Alternation-Sensitive Phoneme Learning: Implications For Children\u27s Development And Language Change

This dissertation develops a cognitive model describing when children learn to group distinct sound segments (allophones) into abstract equivalence classes (phonemes). The allophones an individual acquires are arbitrary and determined by their particular input, yet are intricately involved in language cognition once learned. The proposed acquisition model characterises the role of surface segment alternations in children\u27s input by using the Tolerance Principle (Yang 2016) to evaluate the cognitive cost of possible phoneme inventory structures iteratively as a child’s vocabulary grows. This Alternation-sensitive Phoneme Learning model therefore traces the emergence of abstract representations from concrete speech stimuli, starting from a default representation where underlying contrasts simply mirror surface-segment contrasts (Invariant Transparency Hypothesis, Ringe & Eska 2013). A longitudinal corpus study of four children\u27s alveolar stop and flap productions establishes that English medial flap allophony follows a U-shaped acquisition course, which is characteristic of learning linguistic rules or generalisations. The Alternation-sensitive Phoneme Learning cognitive model is then validated by accurately predicting the timing of changes in each child\u27s productions, which signal allophone acquisition. A second case study models the historical process of secondary split in Menominee mid and high back vowels. Here, the acquisition model serves as an independently motivated quantitative test for the occurrence of phonemic split, providing an alternative to traditional reliance on linguists\u27 case-specific subjective judgements about when it might occur. A third case study examines the phonemic status of the velar nasal in German, showing how this acquisition model can discriminate between tolerable grammars and the subset of tolerable grammars that are learnable, with implications for the relationship between formal language description and psychological representation. This dissertation\u27s approach synthesises insights from computational modelling, naturalistic corpus data, historical linguistics, and experimental research on child language acquisition

Expanding lexicons by inducing paradigms and validating attested forms

International audienceOne of the bottlenecks in Natural Language Processing for a given language is creating a lexicon that covers the language. The morphological lexicon provides two important pieces of information for NLP applications: 1) the normalization of a word, its lemmatization, which allows the application to recognize two variants of the same word; and 2) the part-of-speech roles that the word can play, which allows the application to parse the text, creating relations between the words in a text. Many NLP applications, e.g. Information Retrieval, Classification, Terminology Extraction, etc., depend upon the normalization and parsing information found in lexicons. When words are not present in these lexicons, it is difficult to predict what their proper lemmatizations and parts-of-speech are. In this paper we present a technique for updating a lexicon given an unknown word via induction of paradigms from an existing, but incomplete, lexicon and validation of the paradigm using corpus evidence

Induction, Semantic Validation and Evaluation of a Derivational Morphology Lexicon for German

