Linguistics

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Subject: search.filters.subject.Language, Linguistics

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    A Formal Model of Ambiguity and its Applications in Machine Translation
    (2010) Dyer, Christopher; Resnik, Philip; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Systems that process natural language must cope with and resolve ambiguity. In this dissertation, a model of language processing is advocated in which multiple inputs and multiple analyses of inputs are considered concurrently and a single analysis is only a last resort. Compared to conventional models, this approach can be understood as replacing single-element inputs and outputs with weighted sets of inputs and outputs. Although processing components must deal with sets (rather than individual elements), constraints are imposed on the elements of these sets, and the representations from existing models may be reused. However, to deal efficiently with large (or infinite) sets, compact representations of sets that share structure between elements, such as weighted finite-state transducers and synchronous context-free grammars, are necessary. These representations and algorithms for manipulating them are discussed in depth in depth. To establish the effectiveness and tractability of the proposed processing model, it is applied to several problems in machine translation. Starting with spoken language translation, it is shown that translating a set of transcription hypotheses yields better translations compared to a baseline in which a single (1-best) transcription hypothesis is selected and then translated, independent of the translation model formalism used. More subtle forms of ambiguity that arise even in text-only translation (such as decisions conventionally made during system development about how to preprocess text) are then discussed, and it is shown that the ambiguity-preserving paradigm can be employed in these cases as well, again leading to improved translation quality. A model for supervised learning that learns from training data where sets (rather than single elements) of correct labels are provided for each training instance and use it to learn a model of compound word segmentation is also introduced, which is used as a preprocessing step in machine translation.
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    COMMITMENT AND FLEXIBILITY IN THE DEVELOPING PARSER
    (2010) Omaki, Akira; Phillips, Colin; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation investigates adults and children's sentence processing mechanisms, with a special focus on how multiple levels of linguistic representation are incrementally computed in real time, and how this process affects the parser's ability to later revise its early commitments. Using cross-methodological and cross-linguistic investigations of long-distance dependency processing, this dissertation demonstrates how paying explicit attention to the procedures by which linguistic representations are computed is vital to understanding both adults' real time linguistic computation and children's reanalysis mechanisms. The first part of the dissertation uses time course evidence from self-paced reading and eye tracking studies (reading and visual world) to show that long-distance dependency processing can be decomposed into a sequence of syntactic and interpretive processes. First, the reading experiments provide evidence that suggests that filler-gap dependencies are constructed before verb information is accessed. Second, visual world experiments show that, in the absence of information that would allow hearers to predict verb content in advance, interpretive processes in filler-gap dependency computation take around 600ms. These results argue for a predictive model of sentence interpretation in which syntactic representations are computed in advance of interpretive processes. The second part of the dissertation capitalizes on this procedural account of filler-gap dependency processing, and reports cross-linguistic studies on children's long-distance dependency processing. Interpretation data from English and Japanese demonstrate that children actively associate a fronted wh-phrase with the first VP in the sentence, and successfully retract such active syntactic commitments when the lack of felicitous interpretation is signaled by verb information, but not when it is signaled by syntactic information. A comparison of the process of anaphor reconstruction in adults and children further suggests that verb-based thematic information is an effective revision cue for children. Finally, distributional analyses of wh-dependencies in child-directed speech are conducted to investigate how parsing constraints impact language acquisition. It is shown that the actual properties of the child parser can skew the input distribution, such that the effective distribution differs drastically from the input distribution seen from a researcher's perspective. This suggests that properties of developing perceptual mechanisms deserve more attention in language acquisition research.
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    Relating Movement and Adjunction in Syntax and Semantics
    (2010) Hunter, Timothy; Weinberg, Amy; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    In this thesis I explore the syntactic and semantic properties of movement and adjunction in natural language, and suggest that these two phenomena are related in a novel way. In a precise sense, the basic pieces of grammatical machinery that give rise to movement, also give rise to adjunction. In the system I propose, there is no atomic movement operation and no atomic adjunction operation; the terms "movement" and "adjunction" serve only as convenient labels for certain combinations of other, primitive operations. As a result the system makes non-trivial predictions about how movement and adjunction should interact, since we do not have the freedom to stipulate arbitrary properties of movement while leaving the properties of adjunction unchanged, or vice-versa. I focus first on the distinction between arguments and adjuncts, and propose that the differences between these two kinds of syntactic attachment can be thought of as a transparent reflection of the differing ways in which they contribute to neo-Davidsonian logical forms. The details of this proposal rely crucially on a distinctive treatment of movement, and from it I derive accurate predictions concerning the equivocal status of adjuncts as optionally included in or excluded from a maximal projection, and the possibility of counter-cyclic adjunction. The treatment of movement and adjunction as interrelated phenomena furthermore enables us to introduce a single constraint that subsumes two conditions on extraction, namely adjunct island effects and freezing effects. The novel conceptions of movement and semantic composition that underlie these results raise questions about the system's ability to handle semantic variable-binding. I give an unconventional but descriptively adequate account of basic quantificational phenomena, to demonstrate that this important empirical ground is not given up. More generally, this thesis constitutes a case study in (i) deriving explanations for syntactic patterns from a restrictive, independently motivated theory of compositional semantics, and (ii) using a computationally explicit framework to rigourously investigate the primitives and consequences of our theories. The emerging picture that is suggested is one where some central facts about the syntax and semantics of natural language hang together in a way that they otherwise would not.
