Heart rate variability (HRV) is the amount to which the period between individual heartbeats varies. This measurement can be used as a proxy to measure bodily stress. A higher HRV corresponds to more parasympathetic nervous activity and lower bodily stress, while a lower HRV corresponds to more sympathetic nervous activity and therefore higher bodily stress. The goal of this experiment was to examine changes in HRV when humans are exposed to different frequencies of noise (white, pink, and brown, with ambient noise and silence used as controls). By observing people’s HRV in response to various frequencies of noise, it was found that HRV increases in relation to noise frequency. Although the individual HRVs changed for each participant, likely because of the differences in their audio processing systems and baseline bodily stress, higher-frequency noise was associated with a higher HRV for all of them, confirming the directly proportional relationship that was hypothesized. This relationship is likely a result of evolutionary adaptations among early humans, in which higher-frequency environmental noise signaled the presence of plentiful resources and a calm environment, while lower-frequency environmental noise signaled threat, i.e., the presence of predators or inclement weather. The connection between HRV and noise frequency may be relevant in further studies with a broader range of individual frequencies of stochastic noise.

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