This thesis is about computational morphology for German derivation. Derivation is a word formation process that creates new words from existing ones, where the base and the derived word share the same stem. Mostly, derivation is conducted by means of relatively regular affixation rules, as in to bake - bakery. In German, derivation is highly productive, thus leading to a high language variability which can be employed to express similar facts in different ways, as derivationally related words are often also semantically related (or transparent). However, linguistic variance is a challenge for computational applications, particularly in semantic processing: It makes it more difficult to automatically grasp the meaning of texts and to match similar information onto each other. Thus, computational systems require linguistic knowledge. We develop methods to induce and represent derivational knowledge, and to apply it in language processing. The main outcome of our study is DErivBase, a German derivational lexicon. It groups derivationally related words (words that are derived from the same stem) into derivational families. To achieve high quality and high coverage, we induce DErivBase by combining rule-based and data-driven methods: We implement linguistic derivation rules to define derivational processes, and feed lemmas extracted from a German corpus into the rules to derive new lemmas. All words that are connected - directly or indirectly - by such rules are considered a derivational family. As mentioned above, a derivational relationship often implies semantic relationship, but this is not always the case. Semantic drifts can cause semantically unrelated (opaque) derivational relations, such as to depart - department. Capturing the difference between transparent and opaque relations is important from a linguistic as well as a practical point of view. Thus, we conduct a semantic refinement of DErivBase, i.e., we determine which lemma pairs are derivationally and semantically related, and which are not. We establish a second, semantically validated version of our lexicon, where families are sub-clustered according to semantic coherence, using supervised machine learning methods: We learn a binary classifier based on features that arise from structural information about the derivation rules, and from distributional information about the semantic relatedness of lemmas. Accordingly, the derivational families are subdivided into semantically coherent clusters. To demonstrate the utility of the two lexicon versions, we evaluate them on three extrinsic - and in the broadest sense, semantic - tasks. The underlying assumption for applying DErivBase to semantic tasks is that derivational relatedness is a reasonable approximation to semantic relatedness, since derivation is often semantically transparent. Our three experiments are the following: 1., we incorporate DErivBase into distributional semantic models to overcome sparsity problems and to improve the prediction quality of the underlying model. We test this method, which we call derivational smoothing, for semantic similarity prediction, and for synonym choice. 2., we employ DErivBase to model a psycholinguistic experiment that examines priming effects of transparent and opaque derivations to draw conclusions about the mental lexical representation in German. Derivational information is again incorporated into a distributional model, but this time, it introduces a kind of morphological generalisation. 3., in order to solve the task of Recognising Textual Entailment, we integrate DErivBase into a matching-based entailment system by means of a query expansion. Assuming that derivational relationships between two texts suggest them to be entailing rather than non-entailing, this expansion increases the chance of a lexical overlap, which should improve the system's entailment predictions. The incorporation of DErivBase indeed improves the performance of the underlying systems in each task, however, it is differently suitable in different settings. In experiment 1., the semantically validated lexicon yields improvements over the purely morphological lexicon, and the more coarse-grained similarity prediction profits more from DErivBase than the synonym choice. In experiment 2., purely morphological information clearly outperforms the other lexicon version, as the latter cannot model opaque derivations. On the entailment task in experiment 3., DErivBase has only minor impact, because textual entailment is hard to solve by addressing only one linguistic phenomenon. In sum, our findings show that the induction of a high-quality, high-coverage derivational lexicon is beneficial for very different applications in computational linguistics. It might be worthwhile to further investigate the semantic aspects of derivation to better understand its impact on language and thus, on language processing

Information-theoretic causal inference of lexical flow

This volume seeks to infer large phylogenetic networks from phonetically encoded lexical data and contribute in this way to the historical study of language varieties. The technical step that enables progress in this case is the use of causal inference algorithms. Sample sets of words from language varieties are preprocessed into automatically inferred cognate sets, and then modeled as information-theoretic variables based on an intuitive measure of cognate overlap. Causal inference is then applied to these variables in order to determine the existence and direction of influence among the varieties. The directed arcs in the resulting graph structures can be interpreted as reflecting the existence and directionality of lexical flow, a unified model which subsumes inheritance and borrowing as the two main ways of transmission that shape the basic lexicon of languages. A flow-based separation criterion and domain-specific directionality detection criteria are developed to make existing causal inference algorithms more robust against imperfect cognacy data, giving rise to two new algorithms. The Phylogenetic Lexical Flow Inference (PLFI) algorithm requires lexical features of proto-languages to be reconstructed in advance, but yields fully general phylogenetic networks, whereas the more complex Contact Lexical Flow Inference (CLFI) algorithm treats proto-languages as hidden common causes, and only returns hypotheses of historical contact situations between attested languages. The algorithms are evaluated both against a large lexical database of Northern Eurasia spanning many language families, and against simulated data generated by a new model of language contact that builds on the opening and closing of directional contact channels as primary evolutionary events. The algorithms are found to infer the existence of contacts very reliably, whereas the inference of directionality remains difficult. This currently limits the new algorithms to a role as exploratory tools for quickly detecting salient patterns in large lexical datasets, but it should soon be possible for the framework to be enhanced e.g. by confidence values for each directionality decision

