People with clinically normal hearing thresholds may still encounter challenges understanding speech in adverse conditions, yet identifying such suprathreshold deficits has proven challenging. Motivated by auditory-modeling studies proposing an analysis of across-frequency coherence in the backend of speech-intelligibility (SI) prediction frameworks, we explored a ‘distortion-sensitivity’ approach to characterize listeners’ perception of across-frequency phase coherence as a potential suprathreshold factor influencing speech perception. While a loss of phase coherence across frequency bands, such as through phase jittering, has been shown to be detrimental for SI in young normal-hearing listeners, less is understood about the sensitivity of older individuals and those with listening challenges to such distortions.

We manipulated across-frequency coherence by independently adding a random phase component to each frequency channel of a speech-and-noise mixture presented at a signal-to-noise ratio of 5 dB. SI was measured based on the spread of the distribution of phase values. Additionally, we obtained the just-noticeable-differences (JNDs) for across-frequency phase jitter, as well as speech reception thresholds (SRTs) for undistorted speech in the presence of stationary, fluctuating and speech-like maskers. Data from 10 young and 10 older NH listeners revealed lower JNDs in the older listener cohort, suggesting a reduced sensitivity to across-frequency coherence. However, no changes in the perception of jittered speech was observed. The results from this experimental work will be translated into model parameters, enabling the evaluation of a suprathreshold distortion component within a computational framework for the predicting the measured SRTs.