Categorical Perception of Lexical Tones in Mandarin-Speaking Seniors.

PURPOSE: This study aims to investigate the different degeneration processes of categorical perception (CP) of Mandarin lexical tones in the normal aging population and the pathological aging population with mild cognitive impairment (MCI). METHOD: In Experiment I, we compared the identification and discrimination of Tone 1 and Tone 2 across young adults, seniors aged 60-65 years, and older seniors aged 75-80 years with normal cognitive abilities. In Experiment II, we compared lexical tone identification and discrimination across young adults, healthy seniors, and age-matched seniors with MCI. RESULTS: In Experiment I, tone perception was intact in seniors aged below 65 years. Those aged above 75 years could also maintain normal tone identification, whereas they showed poorer tone discrimination correlated with age-related poorer hearing level. In Experiment II, healthy seniors showed normal CP of Mandarin tones. Tone identification was also normal in those with MCI, whereas their tone discrimination had significantly degenerated. CONCLUSIONS: In the normal aging population, age-related hearing loss decreased signal audibility, accounting for poorer discrimination of Mandarin lexical tones in seniors above 75 years. In the pathological aging population with MCI, the poorer discrimination of lexical tones may be attributed to the additive effect of age, hearing loss, and cognitive impairment (e.g., impaired working memory and long-term phonological memory). This study uncovered the roles of low-level sensory processing and high-level cognitive processing in lexical tone perception in the Chinese aging population.

The effect of Mandarin listeners' musical and pitch aptitude on perceptual learning of Cantonese level-tones.

Contrary to studies on speech learning of consonants and vowels, the issue of individual variability is less well understood in the learning of lexical tones. Whereas existing studies have focused on contour-tone learning (Mandarin) by listeners without experience of a tonal language, this study addressed a research gap by investigating the perceptual learning of level-tone contrasts (Cantonese) by learners with experience of a contour-tone system (Mandarin). Critically, we sought to answer the question of how Mandarin listeners' initial perception and learning of Cantonese level-tones are affected by their musical and pitch aptitude. Mandarin-speaking participants completed a pretest, training, and a posttest in the level-tone discrimination and identification (ID) tasks. They were assessed in musical aptitude and speech and nonspeech pitch thresholds before training. The results revealed a significant training effect in the ID task but not in the discrimination task. Importantly, the regression analyses showed an advantage of higher musical and pitch aptitude in perceiving Cantonese level-tone categories. The results explained part of the level-tone learning variability in speakers of a contour-tone system. The finding implies that prior experience of a tonal language does not necessarily override the advantage of listeners' musical and pitch aptitude.

Conflict monitoring in multi-sensory flanker tasks: Effects of cross-modal distractors on the N2 component.

The N2 component is a well-known neural correlate of conflict monitoring (CM), being more negative in the presence of conflicting information in visual conflict tasks. However, whether to-be-ignored auditory distractors can introduce additional conflict remains unknown. In the present work, subjects performed a visual (V) and audiovisual (AV) version of a Go/NoGo flanker task, and responded only if the target arrow pointed toward a pre-specified direction (e.g., left). In the AV task, in which to-be-ignored auditory distractors that were semantically associated with the flankers were concurrently presented, the congruency effect on both RT and N2 amplitude was enhanced, confirming that additional conflict can be brought about by cross-modal distractors at both behavioural and neural levels. Consistent with the hypothesis that N2 amplitude reflects response conflict in visual conflict tasks, within-subject correlation between N2 amplitude and RT was significant in the Go conditions for the V task (congruent/incongruent). However, for the AV task, the correlation was significant only in the congruent condition. These findings suggest that while the cross-modal conflict is registered by the CM process, only part of this conflict could effectively induce response conflict.