Cerebral encoding of syntactic-levels in the Mandarin Chinese Left-Periphery: insights from fMRI

Murielle FABRE, INALCO, CRLAO (CNRS UMR 8563, INALCO/EHESS) & Collège de France - Chaire de Psychologie cognitive expérimentale & Cognitive Neuroimaging Unit of INSERM U992 (UNICOG, NeuroSpin – CEA)

In the last two decades, a variety of approaches using brain-imaging methods have sought to characterize the regions implicated in syntactic processes to reveal part of the neural organization of language, a key issue for the origins and development of human language. Recent quantitative neuropsychological data have proven to support the linguistic hypothesis that words in a sentence are combined into hierarchical structures, pinpointing a perisylvian network of regions - encompassing inferior frontal regions and temporal ones - implied in the sentence structure processing (Pallier et al., 2011). However, the detailed view of which brain region codes for the different aspects of the sentence structure, and how the human brain computes and represents syntactic structures remain two open questions.

The actual state of the art is compelling researchers to deepen their understanding of the cerebral encoding of the different levels of linguistic representation and of the complexity parameters of sentence tree structure. Sentence hierarchical structure building is questioned by investigating experimentally the encoding of syntactic representation of the Chinese Left-Periphery and of syntactic movement. The central point of the current fMRI experiment (functional Magnetic Resonance Imaging study with 20 Mandarin native speakers), is that sentence domains including sentence Left-Periphery (e.g. [CP [IP [VP]]]) might be an important complexity parameter to be considered in order to understand sentence cerebral encoding.

Previous typological and formal research on the syntax of the Mandarin Left-Periphery (see Topic and Focus literature : Badan 2008 ; Badan & Del Gobbo 2011 and 2015 ; Paul 2002, 2005, 2015 ; Shyu 1995 and 2001, and others) offers rich testing hypothesis to focus on the processing and cerebral encoding of the syntactic representation-levels present in Topic-Comment articulation, Focus, and more particularly on the properties of the sentence-initial Topic field, and on the contrastive interpretation of preposed objects.

Chinese Topic-Comment articulations are in fact the ideal testing-ground to investigate sentence hierarchical structure without the presence of overt functional elements (i.e. topic heads, although Mandarin Chinese might have some) and to investigate Topic-Comment articulations that are not generated through syntactic movement (i.e. Left-Dislocation/Topicalisation in condition c6 vs. Base-Generation for sentences with no movement analysis in conditions c2, c3, c4, see Table 1). Not only is the prevalence of Topic-Comment structures a typological very distinctive feature of Mandarin Chinese, but it was also shown that young children in the early stages of syntax acquisition have the ability to distinguish between the notions of subject and topic (Chien, 1983). Moreover, from a more formal point of view the traditionally labeled topic-prominence parameter can be reinterpreted by admitting that in the T-C articulation Topic projection’s functional head is not filled by movement, but via an other syntactic process, namely External Merge (i.e. Base-Generation).

The issue of the informational value of topic is addressed by comparing brain activation for Scene-Setting Topic condition (c3) where the first DP plays the role of an adverbial frame localizing the following Comment clause, with (c2) and (c1) SVO Baseline conditions, which differ minimally in terms of lexical material (i.e. contrast c3/c2 > c1 only the first NP differs, see Table 1).

Table 1 Detailed experimental design of the fMRI Experiment on Chinese Left-Periphery. The experimental design aims at directly contrasting the brain activation related to these eight conditions.

In addition to the previous contrasts, this experiment also attempts to tackle the broader question of the cerebral encoding of dependency links inside the sentence that has undergone syntactic movement transformations. This dependency can be achieved by overt or non-overt linguistic means, and Chinese offers an interesting and particular configuration where animacy gives rise to a more or less overt realization of the object constituent in the Comment clause, preserving the same surface word order. The very minimal contrast between c4 condition and c5 (see Table 1) allows to observe the difference between a coreference link achieved by means of an overt Resumptive (c4), Base-Generated Topic with resumptive [O_iSV + resumptive_i] or by a non-overt linguistic mean in (c5), a trace [O_iSV + trace_i], i.e. [Topic_i + S + V + trace_i].

Chinese left-periphery properties present also the opportunity to obtain a contrastive interpretation without moving constituents to the Left-Periphery: in cases of sentence-internal lian-Focus (c8) and of preposed object (c7). Namely, this property allows the decorrelation of pragmatic and contrastive interpretation from the position in the Left-Periphery: c7 and c8 have a strong Pragmatic and contrastive interpretation without being moved to the LP.

Group-level analyses reveal different brain maps for the above cited different contrasts. Interestingly, Broca subpart Pars Triangularis is involved in the processing of Topic-Comment vs. SVO baseline (c2 > c1), Temporal Pole and Inferior Frontal Gyrus are involved in Object fronting through topicalisation, Base generation vs. A-bar movement to the Left-Periphery elicit a different set of brain areas (see Figure 1), and, last but not least, contrastiveness feature and lian-Focus elicit among other areas also posterior Superior Temporal Sulcus (pSTS) activations.

Figure 1 Base generation vs. A-bar movement to the Left-Periphery elicit a different set of brain areas.

To conclude, leveraging on fine-grained linguistic analyses of the Chinese Left-Periphery – both from typological and formal perspective – the present pluridisciplinary approach aims at investigating experimentally through neuro-imaging techniques the issue of the cerebral representation of Topic and Focus in Mandarin Chinese and of the hierarchical organization of sentence in the Left-Periphery.