The time course of steam segregation in nonnative listeners

Younger nonnative speakers with good hearing find it more difficult to comprehend speech than do younger native speakers of the language, especially in noisy situations. Older native speakers of the language also appear to find it difficult to understand speech in their native language in noisy environments, although it is quite likely that the reasons for these difficulties differ from those responsible for the problems younger nonnative listeners experience. In a previous study (Ben-David, Tse & Schneider, 2012), even though Speech Recognition Thresholds (SRTs) were, on average, higher (worse) for older adults than for younger adults, both groups benefited from a delay between the onset of a noise masker and the presentation of the speech target, with SRTs improving as the onset delay increased. However, when the masker was a babble of voices only the younger listeners benefitted from an onset delay between the babble and the speech target. In the current study, we used the same task with two groups of 30 younger nonnative English speakers: recent arrivals to Canada, and long-term residents of Canada. The results showed that the speech recognition thresholds for all younger listeners improved at the same rate regardless of their linguistic status as a function of the delay between the onset of the target speech and the onset of both noise and babble maskers. When the masker was babble, speech recognition thresholds were, on average, lower (better) for both groups of younger nonnative speakers than for older native speakers. But, with a noise masker, the function relating thresholds to onset delay was higher (worse) for recent arrivals (younger adults who arrived in Canada after the age of 15) than for older native speakers. The relevance of these findings to age-related changes in auditory scene analysis will be discussed.