Dissociating Effects of Scrambling and Topicalization within the Left Frontal and Temporal Language Areas: An fMRI Study in Kaqchikel Maya

Some natural languages grammatically allow different types of changing word orders, such as object scrambling and topicalization. Scrambling and topicalization are more related to syntax and semantics/phonology, respectively. Here we hypothesized that scrambling should activate the left frontal regions, while topicalization would affect the bilateral temporal regions. To examine such distinct effects in our functional magnetic resonance imaging study, we targeted the Kaqchikel Maya language, a Mayan language spoken in Guatemala. In Kaqchikel, the syntactically canonical word order is verb-object-subject (VOS), but at least three non-canonical word orders (i.e., SVO, VSO, and OVS) are also grammatically allowed. We used a sentence-picture matching task, in which the participants listened to a short Kaqchikel sentence and judged whether a picture matched the meaning of the sentence. The advantage of applying this experimental paradigm to an understudied language such as Kaqchikel is that it will allow us to validate the universality of linguistic computation in the brain. We found that the conditions with scrambled sentences [+scrambling] elicited significant activation in the left inferior frontal gyrus and lateral premotor cortex, both of which have been proposed as grammar centers, indicating the effects of syntactic loads. In contrast, the conditions without topicalization [-topicalization] resulted in significant activation in bilateral Heschl’s gyrus and superior temporal gyrus, demonstrating that the syntactic and phonological processes were clearly dissociated within the language areas. Moreover, the pre-supplementary motor area and left superior/middle temporal gyri were activated under relatively demanding conditions, suggesting their supportive roles in syntactic or semantic processing. To exclude any semantic/phonological effects of the object-subject word orders, we performed direct comparisons while making the factor of topicalization constant, and observed localized activations in the left inferior frontal gyrus and lateral premotor cortex. These results establish that the types of scrambling and topicalization have different impacts on the specified language areas. These findings further indicate that the functional roles of these left frontal and temporal regions involve linguistic aspects themselves, namely syntax versus semantics/phonology, rather than output/input aspects of speech processing

言語野における文法の計算原理 : fMRIによる統辞操作の検証

学位の種別:課程博士University of Tokyo(東京大学

連濁の生起率に基づく日本語複合語の分類 : 連濁データベースによる研究

山口大学東京大学Yamaguchi UniversityThe University of Tokyo連濁はもっとも広く知られた日本語の音韻現象の1つである。先行研究では，日本語の複合語は連濁の生起率の違いに基づいて，いくつかのグループに分類されることが提案されている。しかしながら先行研究では，連濁生起率の分類基準が恣意的であった点，またグループの数をあらかじめ仮定していた点に問題があった。そこで本研究では，混合正規分布モデルに基づくクラスター分析と連濁データベース（Irwin and Miyashita 2015）を用いて，日本語複合語を分類する際の最適な分類基準とクラスター数を検討した。複合名詞と複合動詞のどちらも，2つのクラスターを仮定したモデルが最適であり，クラスター同士の分類基準は，複合名詞では連濁生起率が90%，複合動詞では40%であった。これらの結果は先行研究のクラスター数や分類基準とは異なるものであった。我々の結果は，モデルに基づくクラスター分析が言語データに対する最適な分類を行う上で非常に有効であることを示すものである。Rendaku is one of the most well-known phonological phenomena in Japanese, which voices the initial obstruent of the second element of a compound. Previous studies have proposed that Japanese compound words can be classified on the basis of the frequency of rendaku (rendaku rate). However, since these studies used arbitrary criteria to determine clusters, such as 33% and 66%, as well as arbitrary numbers of clusters, it is crucial to examine the plausibility of such criteria. In this study, we examined the optimal boundary criteria as well as the optimal number of clusters using a clustering analysis based on Gaussian mixture modeling and the Rendaku Database (Irwin and Miyashita 2015). The cluster analyses clarified that the two-cluster model was optimal for classifying both compound nouns and compound verbs. The boundary values of the rendaku rate for these clusters were approximately 90% and 40% for the compound nouns and compound verbs, respectively. These results were inconsistent with the findings of previous studies. Our findings demonstrate that model-based clustering analysis is an effective method of determining optimal classification of linguistic data

Dissociating the processing of empty categories in raising and control sentences: A self-paced reading study in Japanese

