The overarching goal of the proposed research is to identify the underlying causes of speech understanding problems in older adults. Older listeners, with or without significant hearing loss, often have much greater difficulty understanding speech in the presence of competing sounds than do younger listeners (CHABA, 1988;Dubno et al., 1984;Duquesnoy, 1983). For hearing-impaired listeners, differences in degree of hearing loss (or audibility) account for a large portion of the variance in listeners'ability to understand speech in the presence of competing sounds, but other factors (e.g., cognitive or central auditory factors) play an important role for both hearing-impaired and normal-hearing listeners (see Houtgast &Festin, 2008;Akeroyd, 2008;Humes, 2007;Humes &Dubno, 2010;Humes, Kidd, &Lentz, 2013). One promising hypothesis, which has received relatively little attention to date, is that effective speech understanding in the presence of competing sounds depends strongly on the ability to follow the temporal structure of an utterance and to accurately anticipate the timing of speech events through a process of attentional entrainment. According to the entrainment hypothesis (see Large &Jones, 1999;McAuley et al., 2006) the ability to attentionally track the temporal patterns of speech helps listeners to perceptually isolate and resolve the details of a single talker's speech by enhancing attention to speech events that correspond to a talker's temporal pattern. Moreover, accurate extrapolation of temporal patterns through inaudible or partially audible portions of an utterance is proposed to facilitate the integration of intermittent "glimpses" of speech by incorporating them in a common temporal framework. This general hypothesis will be investigated through a series of experiments that test the predictions of entrainment theory in a speech context, in combination with a new test battery that assesses individual differences in entrainment ability. A sample of 1000 young and older listeners with and without hearing loss will be tested, using shaped amplification to ensure audibility for hearing- impaired listeners. The project will employ a combination of behavioral and neurophysiological measures to determine how entrainment ability is related to speech understanding, while controlling for individual differences in basic auditory capabilities and cognitive abilities previously shown to be important for speech perception.
The present proposal will investigate the role of individual differences in attentional entrainment and neural synchrony in speech understanding under difficult listening conditions, for both young and older listeners. By identifying the roles of thee factors, along with a variety of auditory and cognitive abilities, the research will be useful in predicting hearing-aid success, in developing training methods for improving the perception of speech in noise, and in the development of hearing-aid signal-processing strategies that facilitate attentional entrainment by enhancing relevant temporal patterns.