Value of a Kurtosis Metric in the Evaluation of Noise-Induced Hearing Loss

The fundamental problem with current noise exposure criteria (e.g., ISO 1999) is their reliance on an energy metric to quantify an exposure, which completely ignores the effects of temporal characteristics of noise exposure known to be important in affecting noise-induced hearing loss (NIHL). Noise usually has a rather complex temporal structure, which can be expressed as a combination of continuous steady-state noise and various transient impulsive noises. A large number of animal experiments and epidemiological studies have shown that complex noise presents a greater hearing loss risk than continuous noise. Therefore, a metric is needed to account for this increased risk when analyzing hearing loss caused by complex noise. Over the last 20 years, multi-national collaborative teams have addressed the issue of complex noise exposure. Both animal and human research studies have found that the kurtosis statistic, a metric that describes the probability for a noise signal to include high-level impulsive events, can account for the risks observed for groups with complex exposures. Kurtosis holds great promise in addressing the complexity associated with measuring and characterizing such exposures. Many issues focused on kurtosis can be applied not only to terrestrial mammals but also to marine mammals. A better understanding of the role of the kurtosis metric in NIHL may lead to its incorporation into a new generation of more predictive hearing risk assessments for noise exposure.