Lists with and without syntax: A new approach to measuring the neural processing of syntax

Abstract

23In the neurobiology of language, a fundamental challenge is deconfounding syntax from semantics. 24Changes in syntactic structure usually correlate with changes in meaning. We approached this 25 challenge from a new angle. We deployed word lists, which are usually the unstructured control in 26 studies of syntax, as both the test and the control stimulus. Three-noun lists (lamps, dolls, guitars) 27 were embedded in sentences (The eccentric man hoarded lamps, dolls, guitars…) and in longer lists 28 (forks, pen, toilet, rodeo, graves, drums, mulch, lamps, dolls, guitars…). This allowed us to perfectly 29 control both lexical characteristics and local combinatorics: the same words occurred in both 30 conditions and in neither case did the list items locally compose into phrases (e.g. 'lamps' and 'dolls' 31 do not form a phrase). But in one case, the list partakes in a syntactic tree, while in the other, it does 32 not. Being embedded inside a syntactic tree increased source-localized MEG activity at ~250-300ms 33 from word onset in the left inferior frontal cortex, at ~300-350ms in the left anterior temporal lobe 34 and, most reliably, at ~330-400ms in left posterior temporal cortex. In contrast, effects of semantic 35 association strength, which we also varied, localized in left temporo-parietal cortex, with high 36 associations increasing activity at around 400ms. This dissociation offers a novel characterization of 37 the structure vs. meaning contrast in the brain: The fronto-temporal network that is familiar from 38 studies of sentence processing can be driven by the sheer presence of global sentence structure, while 39 associative semantics has a more posterior neural signature. 41Running head: NEURAL PROCESSING OF LISTS WITH AND WITHOUT SYNTAX 3 SIGNIFICANCE STATEMENT 42Human languages all have a syntax, which both enables the infinitude of linguistic creativity and 43 determines what is grammatical in a language. The neurobiology of syntactic processing has, however, 44 been challenging to characterize despite decades of study. One reason is pure manipulations of syntax are 45 difficult to design. The approach here offers a perfect control of two variables that are notoriously hard to 46 keep constant when syntax is manipulated: word meaning and phrasal combinatorics. The same noun lists 47 104 MATERIALS AND METHODS 105 Stimuli & Design106We selected concrete English nouns based on the concreteness rating corpus by Brysbaert, Warriner, 107and Kuperman (2014). From this pool, we then selected nouns that are matched in their log frequency 108 from the SUBTLEX-US corpus (Brysbaert & New, 2009). The critical list nouns were changed from 109 their singular form to plural to block potential noun-noun compounding (e.g. lamp doll could form a 110 Running head: NEURAL PROCESSING OF LISTS WITH AND WITHOUT SYNTAX 7 phrase, but lamps dolls could not). These plural nouns were then used to construct our critical three-111 noun lists such as lamps, dolls, guitars. The lexical characteristics are summarized in Table 2....

Left posterior temporal cortex is sensitive to syntax within conceptually matched Arabic expressions

“…Regarding the effect’s locus, our results are in line with previous fMRI 9 , 24 , 25 , lesion 49 , and MEG 8 , 21 , 22 findings implicating the LPTL in syntactic processing. However, they contrast with results from two main sets of studies in recent years.…”

“…We also note that other MEG studies implicating the LPTL in syntactic processing reported earlier (~ 220 ms) 21 and later (~ 350 ms) 22 clusters; however, they used different designs with lengthier stimuli. Insofar as all LPTL effects tap into the same syntactic computations, this could suggest temporal flexibility in syntactic processing.…”

“…We expected ROIs involved in syntactic processing to respond differently to the varying complexity of our conditions: if the ROI is involved in top-down predictions, we expected effects on the first word (the noun), and if it is involved in bottom-up syntactic combinatorics, we expected effects on the second word (the adjective). As to timing, recent MEG studies have shown syntactic effects a few hundred milliseconds after word onset 21 , 22 , so we chose a 100–500 ms test window after word onset.

Figure 2 Results of syntactic effects analysis.

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Comparing predictors of sentence self-paced reading times: Syntactic complexity versus transitional probability metrics

“…Tying in with a growing body of studies on the neurobiological mechanisms underlying syntactic processing (e.g., [26][27][28][29][30]), Uddén et al [31] investigated functional brain activity associated with comprehending sentences varying in LB and RB complexity. They conducted a re-analysis of a functional magnetic resonance imaging dataset from Schoffelen et al [32], where participants (n = 102) read stimulus sentences (n = 360) of varying syntactic complexity.…”

Minimal phrase composition revealed by intracranial recordings

“…In particular, evidence from neuroimaging and lesion-deficit mapping indicates a role for pMTG in syntactic comprehension and production (Matchin and Hickok, 2020), while pSTS has been implicated via iEEG in hierarchical syntactic computations (Nelson et al, 2017). Posterior temporal regions also provide the strongest and most reliable syntax-specific effects when interpreting lists of nouns embedded within sentences compared to such noun lists in isolation (Law and Pylkkänen, 2021). More broadly, pMTG is robustly associated with basic phrase comprehension deficits across a large number of studies.…”