Abstract
Older listeners are more likely than younger listeners to have difficulties in making temporal discriminations among auditory stimuli presented to one or both ears. In addition, the performance of older listeners is often observed to be more variable than that of younger listeners. The aim of this work was to relate age and hearing loss to temporal processing ability in a group of younger and older listeners with a range of hearing thresholds. Seventy-eight listeners were tested on a set of three temporal discrimination tasks (monaural gap discrimination, bilateral gap discrimination, and binaural discrimination of interaural differences in time). To examine the role of temporal fine structure in these tasks, four types of brief stimuli were used: tone bursts, broad-frequency chirps with rising or falling frequency contours, and random-phase noise bursts. Between-subject group analyses conducted separately for each task revealed substantial increases in temporal thresholds for the older listeners across all three tasks, regardless of stimulus type, as well as significant correlations among the performance of individual listeners across most combinations of tasks and stimuli. Differences in performance were associated with the stimuli in the monaural and binaural tasks, but not the bilateral task. Temporal fine structure differences among the stimuli had the greatest impact on monaural thresholds. Threshold estimate values across all tasks and stimuli did not show any greater variability for the older listeners as compared to the younger listeners. A linear mixed model applied to the data suggested that age and hearing loss are independent factors responsible for temporal processing ability, thus supporting the increasingly accepted hypothesis that temporal processing can be impaired for older compared to younger listeners with similar hearing and/or amounts of hearing loss.
Highlights
It has been shown that older listeners often do more poorly at detecting or discriminating temporal differences imposed on stimuli at the various time scales relevant to speech understanding (e.g., Ross et al, 2007; Fitzgibbons and Gordon-Salant, 2010; Ruggles et al, 2011; Moore et al, 2012)
Results of a repeated-measures ANOVA performed on thresholds averaged between ears with stimulus as a withinsubjects factor and age group as a between-subject factor is shown in Table 4, where it can be seen that age group was a significant factor and accounted for 31% of the variance, while stimulus type was significant and accounted for 14% of the
Unlike the monaural gap discrimination thresholds, there were no reliable differences among the three chirp stimuli, while thresholds were substantially lower for all three chirp stimuli relative to the tone burst
Summary
It has been shown that older listeners often do more poorly at detecting or discriminating temporal differences imposed on stimuli at the various time scales relevant to speech understanding (e.g., Ross et al, 2007; Fitzgibbons and Gordon-Salant, 2010; Ruggles et al, 2011; Moore et al, 2012). There are a large number of studies that have looked at performance differences between older and younger listeners at longer time scales sometimes associated with “envelope” processing (see, for example, Gordon-Salant and Fitzgibbons, 1999; Roberts and Lister, 2004; Lister and Roberts, 2005; Ajith and Sangamanatha, 2011). One persistent difficulty in studies of the impacts of aging on both TFS and envelope processing is the confounding of age and hearing loss due to the prevalence of age-related hearing loss in the samples tested, especially given the extensive evidence that cochlear damage reduces sensitivity to temporal information (e.g., Buss et al, 2004; Lorenzi et al, 2006; Henry and Heinz, 2012; reviewed in Moore, 2014). The common occurrence of age-related hearing loss complicates the interpretation of the impacts of age on temporal processing for the majority of published studies, especially if one considers the possibility that even relatively small changes in hearing could have substantial impacts on temporal processing ability (e.g., Takahashi and Bacon, 1992; He et al, 2008; Ruggles et al, 2011).
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