Electrophysiological correlates of syntactic structures

Abstract

Syntax is traditionally defined as a specifically human way to pair sound with meaning: words are assembled in a recursive way generating a potentially infinite set of sentences 1,2 . There can be different phrasal structures depending on the types of words involved, for example, "noun phrases" (NP), combining an article and a noun, vs. "verb phrases" (VP), combining a verb and a complement. Although it is known that the combination of an increasing number of words in sequences correlates with an increasing electrophysiological activity 3,4 , the specific electrophysiological correlates of the syntactic operation generating NPs vs. VPs remain unknown. A major confounding factor is the fact that syntactic information is inevitably intertwined with the acoustic information contained in words even during inner speech 5 . Here, we addressed this issue in a novel way by designing a paradigm to factor out acoustic information and isolate the syntactic component. In particular, we construed phrases that have exactly the same acoustic content but that are interpreted as NPs or VPs depending on their syntactic context (homophonous phrases). By performing stereo-electro-encephalographic (SEEG) recordings in epileptic patients 6 we show that VPs are associated with a higher activity in the high gamma band (150-300Hz frequency), an index of cortical activity associated with linguistic processing, with respect to NPs in multiple cortical areas in both hemispheres, including language areas and their homologous in the nondominant hemisphere. Our findings pave the way to a deeper understanding of the electrophysiological mechanisms underlying syntax and contribute to the ultimate far reaching goal of a complete neural decoding of linguistic structures from the brain 2 .Factoring sound out of a linguistic expression is a major empirical problem, since sound is inevitably intertwined with syntactic information 3,7 even during inner speech 5 . By crucially relying on Italian grammar we designed a novel protocol to circumvent this problem and measure the specific electrophysiological correlates of two basic syntactic structures. The stimuli were pairs of different sentences containing strings of two words with exactly the same acoustic information but completely different syntax (homophonous strings). More specifically, each pair contained an NP, resulting from syntactic combination of two lexical elements (a definite article and a noun), and a VP, resulting from the syntactic combination of two different types of lexical elements (a verb and a pronominal complement): the NP and the VP were pronounced in exactly the same way. In addition, each VP included a further crucial difference: the object of the verb, realized as a pronoun, was moved from its canonical position on the right of the verb to the left of the verb, a syntactic operation called "cliticization". For example, the sequence [laˈpɔrta], could be interpreted either as a noun phrase ("the door") or a verb phrase ("brings her"; lit.: her brings) depending on the syntactic ...

The timing versus resource problem in nonnative sentence processing: Evidence from a time-frequency analysis of anaphora resolution in successive wh-movement in native and nonnative speakers of French

“…A growing body of research [ 29 , 35 – 42 ] establishes ERSPs entrained by phonetic properties in the auditory cortex, as well as ERSPs due to internal neurocognitive processes without external entrainment. In sentence comprehension, increased high gamma (150-300Hz) activity has been found to relate to phrase-structure building [ 43 , 44 ] in terms of association of items and compositional interpretation [ 29 ]. In anaphora, the retrieval of a congruent antecedent from memory induces greater gamma power than in cases of antecedent ambiguity or mismatch [ 45 ; see also 46 ].…”