[This is a preprint version of the manuscript. It is now published: https://doi.org/10.3389/flang.2023.1138749. Please cite the published version.] Theoretical linguistics has proposed different types of empty categories (ECs), i.e., unpronounced words with syntactic characteristics. ECs are a key to elucidating the computational system of syntax, algorithms of language processing, and their neural implementation. Here we examined the distinction between raising and control sentences in Japanese and whether ECs are psychologically real. We found two striking results by using a self-paced reading and a probe word recognition priming technique. First, we demonstrate that the reading times of raising and control sentences in Japanese were better explained by the linear mixed-effects model considering the differences of ECs, i.e., Copy and PRO. Secondly, we found a significant reactivation effect for raising and control sentences, which have ECs, and reflexive sentences without ECs. These results indicate that ECs are processed similarly to reflexive pronouns (e.g., himself). Based on these results, we conclude that raising and control sentences in Japanese have different ECs, i.e., Copy and PRO, and that ECs have psychological reality. Our results demonstrate that behavioral experiment based on theoretical linguistics, which is the first step for developing linking hypotheses connecting theoretical linguistics and experimental neuroscience, is indeed necessary for testing hypotheses proposed in theoretical linguistics

Regions related to the sentence conditions and/or string conditions.

<p>Regions related to the sentence conditions and/or string conditions.</p

Syntactic Computation in the Human Brain: The Degree of Merger as a Key Factor

<div><p>Our goal of this study is to characterize the functions of language areas in most precise terms. Previous neuroimaging studies have reported that more complex sentences elicit larger activations in the left inferior frontal gyrus (L. F3op/F3t), although the most critical factor still remains to be identified. We hypothesize that pseudowords with grammatical particles and morphosyntactic information alone impose a construction of syntactic structures, just like normal sentences, and that “the Degree of Merger” (DoM) in recursively merged sentences parametrically modulates neural activations. Using jabberwocky sentences with distinct constructions, we fitted various parametric models of syntactic, other linguistic, and nonlinguistic factors to activations measured with functional magnetic resonance imaging. We demonstrated that the models of DoM and “DoM+number of Search (searching syntactic features)” were the best to explain activations in the L. F3op/F3t and supramarginal gyrus (L. SMG), respectively. We further introduced letter strings, which had neither lexical associations nor grammatical particles, but retained both matching orders and symbol orders of sentences. By directly contrasting jabberwocky sentences with letter strings, localized activations in L. F3op/F3t and L. SMG were indeed independent of matching orders and symbol orders. Moreover, by using dynamic causal modeling, we found that the model with a inhibitory modulatory effect for the bottom-up connectivity from L. SMG to L. F3op/F3t was the best one. For this best model, the top-down connection from L. F3op/F3t to L. SMG was significantly positive. By using diffusion-tensor imaging, we confirmed that the left dorsal pathway of the superior longitudinal and arcuate fasciculi consistently connected these regions. Lastly, we established that nonlinguistic order-related and error-related factors significantly activated the right (R.) lateral premotor cortex and R. F3op/F3t, respectively. These results indicate that the identified network of L. F3op/F3t and L. SMG subserves the calculation of DoM in recursively merged sentences.</p> </div

Estimates of nonlinguistic and syntactic factors to account for activations.

<p>For Nested, Simple, Reverse, and Same, the estimates for short and long stimuli were added together, because each factor’s unit load would be invariable between short and long stimuli under each of the sentence and string conditions. Because the matching orders or symbol orders were identical between the Nested and Reverse conditions, the unit load of memory span or counting was invariable between the Nested and Reverse conditions, which was also invariable between the Reverse and Same conditions, thus invariable among the Nested, Simple, Reverse, and Same conditions. For brevity, the contrasts of [Nested – Simple] and [Reverse – Same] are denoted with a double prime mark, i.e., Nested” and Reverse”, respectively. Note that the estimates of memory span in Nested” and Reverse” also became identical, and that the Reverse” contrast makes the listed estimates null, except memory span. The last two syntactic factors, whose models were best in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056230#pone-0056230-t005" target="_blank">Table 5</a>, consistently accounted for the results of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056230#pone-0056230-g004" target="_blank">Figure 4F</a>. All estimates of the other factors unlisted here were null in Reverse”, which cannot account for the results of <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0056230#pone-0056230-g005" target="_blank">Figure 5C and 5D</a>.</p