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    The importance of being a complement: CED effects revisited
    (2010) Jurka, Johannes; Hornstein, Norbert R; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation revisits subject island effects (Ross 1967, Chomsky 1973) cross-linguistically. Controlled acceptability judgment studies in German, English, Japanese and Serbian suggest that extraction out of specifiers is consistently degraded compared to extraction out of complements, indicating that the Condition on Extraction domains (CED, Huang 1982) is still empirically viable, contrary to recent claims (Stepanov 2007). As a consequence, recent treatments of the CED in terms of Multiple Spell-Out (Uriagereka 1999) are still tenable. First, a series of NP-subextraction experiments in German using was für-split is discussed. The results indicate that subject island effects cannot be reduced to freezing effects (Wexler \& Culicover 1981). Extraction out of in-situ subjects is degraded compared to extraction out of in-situ objects. Freezing incurs an additional cost, i.e., extraction out of moved domains is degraded compared to in-situ domains. Further results from German indicate that extraction out of in-situ unaccusative and passive subjects is en par with extraction out of objects, while extraction out of in-situ transitive and intransitive unergative subjects causes a decrease in acceptability. Additionally, extraction out of indirect objects is degraded compared to extraction out of direct objects. It is also observed that a second gap improves the acceptability of otherwise illicit was für-split, a phenomenon dubbed Across-the-Board (ATB)-was für-splitand analysed in terms of Sideward Movement (Hornstein \& Nunes 2002). Furthermore, wh-extraction out of non-finite sentential arguments also shows a significant subject/object asymmetry. Experiments in English indicate that NP-subextraction yields the familiar subject/object asymmetry, while the contrast largely disappears when PPs are fronted. Further results show that ECM and passive predicates do not improve the acceptability of the extraction out of subjects. Finally, subject subextraction patterns in Japanese and Serbian are investigated. Both Long-distance scrambling and clefting out of sentential subjects in Japanese leads to a stronger degradation than out of sentential objects. PP-extraction in Serbian also shows the same subject/object asymmetry, while no such contrast is found for Left Branch Extraction.
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    COMPUTATIONAL ANALYSIS OF THE CONVERSATIONAL DYNAMICS OF THE UNITED STATES SUPREME COURT
    (2009) Hawes, Timothy; Lin, Jimmy; Resnik, Philip; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The decisions of the United States Supreme Court have far-reaching implications in American life. Using transcripts of Supreme Court oral arguments this work looks at the conversational dynamics of Supreme Court justices and links their conversational interaction with the decisions of the Court and individual justices. While several studies have looked at the relationship between oral arguments and case variables, to our knowledge, none have looked at the relationship between conversational dynamics and case outcomes. Working from this view, we show that the conversation of Supreme Court justices is both predictable and predictive. We aim to show that conversation during Supreme Court cases is patterned, this patterned conversation is associated with case outcomes, and that this association can be used to make predictions about case outcomes. We present three sets of experiments to accomplish this. The first examines the order of speakers during oral arguments as a patterned sequence, showing that cohesive elements in the discourse, along with references to individuals, provide significant improvements over our "bag-of-words" baseline in identifying speakers in sequence within a transcript. The second graphically examines the association between speaker turn-taking and case outcomes. The results presented with this experiment point to interesting and complex relationships between conversational interaction and case variables, such as justices' votes. The third experiment shows that this relationship can be used in the prediction of case outcomes with accuracy ranging from 62.5% to 76.8% for varying conditions. Finally, we offer recommendations for improved tools for legal researchers interested in the relationship between conversation during oral arguments and case outcomes, and suggestions for how these tools may be applied to more general problems.
