Age-related changes in the auditory system have been attributed to three separate factors:​ outer hair cell damage, changes in endocochlear potentials, and loss of neural synchrony (Mills et al., 2006). While loss of neural synchrony may have little effect on audiometric thresholds, it is thought to contribute to difficulties understanding speech in noise.

An intensity discrimination experiment was performed in quiet, broadband, and notched noise. While two of the older adults exhibited intensity discrimination thresholds equivalent to those of the younger adults, the majority of the older adults had much larger thresholds than younger adults the noise conditions. Importantly, these older adults did not exhibit smaller thresholds in broadband noise compared to notched noise as was the case for younger adults. Since temporal fine structure cues are present in the broadband--but not the notched-noise condition, this pattern of findings suggests that these older adults were not as able as younger adults were in making use of temporal fine structure cues.

A jitter algorithm was used to simulate a loss of synchrony and a smearing algorithm was used as a control for the unintended spectral distortion produced by the jitter algorithm. Over the course of five experiments, young and old adults with good audiograms in the speech range were presented with sentences under a variety of processing conditions using a range of parameters to examine the effect of a loss of synchrony on speech perception in noise.

In general, the jitter condition resulted in a significant decline in word identification compared to both the smear and intact conditions for both age groups. This suggests that a loss of synchrony can have a deleterious affect on speech intelligibility in noise. Furthermore, the performance of the young adults in the jitter conditions were similar to that of the older adults in the intact conditions for low-context sentences. Thus, the jitter condition appears to simulate this neural aspect of auditory aging in otherwise healthy young ears.