| The context is important for perception of speech sounds.Previous studies generally prove the effect of shifting contexts’ mean F0 on tonal perception.However,different schools have not reached a consistent conclusion on whether the mechanism of contextual effect is the mixing of articulatory movements resulting from coarticulation,or the difference in the acoustic properties of the contextual and target sounds magnified by the auditory system.Furthermore,existing research has mainly been restricted to performance of the young generation under a quiet listening condition,and few has focused on whether and how senescence and complex listening conditions interact with context effects.Based on the identification task,this study compared the perception of tones with a preceding context by three groups(young,middle-aged and old listeners with mild cognitive impairment(MCI))under quiet and noisy listening conditions.The following research questions were explored:1)How do aging and MCI affect the categorical perception of isolated Mandarin T1-T2?2)How do aging and MCI influence the extrinsic context effect on normalization of Mandarin T1/T2?3)How do aging and MCI interact with noisy conditions to impact the context effect on normalization of Mandarin T1/T2?With normal hearing,young(n=19),middle-aged(n=19),and old(n=18)people with MCI were tested on two tasks,in which participants were required to identify a tonal category with and without a speech context.The target stimuli were from a continuum of Mandarin T1T2,and the identification task with a context was conducted in a quiet environment and babble noise with signal-to-noise ratios(SNRs)set at 5 and 0 dB.The experimental presentation and data collection were conducted in E-prime 2.0 and all the data were analyzed with R 4.1.1.Main findings are summarized as follows:1)For the first task,participants were asked to identify tones in isolation,and no significant difference in boundary positions among the three groups was observed,indicating that ambiguous stimuli of the continuum for the three groups were the same.However,there was a marginally significant difference in the boundary widths between the young and old group,which might be ascribed to the cognitive situation and decayed phonetic short-term memory of the elderly.2)As for the identification of ambiguous tonal stimuli with a preceding context,the context effect worked in a quiet environment,and the size and manner of the effect were nearly the same for the three groups.In other words,when the average F0 of the context was increased,responses of listeners to the target tone were prone to a low level one with lower F0 and vice versa.Rich language experience and over-recruitment of certain brain regions not employed by younger listeners could compensate for old people’s physiological degeneration and cognitive impairment,such that they might also achieve a size of the context effect comparable to the young.3)For the identification task in noisy conditions,however,irrespective of different SNRs,the context exerted little influence on listeners’ perception of target tones.Results generally showed that in a quiet listening condition,external cues extracted from the context contrastively affected three groups’ tone normalization to the same extent.Nevertheless,despite SNRs,noise eliminated such an effect.These findings show that context effects on tone normalization tend to be susceptible to babble noise but be immune to the greying process and MCI.It supports the view that the context effect is only a by-product of the mature auditory system.In addition,this study may provide a reference for the chronic problem of how to help the elderly overcome barriers of speech perception and communication. |
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