Comparing lexically guided perceptual learning in younger and older listeners

Abstract

Numerous studies have shown that younger adults engage in lexically guided perceptual learning in speech perception. Here, we investigated whether older listeners are also able to retune their phonetic category boundaries. More specifically, in this research we tried to answer two questions. First, do older adults show perceptual-learning effects of similar size to those of younger adults? Second, do differences in lexical behavior predict the strength of the perceptual-learning effect? An age group comparison revealed that older listeners do engage in lexically guided perceptual learning, but there were two agerelated differences: Younger listeners had a stronger learning effect right after exposure than did older listeners, but the effect was more stable for older than for younger listeners. Moreover, a clear link was shown to exist between individuals' lexical-decision performance during exposure and the magnitude of their perceptual-learning effects. A subsequent analysis on the results of the older participants revealed that, even within the older participant group, with increasing age the perceptual retuning effect became smaller but also more stable, mirroring the age group comparison results. These results could not be explained by differences in hearing loss. The age effect may be accounted for by decreased flexibility in the adjustment of phoneme categories or by age-related changes in the dynamics of spokenword recognition, with older adults being more affected by competition from similar-sounding lexical competitors, resulting in less lexical guidance for perceptual retuning.In conclusion, our results clearly show that the speech perception system remains flexible over the life span.Keywords Perceptual learning . Speech perception . Aging . Individual differencesNumerous studies have shown that "ideal" listeners-that is, young, normal-hearing, highly educated listeners-can adapt to idiosyncratic pronunciations through lexically guided perceptual learning in speech perception (McQueen, Cutler, & Norris, 2006;Norris, McQueen, & Cutler, 2003; for an overview, see Samuel & Kraljic, 2009), and are thus able to tune in to a speaker to understand him or her better. The lexically guided perceptual learning effect has been shown using a variety of exposure and test paradigms-for instance, lexical decision and phonetic categorization (e.g., Norris et al., 2003), short story presentation and phonetic categorization (e.g., Eisner & McQueen, 2006), and a picture verification procedure (e.g., McQueen, Tyler, & Cutler, 2012). In the exposure phase, listeners are exposed to an idiosyncratic sound-for instance, a sound ambiguous between [s] and [f] (/ f / s /), which would be learned as /s/ if it was heard in words such as platypus (because platypus is an existing word in English, whereas platypuf is not), but as /f/ in words such as giraffe (which is an existing word in English, whereas giras is not). This perceptual-learning effect is caused by a temporary change in phonetic category representations, rat...

The Role of Lexical Status and Individual Differences for Perceptual Learning in Younger and Older Adults

“…The direction of this attention-switching effect remains consistent with previous work (McAuliffe & Babel, 2016;Scharenborg et al, 2015), suggesting that attending to the signal in a lexically-guided learning task is detrimental to learning compared to maintaining attention at the task-level. We also found differing results from Scharenborg and Janse (2013) in terms of the effect of accepting ambiguous target words on learning-consistent behaviour.…”

“…One block was presented during the pretest and three blocks were presented during the posttest (90 trials). The posttest was presented as three consecutive blocks immediately following the exposure phase because previous perceptual learning work comparing older and younger adults found different patterns of learning between the two age groups as the posttest progressed (Scharenborg & Janse, 2013).…”

“…Six participants (Mage=21.0) piloted the test continuum in a 2AFC task to ensure the category boundary fell in the middle of the continuum. After piloting and based on previous work (Scharenborg & Janse, 2013;Scharenborg et al, 2015), steps 4, 6, 7, 8, and 10 were chosen from the original 11-step continuum for use in the pre-and post-tests.…”

“…The random effect slope from the alternate learning task was then used as a predictor of learning consistency in these models (i.e., a participant's lexically-guided random slope for Block was used as a predictor in the distributional learning model, and vice versa). A score of ambiguity acceptance was calculated as the number of ambiguous target words accepted as real words in the lexical decision task (Shift acceptance as in Scharenborg & Janse, 2013), and was standardized and included in the model for individual differences in lexicallyguided learning. Additional measures, including PPVT, TMT, SPIN, digit span and PTA, were converted into z-scores around the mean of their respective age group and included in both models.…”

“…Using both lexically-guided and distributional learning tasks, and a series of cognitive measures, we investigate whether younger and older adults perform differently when lexical status plays a role in exposure and whether individual differences in cognitive measures predict learning in either perceptual learning task. We expect older adults to show comparable learning to younger adults in the lexically-guided learning task (as in Scharenborg & Janse, 2013), but that age may affect learning in the distributional learning task, where no additional lexical information is available, resulting in less learning for the older adults in this task. We further test whether individual differences in several sensory and cognitive factors predict perceptual flexibility in each of these learning tasks, under the assumption that variation in these factors likely influences the amount of perceptual learning in an individual.…”