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    Fine-Grained Linguistic Soft Constraints on Statistical Natural Language Processing Models
    (2009) Marton, Yuval Yehezkel; Resnik, Philip; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation focuses on effective combination of data-driven natural language processing (NLP) approaches with linguistic knowledge sources that are based on manual text annotation or word grouping according to semantic commonalities. I gainfully apply fine-grained linguistic soft constraints -- of syntactic or semantic nature -- on statistical NLP models, evaluated in end-to-end state-of-the-art statistical machine translation (SMT) systems. The introduction of semantic soft constraints involves intrinsic evaluation on word-pair similarity ranking tasks, extension from words to phrases, application in a novel distributional paraphrase generation technique, and an introduction of a generalized framework of which these soft semantic and syntactic constraints can be viewed as instances, and in which they can be potentially combined. Fine granularity is key in the successful combination of these soft constraints, in many cases. I show how to softly constrain SMT models by adding fine-grained weighted features, each preferring translation of only a specific syntactic constituent. Previous attempts using coarse-grained features yielded negative results. I also show how to softly constrain corpus-based semantic models of words (“distributional profiles”) to effectively create word-sense-aware models, by using semantic word grouping information found in a manually compiled thesaurus. Previous attempts, using hard constraints and resulting in aggregated, coarse-grained models, yielded lower gains. A novel paraphrase generation technique incorporating these soft semantic constraints is then also evaluated in a SMT system. This paraphrasing technique is based on the Distributional Hypothesis. The main advantage of this novel technique over current “pivoting” techniques for paraphrasing is the independence from parallel texts, which are a limited resource. The evaluation is done by augmenting translation models with paraphrase-based translation rules, where fine-grained scoring of paraphrase-based rules yields significantly higher gains. The model augmentation includes a novel semantic reinforcement component: In many cases there are alternative paths of generating a paraphrase-based translation rule. Each of these paths reinforces a dedicated score for the “goodness” of the new translation rule. This augmented score is then used as a soft constraint, in a weighted log-linear feature, letting the translation model learn how much to “trust” the paraphrase-based translation rules. The work reported here is the first to use distributional semantic similarity measures to improve performance of an end-to-end phrase-based SMT system. The unified framework for statistical NLP models with soft linguistic constraints enables, in principle, the combination of both semantic and syntactic constraints -- and potentially other constraints, too -- in a single SMT model.
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    BEYOND STATISTICAL LEARNING IN THE ACQUISITION OF PHRASE STRUCTURE
    (2009) Takahashi, Eri; Lidz, Jeffrey; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The notion that children use statistical distributions present in the input to acquire various aspects of linguistic knowledge has received considerable recent attention. But the roles of learner's initial state have been largely ignored in those studies. What remains unclear is the nature of learner's contribution. At least two possibilities exist. One is that all that learners do is to collect and compile accurately predictive statistics from the data, and they do not have antecedently specified set of possible structures (Elman, et al. 1996; Tomasello 2000). On this view, outcome of the learning is solely based on the observed input distributions. A second possibility is that learners use statistics to identify particular abstract syntactic representations (Miller & Chomsky 1963; Pinker 1984; Yang 2006). On this view, children have predetermined linguistic knowledge on possible structures and the acquired representations have deductive consequences beyond what can be derived from the observed statistical distributions alone. This dissertation examines how the environment interacts with the structure of the learner, and proposes a linking between distributional approach and nativist approach to language acquisition. To investigate this more general question, we focus on how infants, adults and neural networks acquire the phrase structure of their target language. This dissertation presents seven experiments, which show that adults and infants can project their generalizations to novel structures, while the Simple Recurrent Network fails. Moreover, it will be shown that learners' generalizations go beyond the stimuli, but those generalizations are constrained in the same ways that natural languages are constrained. This is compatible with the view that statistical learning interacts with inherent representational system, but incompatible with the view that statistical learning is the sole mechanism by which the existence of phrase structure is discovered. This provides novel evidence that statistical learning interacts with innate constraints on possible representations, and that learners have a deductive power that goes beyond the input data. This suggests that statistical learning is used merely as a method for mapping the surface string to abstract representation, while innate knowledge specifies range of possible grammars and structures.
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    Dimensions of Ellipsis: Investigations in Turkish
    (2009) Ince, Atakan; Lasnik, Howard; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation examines the elliptical structures of (a) sluicing (John called someone, but I don't know who!), (b) fragment answers (A: Who did John call?, B: Mary!), (c) gapping (John is eating ice-cream, and Mary apple pie!), and (d) Right Node Raising (John cooked and Mary ate the apple pie!) in Turkish and gives a `PF-deletion'-based analysis of all these elliptical structures. As to sluicing and fragment answers, evidence in support of PF-deletion comes from P-(non-)stranding and Case Matching, respectively. Further, these elliptical structures are island-insensitive in Turkish. As to gapping, this study gives a `movement + deletion' analysis, in which remnants in the second conjunct raise to the left periphery of the second conjunct and the rest of the second conjunct is elided. One striking property of gapping in Turkish is that it is a root phenomenon; in other words, it cannot occur in complement clauses, for instance. As to Right Node Raising, again, a PF-deletion analysis is given: the identical element(s) in the first conjunct is/are elided under identity with (an) element(s) in the second conjunct. The striking property of RNR is that remnants in this elliptical structure may not be clause-mate, in contrast to other elliptical structures -where remnants can be non-clause-mate under very specific contexts. This, I suggest, is due to the fact that PF-deletion in RNR applies at a later derivational stage than in other elliptical structures. In this stage, a syntactic derivation consists of linearized (sub-)lexical forms, where there is no hierarchical representation. This also suggests that Markovian system exists in grammar. In brief, this thesis looks at different elliptical structures in Turkish, and gives arguments for PF-deletion for all these elliptical structures, which has interesting implications for the generative theory.
