Lexicon and Syntax: Complexity across Genres and Language Varieties
Authors: Pietro dell’Oglio, Dominique Brunato, Felice Dell'Orletta (Università di Pisa, CNR-ILC, 2018)
Topic: Lexical and Semantic Resources and Analysis

Abstract
This paper presents ﬁrst results English. This paper presents ﬁrst results of an ongoing work to investigate the interplay between lexical complexity and syntactic complexity with respect to nominal lexicon and how it is affected by textual genre and level of linguistic complexity within genre. A cross-genre analysis is carried out for the Italian language using multi–leveled linguistic features automatically extracted from dependency parsed corpora.

Introduction
Linguistic complexity is a multifaceted notion which has been addressed from different perspectives. One established dichotomy distinguishes a “global” vs a “local” perspective, where the former considers the complexity of the language as a whole and the latter focuses on complexity within each sub-domains, i.e. phonology, morphology, syntax, discourse (Miestamo, 2008). While measuring global complexity is a very ambitious and probably hopeless endeavor, measuring local complexities is perceived as a more doable task (Kortmann and Szmrecsanyi, 2012). The level of complexity within each subdomains indeed has been formalized in terms of distinct parameters that capture either internal properties of the language (in the “absolute” notion of complexity) or phenomena correlating to processing difﬁculties from the language user’s viewpoint (in the “relative” notion of complexity) (Miestamo, 2008). For instance, complexity at lexical level has been computed in terms of length (measured in characters or syllables), of frequency either of the whole surface word (Randall and Wayne, 1988; Chiari and De Mauro, 2014) or of its internal components (see e.g. the root frequency effect (Burani, 2006)), ambiguity and familiarity, among others. At syntactic level, much attention has been paid on canonicity effects due to word order variation (Diessel, 2005; Hawkins, 1994; Futrell et al., 2015), as well as on long-distance dependencies (Gibson, 1998; Gibson, 2000) proving their effect on a wide range of psycholinguistic phenomena, such as the subject/object relative clauses asymmetry or the garden path effect in main verb/reduced–relative ambiguities. An interesting question addressed by recent corpus-driven research is how language complexity is affected by textual genre. At syntactic level, the study by Liu (2017) on ten genres taken from the British National Corpus showed that genrespeciﬁc stylistic factors have an inﬂuence on the distribution of dependency distances and dependency direction. Similarly for Italian, Brunato and Dell’Orletta (2017) investigated the inﬂuence of genre, and level of complexity within genre, on a range of factors of syntactic complexity automatically computed from dependency-parsed corpora. Inspired by that work, we also intend to analyze the effect of genre on linguistic complexity. However, unlike the dominant local approach, where each subdomain is typically studied in isolation, our contribution intends to address the interrelation between different levels, i.e. lexicon and syntax. Speciﬁcally, we investigate the following questions: • to what extent is lexical complexity inﬂuenced by genre? • to what extent is lexical complexity inﬂuenced by the level of complexity within the same genre? • is there a correlation between lexical complexity and syntactic complexity? Does it vary according to genre and level of complexity within the same genre? To answer these questions, we conducted an indepth analysis for the Italian language based on automatically dependency parsed corpora aimed at assessing i) the distribution of simple and complex nominal lexicon in different genres and different language varieties for the same genre ii) the syntactic role bears by “simple” and “complex” nouns characterizing each corpus iii) the correlation between “simple” and “complex” nouns with features of complexity underlying the syntactic structure in which they occur. In what follows we ﬁrst describe the corpora considered in this study. We then illustrate how lexical and syntactic complexity have been formalized. In Section 4 we discuss some preliminary ﬁndings obtained from the comparative investigation across corpora.

Conclusion
While language complexity is a central topic in linguistic and computational linguistics research, it is typically addressed from a local perspective, where each subdomain is investigated in isolation. In this preliminary work, we have deﬁned a method to study the interplay between lexical and syntactic complexity restricted to the nominal domain. We modeled the two notions in terms of frequency, with respect to lexical complexity, and of a set of parse tree features formalizing phenomena of syntactic complexity. Our approach was tested on corpora selected to be representative of different genres and different levels of complexity within each genre, in order to investigate whether noun complexity differently affects syntactic complexity according to the two dimensions. We observed e.g. that nouns tend to appear closer to the root in simple language varieties, independently from genre, while the effect of genre and linguistic complexity is less sharp with respect to the other considered features. To have a deeper understanding of the observed tendencies we are currently carrying out a more in depth analysis focusing on ﬁne-grained features of syntactic complexity, such as the depth of the nominal subtree. Further, we would like to enlarge this approach to test other constituents of the sentence, such as the verb.