Research Update
Recently, Deputy Researcher Lu Lingxi, in collaboration with Professor Wang Qun from the Neurology Center of Beijing Tiantan Hospital, Capital Medical University, published a research paper titled "Age differentially modulates the cortical tracking of the lower and higher level linguistic structures during speech comprehension" in the international journal "Cerebral Cortex."
In the process of speech comprehension, the mature brain can rapidly segment continuous speech streams into different levels of linguistic units, such as characters, words, phrases, and sentences, and can neurologically track linguistic hierarchy structures at different time scales. Aging is accompanied by a decline in sensory sensitivity and perceptual control, which may affect the brain's processing of speech. However, it remains unclear how aging influences the brain's processing of language structures. To address this question, this study recruited two groups of participants: young native Mandarin Chinese speakers and older individuals. They were exposed to speech stimuli containing three levels of language structures: characters, words, and sentences. These language structures were presented at fixed frequencies of 4 Hz, 2 Hz, and 1 Hz using a frequency-tagging method. Two attention conditions, passive and active, were also set up. The participants' neural activities during speech comprehension were recorded using magnetoencephalography (MEG).
Figure 1: A. Auditory speech stimuli containing three levels of language structures corresponding to frequencies of 4 Hz, 2 Hz, and 1 Hz. B. Schematic diagram of the passive and active attention experimental procedures.
The research found that age exhibits differential modulation in the processing of different language structure levels during speech comprehension. Older individuals show significantly weaker neural tracking of higher-level language units (phrases and sentences) compared to younger individuals. However, their neural tracking of lower-level language units (characters) is significantly stronger than that of younger individuals. Notably, the older individuals' attentional modulation of neural tracking at the sentence level is significantly weaker than that of the younger individuals. Further combined analysis of neural and behavioral data indicates that the enhanced tracking of higher-level language structures and the reduced tracking of lower-level structures in the brain are associated with better behavioral performance. The results suggest that the difficulties older individuals face in speech comprehension may result from the combined effects of enhanced processing of lower-level semantic information, weakened processing of higher-level semantic information, and reduced flexibility in attentional modulation at the sentence level. This research contributes to a deeper understanding of aging-related language processing issues.
Figure 2: Neural tracking activities of language hierarchy structures in the older and younger groups.
Dr. Xu Na, who completed her postdoctoral work at Beijing Tiantan Hospital, Capital Medical University, is the first author of this paper. Deputy Researcher Lu Lingxi from the Base of Cognitive Science and the Neurology Center of Beijing Tiantan Hospital, Capital Medical University, and Professor Wang Qun from the Neurology Center of Beijing Tiantan Hospital, Capital Medical University, are the corresponding authors. This research was supported by the National Key R&D Program of China, the National Natural Science Foundation of China, the Beijing Science and Technology New Star Program, the Beijing Municipal Natural Science Foundation, and the Beijing Municipal Social Science Foundation Youth Program.
Citation:
Xu N, Qin X, Zhou Z, Shan W, Ren J, Yang C, Lu L*, Wang Q*. Age differentially modulates the cortical tracking of the lower and higher level linguistic structures during speech comprehension. Cereb Cortex. 2023 Aug 11:bhad296. doi: 10.1093/cercor/bhad296.
