Lexical Simplification in Foreign Language Learning: Creating Pedagogically Suitable Simplified Example Sentences (2022)

Abstract: This study presents a lexical simplification (LS) methodology for foreign language (FL) learning purposes, a barely explored area of automatic text simplification (TS). The method, targeted at Spanish as a foreign language (SFL), includes a customised complex word identification (CWI) classifier and generates substitutions based on masked language modelling. Performance is calculated on a custom dataset by means of a new, pedagogically-oriented evaluation. With 43% of the top simplifications being found suitable, the method shows potential for simplifying sentences to be used in FL learning activities. The evaluation also suggests that, though still crucial, meaning preservation is not always a prerequisite for successful LS. To arrive at grammatically correct and more idiomatic simplifications, future research could study the integration of association measures based on co-occurrence data.

## introduction the rise of digital corpora has been steadily transforming the fl learning domain. as corpora are an easy-to-compile source of natural text which can be consulted in a highly efficient fashion @xcite , they are arriving at a stage of being seamlessly embedded in several aspects of the everyday language learning practice @xcite . this "normalisation" @xcite of corpora is especially evidenced in the growing interest in data-driven learning (ddl; @xcite . in its broadest sense, this area refers to both teachers and learners "using the tools and techniques of corpus linguistics for pedagogical purposes" @xcite . while learner-led ddl activities tend to consist in analysing concordance lines (e.g. to discover collocations), teacherfocused ddl usually corresponds to accessing corpora directly in order to generate resources such as vocabulary lists and fill-the-gap exercises, which has led to the concept of "corpus-informed language teaching" (jablonkai and csomay, 2022). however, working with corpora also entails challenges and limitations, for instance with regard to learner proficiency levels. to begin with, ddl has been found to be beneficial for intermediate and advanced learners @xcite , but with lower levels the credentials of using corpora still have to be established @xcite . furthermore, also between intermediate and advanced learners considerable differences can exist, for example with respect to vocabulary knowledge: the lower one's language proficiency, the less extensive one's vocabulary will be @xcite . in ddl, this can lead to the following scenario: while preparing a language for specific purposes (lsp) class on economics, an sfl teacher is using a corpus query tool to create a fill-the-gap exercise for the target item arancel and finds sentence (a) below in the query output. however, if this sentence were to be included in the final exercise, low-or intermediateproficiency learners could find themselves unable to solve it, as their limited vocabulary knowledge might prevent them from understanding essential parts of the context, such as the word esquivar. to overcome this limitation, (part of) the corpus data can be simplified according to the needs of the target audience @xcite . as manual simplification constitutes a timeconsuming task, automating the simplification procedure could provide a more viable solution, especially when large corpora are involved. this study aims to contribute to this barely explored area of automatic ts for fl learning purposes (section 2.1). we specifically focus on the natural language processing (nlp) technique of lexical simplification (section 2.2), which will be used to adapt ddl activities to the needs of dutchspeaking b2-level sfl learners. apart from presenting this novel ls method (section 3), the study also introduces a new type of human-based evaluation, distinguished by its particular pedagogical focus (section 4). ## discussion and conclusion in this study, we presented a spanish ls method tailored to fl learning as the target setting. by simplifying all potentially complex words except the vocabulary item to be studied, the method adapts ddl activities to a given proficiency level while also taking into account the language acquisition theory of providing comprehensible input which is just somewhat beyond the current knowledge of the target audience @xcite . as we specifically focused on sfl learners with dutch as their mother tongue, the findings of this study primarily contribute to ls for this particular language combination. however, if equivalent resources (graded vocabulary learning resources, language models, etc.) are available, the methodological design of the ls pipeline can be applied to any language. to analyse performance, a new type of humanbased evaluation was carried out, which revealed the potential of the system (43% of the top-ranked predictions being found suitable) and suggested that meaning preservation is an important though not always necessary condition for obtaining both successfully simplified and pedagogically suitable example sentences. however, the results also showed that the custom-made cwi classifier leaves room for improvement, that many simplifications lack idiomaticity and that the substitution selection component is not yet able to exclude all non-grammatical replacements. to overcome these limitations in the future, we first of all aim to further develop the cwi classifier and evaluate it in a separate experiment. next, to arrive at grammatically correct and more idiomatic substitution candidates, we also plan to implement "typicality"-related measures (e.g. association measures based on co-occurrence data; gries, 2013) into the substitution selection and ranking components. finally, we will study the addition of weights to the ranking calculation, in order to balance the relative importance of the criteria. as a final observation, it should be highlighted that the teacher-focused ddl perspective adopted in this study also comes with its limitations. the expert knowledge of teachers and the contents of scientifically grounded vocabulary learning resources (as the ones used in this study to train the cwi classifier) can be valuable indicators of lexical complexity, but they often exhibit a lack of systematicity and do not capture how fl learners perceive lexical complexity themselves @xcite . therefore, in future research we will also collect "non-native data" and integrate them into the ls methodology. the pedagogically oriented evaluation, for instance, could be performed by sfl learners in the form of a bestworst scaling experiment in which learners have to indicate the best and worst item in a set of four versions of the same sentence (the original sentence plus three sentences with the complex word being replaced by the three top-ranked substitution candidates). criterion values applied search term number of @xmath0: sentence has to contain a finite verb, a subject and a verbal root incompleteness sentence has to start with a capital letter and end with a punctuation mark non-lemmatised @xmath1, not an implicit subject integrated into the verb form context independence structural connective in isolation not allowed: sentence cannot contain connectives in sentence-initial position unless it consists of more than one clause pronominal anaphora not allowed: sentence cannot contain tokens which have been assigned the "dm" tag or which have eso, esto, aquello or tal as their lemma adverbial anaphora not allowed: sentence cannot contain time or location adverbs which behave anaphorically, such as entonces ('then') l2 complexity l2 complexity in cefr level this criterion is excluded, as complex words are supposed to be identified in the cwi step and replaced by simpler alternatives additional structural criteria negative formulations not allowed: sentence cannot contain tokens which have been assigned the "ccneg" or "neg" tag interrogative sentence not allowed: sentence cannot contain question marks direct speech allowed answer to closed questions not allowed: sentence cannot start with adverbs or interjections such as sí ('yes') or no ('no') preceded and followed by delimiters such as commas modal verbs allowed sentence @xmath2, as complex words are supposed to be identified in the cwi step and replaced by simpler alternatives word frequency no limitations sensitive vocabulary not allowed: sentence cannot contain tokens which appear in a self-compiled list of swear words typicality no limitations proper names not allowed: sentence cannot contain tokens which have been assigned the "xp" tag