This study examined younger (n = 16) and older (n = 16) listeners' processing of dysarthric speech-a naturally occurring form of signal degradation. It aimed to determine how age, hearing acuity, memory, and vocabulary knowledge interacted in speech recognition and lexical segmentation. Listener transcripts were coded for accuracy and pattern of lexical boundary errors. For younger listeners, transcription accuracy was predicted by receptive vocabulary. For older listeners, this same effect existed but was moderated by pure-tone hearing thresholds. While both groups employed syllabic stress cues to inform lexical segmentation, older listeners were less reliant on this perceptual strategy. The results were interpreted to suggest that individuals with larger receptive vocabularies, with their presumed greater language familiarity, were better able to leverage cue redundancies within the speech signal to form lexical hypothesis-leading to an improved ability to comprehend dysarthric speech. This advantage was minimized as hearing thresholds increased. While the differing levels of reliance on stress cues across the listener groups could not be attributed to specific individual differences, it was hypothesized that some combination of larger vocabularies and reduced hearing thresholds in the older participant group led to them prioritize lexical cues as a segmentation frame.
Increased loudness and reduced rate exhibited differential effects on listeners' perceptual processing of dysarthric speech. The current study highlights the insights that may be gained from a cognitive-perceptual approach.
A growing number of studies have attempted to address the cognitive–linguistic source of intelligibility deficits in dysarthria. These have focused predominantly on the ability of young adults with normal hearing to decipher dysarthric speech. However, dysarthria is commonly associated with aging; older listeners often form primary communication partners. It is also known that older adults exhibit difficulty understanding speech that has been temporally or spectrally degraded. It follows that the spectral and temporal degradations present in dysarthric speech may pose a greater perceptual challenge for older, as opposed to younger, listeners. Twenty younger listeners (mean age = 20 yr) and 15 older listeners with good hearing for their age (mean age = 65 yr) transcribed the speech of individuals with moderate hypokinetic dysarthria. Percent words correct (intelligibility) was calculated and underlying error patterns at the suprasegmental and segmental levels of processing were examined. While the younger and older listener groups achieved similar intelligibility scores, the younger group showed greater reliance on syllabic strength cues to inform word boundary decisions. Similar levels of attention to segmental cues were observed across both groups. These results suggest that the recognition of dysarthric speech may be comparable across younger and older listeners.
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