Meaning in the Brain by Baggio Giosuè

Author:Baggio, Giosuè
Language: eng
Format: epub
Tags: semantics; visual perception; electrophysiology; brain networks; referential processing; elaborative processing
Publisher: MIT Press

6

Discourse Models as Cortical Stable States

The main purpose of a neural theory of meaning is to explain experimental data and predict further observations, at present available in the form of correlations between classes of stimuli and classes of brain responses. An additional goal of the I-system theory is consistency with the fact that discourse meaning reaches conscious awareness. That is not necessarily the case with relational structures. Understanding discourse typically requires being aware of the model’s content. Building on Johnson-Laird’s distinction between propositional representations and mental models, I have argued that, in most cases, interpretation exceeds the computational capacity of the R-system. The binding problem in semantics can be addressed by assuming bottom-up binding operations on amodal conceptual representations (within SS1 in the R-system) and top-down binding operations on lexical interface codes (in SS2). However, comprehension may occur only if tokens, linked to lexical semantic types by the R-system during binding, are in turn interpreted and, more precisely, linked to representations of referents. The speaker’s communicative intentions may have to be recognized, and inferences from discourse may have to be drawn, before meaning is recovered completely. These referential, elaborative, and inferential operations are all executed by the I-system. In chapter 5, I presented direct experimental evidence that the R- and I-systems are functionally separable. The I-system builds a minimal or a partial discourse model based on the relational structures generated and maintained by the R-system. Interpretive processing occurs in a post-N400 time window and recruits brain areas other than LIFG, LATL, and pMSTG. This chapter extends the cycle model, put forward in chapter 3, to account for these facts.

A neural theory of the I-system should be compatible with the computational and algorithmic analyses of interpretation presented in chapter 4. In particular, the theory should specify what discourse models correspond to in neural terms, in addition to mapping discourse processes in brain space and time. The theory must also be consistent with R-system principles (e.g., autonomous semantics) and further I-system principles (e.g., synchronous incrementality). Finally, the I-system theory should explain and possibly predict instances of the following phenomena, which together constitute the theory’s explanandum:

(P1) The SAN differs from the N400 in its time course and scalp distribution. It is observed when additional (re)computations are carried out on discourse models, in the presence of (co)referential ambiguity, during the construction of complex reference structures, and when implicatures or logical inferences (e.g., deduction) are (with)drawn.

(P2) γ bursts have been observed in response to referentially coherent stimuli relative to referentially ambiguous stimuli. These γ responses originate in the left parietal cortex (400-600 ms post-stimulus) and in the left fronto-temporal cortex (500-1000 ms).

(P3) The left inferior parietal lobule (IPL) and adjacent parietal regions (e.g., the left IPS) are activated by processing numerical quantifiers, by deductive reasoning, and during the construction and evaluation of multiple models.

(P4) The medial prefrontal cortex (mPFC) and neighboring cingulate regions are activated by stimuli that trigger pragmatic inferences (implicatures), such as quantifiers (e.g., ‘some’), indirect replies, and novel metaphors.

(P5) The middle frontal

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