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Spatiotemporal signature of morphosyntactic planning in English sentence production

Poster Session D, Saturday, September 13, 5:00 - 6:30 pm, Field House

Yi Wei¹, Ciaran Stone¹, L. Robert Slevc¹, Yasmeen Faroqi-Shah¹, Christian Brodbeck²; ¹University of Maryland, College Park, ²McMaster University

Fluent sentence production relies on the precise and timely coordination of content and structure building prior to motor execution, with morphosyntactic planning playing a critical role in this process. While previous research has explored the neural mechanisms underlying morphosyntactic planning using various neuroimaging methods, identifying key brain regions (e.g., Broca’s area, posterior temporal lobe) and the neural timing before word production, the spatiotemporal dynamics of sub-processes of morphosyntactic planning within sentence production remain underexplored. This study addresses this gap by examining the locations and times of brain activity using MEG during sentence production, with a focus on delineating the subcomponents of sentence planning, namely lexical access, inflectional processes (which differ for nouns and verbs), and constituent assembly that lead to successful utterance production. In a novel overt picture naming paradigm, participants saw object or action pictures along with an icon that elicited one of the subcomponent sentence processes: lexical access, inflectional marking (plurals for objects, tense for actions), and constituent assembly (adjective + object or pronoun + action). This approach allows us to decompose different elements of sentence planning. In each trial, participants first viewed a fixation cross for 1000 ms, followed by an object or action picture for 400 ms, and then another fixation cross for 400 ms. Next, an icon was presented for 400 ms, immediately followed by an image serving as a speaking prompt, which cued participants to produce the utterance. Based on data from twenty native English-speaking right-handed neurotypical adults, our results (generated from volume source space vector-valued dipole currents using Hotelling’s T-Square statistics and threshold-free cluster enhancement correction for multiple comparisons) revealed the following: 1) Inflectional suffix and constituent assembly differ in activation time and strength compared to lexical access: Compared to the lexical access condition (“tree”), both the inflectional suffix condition (“trees”) and the constituent assembly condition (“a blue tree”) engaged the inferior frontal gyrus (IFG) around 400 ms after icon onset. Additionally, the inflectional suffix condition (“trees”) showed prolonged activation compared to constituent assembly, while constituent assembly (“a blue tree”) showed stronger left hemisphere activation around 400 ms than the inflectional suffix condition. 2) The combination of tense, inflectional suffix, and constituent assembly engages additional frontal regions: Compared to the lexical access condition (“cook”), the tense + constituent assembly condition (“she will cook”) engaged the IFG at around 400 ms after icon onset and again at around 550 ms. The tense + inflectional suffix + constituent assembly condition (“she cooked”) engaged additional frontal regions at around 800 ms post-icon onset, suggesting a higher cognitive load prior to speech initiation when more subcomponents need to be planned. In sum, we observed distinct spatiotemporal signatures associated with different subcomponents of sentence production, characterized by: 1) Differences in activation timing and strength for inflectional suffix and constituent assembly, separately. 2) Different timing of IFG region engagement when tense is involved. 3) Additional anterior/superior frontal region engagement prior to speech onset time when tense is involved.

Topic Areas: Language Production,