Objective: The frequency modulation (FM) of speech can convey linguistic information and also enhance speech-stream coherence and segmentation. The purpose of the present study was to use a clinically oriented approach to examine the effects of age and hearing loss on the ability to discriminate between stochastic patterns of low-rate FM and determine whether difficulties in speech perception experienced by older listeners relate to a deficit in this ability.
Design: Data were collected from 18 normal-hearing young adults, and 18 participants who were at least 60 years old, nine of whom had normal hearing and the remaining nine who had a mild-to-moderate sensorineural hearing loss. Using stochastic frequency modulators derived from 5-Hz low-pass noise applied to a 1-kHz carrier, discrimination thresholds were measured in terms of frequency excursion (ΔF) both in quiet and with a speech-babble masker present, stimulus duration, and signal-to-noise ratio (SNR(FM)) in the presence of a speech-babble masker. Speech-perception ability was evaluated using Quick Speech-in-Noise (QuickSIN) sentences in four-talker babble.
Results: Results showed a significant effect of age but not of hearing loss among the older listeners, for FM discrimination conditions with masking present (ΔF and SNR(FM)). The effect of age was not significant for the FM measures based on stimulus duration. ΔF and SNR(FM) were also the two conditions for which performance was significantly correlated with listener age when controlling for effect of hearing loss as measured by pure-tone average. With respect to speech-in-noise ability, results from the SNR(FM) condition were significantly correlated with QuickSIN performance.
Conclusions: Results indicate that aging is associated with reduced ability to discriminate moderate-duration patterns of low-rate stochastic FM. Furthermore, the relationship between QuickSIN performance and the SNR(FM) thresholds suggests that the difficulty experienced by older listeners with speech-in-noise processing may, in part, relate to diminished ability to process slower fine-structure modulation at low sensation levels. Results thus suggest that clinical consideration of stochastic FM discrimination measures may offer a fuller picture of auditory-processing abilities.