Poster B43, Tuesday, August 20, 2019, 3:15 – 5:00 pm, Restaurant Hall
Lists with and without syntax: MEG effects of syntactic composition when local conceptual combination is controlled
Ryan Law1, Liina Pylkkänen1,2,3;1NYUAD Institute, New York University Abu Dhabi, 2Department of Psychology, New York University, 3Department of Linguistics, New York University
INTRODUCTION Constructing complex meanings requires the language system to syntactically and semantically combine smaller pieces into larger structures. The neurobiology of syntactic composition remains challenging to study largely due to its tight link with semantic composition. Specific contributions of different subregions within the combinatorial language network remain unclear. Some argue that lexical and syntactic representations are not dissociable, at least in hemodynamic responses (Fedorenko et al., 2012). Recent MEG findings implicate the posterior temporal lobe for syntactic composition as evidenced by cases in which local conceptual combination occurs in both conditions but syntactic merge only in one (Flick & Pylkkänen, 2018). Here we employed the reverse approach to controlling semantics: our stimuli were void of local conceptual combination but only in one condition did the stimuli participated in a syntactic tree. To achieve this, we measured the MEG activity elicited by (i) lists of nouns that occur inside a sentence, and thus participate in the syntax of that sentence, vs. (ii) the same lists embedded inside longer lists. Crucially, the members of the critical lists do not conceptually compose with each other in either case, allowing for a better than usual control of semantics. DESIGN Stimuli were presented visually via RSVP. We embedded lists of three nouns within sentences or within longer lists. Additionally, we varied the level of semantic association (calculated as Latent Semantic Analysis scores) among the members of the lists, to contrast effects of syntax with effects of semantic association: SENTENCE-HIGHASSOC: The music store sells pianos violins guitars drums and clarinets. LIST-HIGHASSOC: theater graves drums mulch pianos violins guitars crates knuckles cocoas SENTENCE-LOWASSOC: The eccentric collector hoarded lamps dolls guitars watches and shoes. LIST –LOWASSOC: forks pen toilet rodeo lamps dolls guitars wood symbols straps Each trial contained a memory probe task to encourage participants to pay attention. RESULTS Participants took longer to recall words drawn from a list-inside-list than list-inside-sentence. Despite recall being more effortful in the list-inside-list conditions, we observed consistent neural activity increases for list-inside-sentence conditions in several regions, often with sustained timing. Here we report on effects observed on the third member of the list, i.e, “guitars” above. On this item, cluster-based permutation tests on left hemisphere ROIs showed greater activity at (i) ~360-385ms in the anterior temporal lobe, (ii) ~400-440ms in the middle temporal lobe, and (iii) ~35-60ms in the temporo-parietal junction/angular gyrus. Trending effects emerged at ~50-70ms in the posterior temporal lobe. Semantic association did not affect behavioral responses and only elicited trends in ROI activity. CONCLUSION Our results show that, for lexically identical three-member strings, syntactic composition in the absence of local conceptual combination results in activity increases in a distributed network of temporo-parietal regions, including the anterior and middle temporal lobe as well as the temporo-parietal junction/angular gyrus, from which the middle temporal lobe showed the most reliable effect. While an explanation in terms of the global semantics of the sentences cannot be ruled out, explanations in terms of local semantic composition can.
Themes: Syntax, Meaning: Combinatorial Semantics
Method: Electrophysiology (MEG/EEG/ECOG)