.

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The differential sensitivity hypothesis argues that environmental sensitivity has the bivalent effect of predisposing individuals to both the risk-inducing and development-enhancing influences of early social environments. However, the hypothesis requires that this variation in environmental sensitivity be general across domains. In this study, we focused on neural sensitivity and autonomic arousal to test domain generality. Neural sensitivity can be assessed by correlating measures of perceptual sensitivity, as indexed by event-related potentials (ERP) in electrophysiology. The sensitivity of autonomic arousal can be tested via heart rate changes. Domain generality was tested by comparing associations in perceptual sensitivity across auditory and visual domains, and associations between sensitivity in sensory domains and heart rate We contrasted ERP components in auditory (P3) and visual (P1, N290 and P4) detection-of-difference tasks for N=68 infants longitudinally at 6 and 12 months of age. Domain generality should produce correlated individual differences in sensitivity across the two modalities, with higher levels of autonomic arousal associating with increased perceptual sensitivity. Having controlled for multiple comparisons, at 6 months of age, the difference in amplitude of the P3 component evoked in response to standard and deviant tones correlated with the difference in amplitude of the P1 N290 and P4 face-sensitive components evoked in response to fearful and neutral faces. However, this correlation was not found at 12 months of age. Similarly, autonomic arousal negatively correlated with neural sensitivity at 6 months but not at 12 months. The results suggest neural perceptual sensitivity is domain-general across auditory and visual domains, and is related to autonomic arousal at 6 months but not at 12 months of age. We interpret these findings within a neuroconstructivist framework and with respect to the concept of interactive specialisation. By 12 months of age, more experience of visual processing may have led to top-down endogenous attention mechanisms that process visual information in a way that no longer associates with auditory perceptual sensitivity.

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