Abstract:

The accurate perception of lexical tones in Mandarin Chinese is an important foundation for successfully understanding spoken Chinese. Previous behavioral studies have shown that the ability to perceive lexical tones in Mandarin declines in elderly individuals. In addition to other research areas related to language and aging, the central issue in phonetic perception during aging concerns whether perceptual changes related to aging are area-specific or area-general. The area-general language hypothesis of aging assumes that changes in language perception related to aging are caused by a decline in both general sensory perception function and high-order cognitive function. In contrast, the area-specific language hypothesis of aging assumes that changes in aging-related language perception are caused by specific deficits in language processing. Previous studies mostly detected the state of attention and focused on how area-general factors affect the processing of segmental phonemes in elderly individuals. The present study examined neurophysiological responses, particularly that of MMN, to explore whether the aging of lexical tone perception is language-specific for Mandarin.
The current study recruited 22 healthy elderly participants (age range: 55.6~79.6 years) and 18 young participants (age range: 22.7~29.0 years). In a passive oddball task, we used event-related potentials (ERPs) to examine Mandarin lexical tone perception. Three syllables from a lexical tone continuum were chosen as stimuli to form an across-category stimulus pair and a within-category stimulus pair for the ERP oddball task. A non-speech stimulus pair was generated on the basis of the within-category stimulus pair. During the experiment, participants were instructed to ignore the presented sounds while watching a self-selected movie.
ERP data showed that in the across-category condition, compared with the young group, the elderly group had a smaller MMN, and there was no between-group difference in the within-category condition. In the young group, a non-speech tone elicited a larger MMN amplitude than a speech tone that shared the same pitch contour, while the elderly group did not show a speech enhancement effect. In addition, compared with that of the young group, the amplitude of the MMN elicited by the non-speech contrast in the elderly group was significantly smaller. The results indicated that the general decline in central auditory processing function was not related to the pre-attention processing of lexical tone. In addition, when the level at which the auditory input stimulus could be sensed was controlled according to peripheral hearing abilities, the decline in peripheral auditory function was not related to the preservation of or decline in lexical tone perception in the current study.
In the current study, there is no evidence that the age-related decline in area-general factors affects tone perception in the pre-attention condition. On this basis, this study further speculated that the ability of elderly Mandarin-speaking individuals to perceive lexical tone in pre-attention conditions was preserved and only declined for specific languages, and the above-mentioned decline in the processing of knowledge of Mandarin tone category and the wider preservation of the processing of speech tones are language-specific. The present study provides evidence for the area-specific language hypothesis of aging.

Key words: Mandarin, aging, lexical tone category, pre-attention, area-specific