Poster Slam Session D, Wednesday, August 21, 2019, 5:00 - 5:15 pm, Finlandia Hall, Emily Myers
Neuromagnetic evoked responses to unattended speech as indices of language processing in young adults and in healthy aging
Rasha Hyder1, Andreas Højlund1, Mads Jensen1, Karen Østergaard2, Yury Shtyrov1;1Center of Functionally Integrative Neuroscience (CFIN), Aarhus University, 2Department of Neurology, Aarhus University Hospital (AUH)
Assessing the brain activity related to language comprehension is required in a range of situations (e.g. clinical or developmental assessment). Particularly in cases when the subjects’ cooperation with instructions cannot be guaranteed (e.g., to neurological conditions, disability etc.), a protocol is needed that could evaluate the neurocognitive status of the language system independently from overt attention and behavioural tasks. To scrutinise the functioning of language neural circuits without relying on focussed attention and behavioural responses, we designed a novel paradigm which allows quantifying a range of neurolinguistic processes by recording the brain’s automatic responses to different speech sounds with carefully manipulated linguistic properties. This procedure is carried out using magnetoencephalography (MEG) combined with individual MR images to guide the source reconstruction of the event-related brain responses. In the first experiment, this paradigm was tested in healthy young participants who were presented with a sequence of speech stimuli, which included meaningful words of different semantic categories, meaningless pseudowords as well as (morpho)syntactically correct and incorrect forms, while focusing on watching a silent movie and ignoring the auditory language input. Meaningful words included action verbs, abstract verbs and concrete nouns. Syntactic word properties were manipulated using counterbalanced word-affix combinations expressing the definiteness of nouns as well as the past participle of the verbs. All stimuli were tightly controlled acoustically and presented equiprobably and pseudorandomly in a short sequence of (~30 minutes). Event-related responses were analysed using minimum-norm source estimates computed on individual MRI-based boundary element models. Permutation tests were employed for assessing the significance of each linguistic contrast in an a priori defined set of language-related cortical areas of the left hemisphere. The results of this experiment validated the applicability of our proposed paradigm for an objective assessment of a range of language functions, including lexical access (visible as enhanced word response vs. pseudoword, reflecting automatic word memory trace activation in the brain), referential semantics (evident through more frontal cortical distribution of responses to action vs. non-action word, likely due to semantically-specific motor cortex involvement) and morphosyntax (asyntactic inflections led to activity increase over syntactically correct forms, indicating grammatical/morphological processing). In our second experiment, this paradigm was applied to healthy elderly participants. The results from elderly group revealed a range of effects of aging on different levels of linguistic processing: reduced, delayed and topogprahically shifted lexico-semantic ERFs and fully absent correlates of automatic syntactic parsing. In conclusion, the results from both healthy groups indicate that the new paradigm may be a subject-friendly and time-efficient tool to test multiple language comprehension processes in the brain in the absence of attention on the linguistic input or any stimulus-related tasks, which makes it potentially applicable for assessing neurolinguistic status of individuals/patients who are unable to comply with an active behavioural assessment protocol. We will discuss implications of this approach to the study of neurolinguistics processing in healthy ageing and in neurological conditions.
Themes: Speech Perception, Methods
Method: Electrophysiology (MEG/EEG/ECOG)
Poster D79