Information-theoretic causal inference of lexical flow

This volume seeks to infer large phylogenetic networks from phonetically encoded lexical data and contribute in this way to the historical study of language varieties. The technical step that enables progress in this case is the use of causal inference algorithms. Sample sets of words from language varieties are preprocessed into automatically inferred cognate sets, and then modeled as information-theoretic variables based on an intuitive measure of cognate overlap. Causal inference is then applied to these variables in order to determine the existence and direction of influence among the varieties. The directed arcs in the resulting graph structures can be interpreted as reflecting the existence and directionality of lexical flow, a unified model which subsumes inheritance and borrowing as the two main ways of transmission that shape the basic lexicon of languages

Proceedings of the Fifth Italian Conference on Computational Linguistics CLiC-it 2018 : 10-12 December 2018, Torino

On behalf of the Program Committee, a very warm welcome to the Fifth Italian Conference on Computational Linguistics (CLiC-­‐it 2018). This edition of the conference is held in Torino. The conference is locally organised by the University of Torino and hosted into its prestigious main lecture hall “Cavallerizza Reale”. The CLiC-­‐it conference series is an initiative of the Italian Association for Computational Linguistics (AILC) which, after five years of activity, has clearly established itself as the premier national forum for research and development in the fields of Computational Linguistics and Natural Language Processing, where leading researchers and practitioners from academia and industry meet to share their research results, experiences, and challenges

A distributional investigation of German verbs

Diese Dissertation bietet eine empirische Untersuchung deutscher Verben auf der Grundlage statistischer Beschreibungen, die aus einem großen deutschen Textkorpus gewonnen wurden. In einem kurzen Überblick über linguistische Theorien zur lexikalischen Semantik von Verben skizziere ich die Idee, dass die Verbbedeutung wesentlich von seiner Argumentstruktur (der Anzahl und Art der Argumente, die zusammen mit dem Verb auftreten) und seiner Aspektstruktur (Eigenschaften, die den zeitlichen Ablauf des vom Verb denotierten Ereignisses bestimmen) abhängt. Anschließend erstelle ich statistische Beschreibungen von Verben, die auf diesen beiden unterschiedlichen Bedeutungsfacetten basieren. Insbesondere untersuche ich verbale Subkategorisierung, Selektionspräferenzen und Aspekt. Alle diese Modellierungsstrategien werden anhand einer gemeinsamen Aufgabe, der Verbklassifikation, bewertet. Ich zeige, dass im Rahmen von maschinellem Lernen erworbene Merkmale, die verbale lexikalische Aspekte erfassen, für eine Anwendung von Vorteil sind, die Argumentstrukturen betrifft, nämlich semantische Rollenkennzeichnung. Darüber hinaus zeige ich, dass Merkmale, die die verbale Argumentstruktur erfassen, bei der Aufgabe, ein Verb nach seiner Aspektklasse zu klassifizieren, gut funktionieren. Diese Ergebnisse bestätigen, dass diese beiden Facetten der Verbbedeutung auf grundsätzliche Weise zusammenhängen.This dissertation provides an empirical investigation of German verbs conducted on the basis of statistical descriptions acquired from a large corpus of German text. In a brief overview of the linguistic theory pertaining to the lexical semantics of verbs, I outline the idea that verb meaning is composed of argument structure (the number and types of arguments that co-occur with a verb) and aspectual structure (properties describing the temporal progression of an event referenced by the verb). I then produce statistical descriptions of verbs according to these two distinct facets of meaning: In particular, I examine verbal subcategorisation, selectional preferences, and aspectual type. All three of these modelling strategies are evaluated on a common task, automatic verb classification. I demonstrate that automatically acquired features capturing verbal lexical aspect are beneficial for an application that concerns argument structure, namely semantic role labelling. Furthermore, I demonstrate that features capturing verbal argument structure perform well on the task of classifying a verb for its aspectual type. These findings suggest that these two facets of verb meaning are related in an underlying way