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    On The Way To Linguistic Representation: Neuromagnetic Evidence of Early Auditory Abstraction in the Perception of Speech and Pitch
    (2009) Monahan, Philip Joseph; Idsardi, William J; Poeppel, David E; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The goal of this dissertation is to show that even at the earliest (non-invasive) recordable stages of auditory cortical processing, we find evidence that cortex is calculating abstract representations from the acoustic signal. Looking across two distinct domains (inferential pitch perception and vowel normalization), I present evidence demonstrating that the M100, an automatic evoked neuromagnetic component that localizes to primary auditory cortex is sensitive to abstract computations. The M100 typically responds to physical properties of the stimulus in auditory and speech perception and integrates only over the first 25 to 40 ms of stimulus onset, providing a reliable dependent measure that allows us to tap into early stages of auditory cortical processing. In Chapter 2, I briefly present the episodicist position on speech perception and discuss research indicating that the strongest episodicist position is untenable. I then review findings from the mismatch negativity literature, where proposals have been made that the MMN allows access into linguistic representations supported by auditory cortex. Finally, I conclude the Chapter with a discussion of the previous findings on the M100/N1. In Chapter 3, I present neuromagnetic data showing that the re-sponse properties of the M100 are sensitive to the missing fundamental component using well-controlled stimuli. These findings suggest that listeners are reconstructing the inferred pitch by 100 ms after stimulus onset. In Chapter 4, I propose a novel formant ratio algorithm in which the third formant (F3) is the normalizing factor. The goal of formant ratio proposals is to provide an explicit algorithm that successfully "eliminates" speaker-dependent acoustic variation of auditory vowel tokens. Results from two MEG experiments suggest that auditory cortex is sensitive to formant ratios and that the perceptual system shows heightened sensitivity to tokens located in more densely populated regions of the vowel space. In Chapter 5, I report MEG results that suggest early auditory cortical processing is sensitive to violations of a phonological constraint on sound sequencing, suggesting that listeners make highly specific, knowledge-based predictions about rather abstract anticipated properties of the upcoming speech signal and violations of these predictions are evident in early cortical processing.
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    Island repair and non-repair by PF strategies
    (2009) Nakao, Chizuru; Hornstein, Norbert R; Lasnik, Howard; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    Since Ross (1967), it has been observed that there are configurations from which otherwise unbounded movement operations cannot occur, and they are called islands. Ellipsis and resumption are known to have a peculiar property to `repair' island violations. Each chapter of this thesis discusses a case of ellipsis/resumption to examine in what cases movement out of an island becomes licit by those strategies. Chapter 2 discusses the elliptical construction called sluicing, and argues for the PF-deletion analysis of sluicing (Merchant 2001, originated from Ross 1969). I will show that ECP violations made by adjunct sluicing cannot be repaired by sluicing, unlike island violations. I will thus argue that island violations are PF-violations while ECP violations are LF violations, and that PF-deletion ameliorates only PF-deletion. Chapter 3 examines properties of stripping and argues that stripping is derived by focus movement followed by PF-deletion. I try to attribute the lack of island repair under ellipsis in stripping to the fact that focus movement is not usually overt in English. Covert movement is derived by a weak feature (Chomsky 1995), but when a focused material is included in the PF-deletion site, it undergoes last resort PF-movement to satisfy the recoverability of deletion. I claim that this PF-movement is incompatible with island-repair, speculating that island violations are ameliorated at spell-out, and post-spell-out movement is `too late' to be repaired. Chapter 4 reviews properties of Japanese sluicing, and introduces Hiraiwa and Ishihara's (2002) analysis where Japanese sluicing is derived from what they call "no da" in-situ focus construction. Under this analysis, the sluiced wh-phrase undergoes focus movement, followed by clausal deletion. I adopt the analysis of stripping to Japanese sluicing, claiming that this is another instance of the last resort focus movement at PF, which cannot ameliorate island violations. Chapter 5 discusses properties of Left Node Raising (LNR) in Japanese. Based on the fact that simple LNR shows properties distinct from Null Object Construction (NOC), I claim that LNR involves ATB-movement rather than NOC. However, the second gap of LNR behaves like a pronoun only when included inside an island. I claim that this is an instance of null resumptive pronoun.