UBC Theses and Dissertations
Temporal jitter mimics effects of aging on word identification and word recall in noise Brown, Sasha
It is well documented that older adults, even those with normal pure-tone thresholds, tend to have more difficulty perceiving speech and comprehending language in noise compared to younger adults (e.g., CHABA , 1988). There is an increasing body of literature suggesting that as people age, changes to the auditory system occur that decrease ability to process auditory temporal information, which is crucial to the analysis of the speech signal. Recently, the hypothesis has been put forward that the ageing auditory system becomes less able to code periodicity cues or synchrony, due to a disruption to the phase-locking capabilities o f the auditory neurons (Pass, 1998; Pichora- Fuller, Schneider, Pass & Brown, 2000). It has also been proposed that degradation caused by perceptual difficulties cascades into higher-level cognitive-processing problems. From an informationprocessing perspective, like that which guides and informs the studies in this thesis, a compromised signal requires more cognitive resources to help recover the signal, thereby leaving fewer resources for other processes, such as memory, which are necessary to language comprehension. The current experiments further investigated these hypotheses by creating an . asynchrony, like that believed to occur in the aged auditory system, and applying it to the high- and low-context SPIN-R sentences, which were presented concurrently with babble at different signal-tp-noise ratios (S/N). These jittered signals were then presented to young listeners with normal hearing to determine i f the asynchrony resulted in wordidentification and word-recall performance similar to that of older adults who had participated in an earlier study (Pichora-Fuller, Schneider, & Daneman, 1995). It was found that when presented with this jittered speech, the word identification performance of young listeners hearing jittered speech almost perfectly matched the performance of older listeners when sentence context was low; however, the young failed to demonstrate the extent of benefit from high context that had been found for old listeners. Such differences in context effects were not apparent when recall was measured. It is suggested that the externally applied asynchrony resembles the asynchronous neural firings thought to characterize the auditory systems of older adults, and that memory difficulties on auditory tasks may result from an interaction between age-related perceptual and cognitive decrements.