Linguistics Theses and Dissertations

Permanent URI for this collectionhttp://hdl.handle.net/1903/2787

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End date: 2009Subject: search.filters.subject.Psychology, Cognitive

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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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    The predictive nature of language comprehension
    (2009) Lau, Ellen Frances; Phillips, Colin; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation explores the hypothesis that predictive processing--the access and construction of internal representations in advance of the external input that supports them--plays a central role in language comprehension. Linguistic input is frequently noisy, variable, and rapid, but it is also subject to numerous constraints. Predictive processing could be a particularly useful approach in language comprehension, as predictions based on the constraints imposed by the prior context could allow computation to be speeded and noisy input to be disambiguated. Decades of previous research have demonstrated that the broader sentence context has an effect on how new input is processed, but less progress has been made in determining the mechanisms underlying such contextual effects. This dissertation is aimed at advancing this second goal, by using both behavioral and neurophysiological methods to motivate predictive or top-down interpretations of contextual effects and to test particular hypotheses about the nature of the predictive mechanisms in question. The first part of the dissertation focuses on the lexical-semantic predictions made possible by word and sentence contexts. MEG and fMRI experiments, in conjunction with a meta-analysis of the previous neuroimaging literature, support the claim that an ERP effect classically observed in response to contextual manipulations--the N400 effect--reflects facilitation in processing due to lexical-semantic predictions, and that these predictions are realized at least in part through top-down changes in activity in left posterior middle temporal cortex, the cortical region thought to represent lexical-semantic information in long-term memory,. The second part of the dissertation focuses on syntactic predictions. ERP and reaction time data suggest that the syntactic requirements of the prior context impacts processing of the current input very early, and that predicting the syntactic position in which the requirements can be fulfilled may allow the processor to avoid a retrieval mechanism that is prone to similarity-based interference errors. In sum, the results described here are consistent with the hypothesis that a significant amount of language comprehension takes place in advance of the external input, and suggest future avenues of investigation towards understanding the mechanisms that make this possible.
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    Form, meaning and context in lexical access: MEG and behavioral evidence
    (2009) Almeida, Diogo; Poeppel, David; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    One of the main challenges in the study of cognition is how to connect brain activity to cognitive processes. In the domain of language, this requires coordination between two different lines of research: theoretical models of linguistic knowledge and language processing on the one side and brain sciences on the other. The work reported in this dissertation attempts to link these two lines of research by focusing on one particular aspect of linguistic processing, namely lexical access. The rationale for this focus is that access to the lexicon is a mandatory step in any theory of linguistic computation, and therefore findings about lexical access procedures have consequences for language processing models in general. Moreover, in the domain of brain electrophysiology, past research on event-related brain potentials (ERPs) - electrophysiological responses taken to reflect processing of certain specific kinds of stimuli or specific cognitive processes - has uncovered different ERPs that have been connected to linguistic stimuli and processes. One particular ERP, peaking at around 400 ms post-stimulus onset (N400) has been linked to lexico-semantic processing, but its precise functional interpretation remains controversial: The N400 has been proposed to reflect lexical access procedures as well as higher order semantic/pragmatic processing. In a series of three MEG experiments, we show that access to the lexicon from print occurs much earlier than previously thought, at around 200 ms, but more research is needed before the same conclusion can be reached about lexical access based on auditory or sign language input. The cognitive activity indexed by the N400 and its MEG analogue is argued to constitute predictive processing that integrates information from linguistic and non-linguistic sources at a later, post-lexical stage.
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    The structure of memory meets memory for structure in linguistic cognition
    (2008-08-19) Wagers, Matthew; Phillips, Colin; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation is concerned with the problem of how structured linguistic representations interact with the architecture of human memory. Much recent work has attempted to unify real-time linguistic memory with a general content-addressable architecture (Lewis & Vasishth, 2005; McElree, 2006). Because grammatical principles and constraints are strongly relational in nature, and linguistic representation hierarchical, this kind of architecture is not well suited to restricting the search of memory to grammatically-licensed constituents alone. This dissertation investigates under what conditions real-time language comprehension is grammatically accurate. Two kinds of grammatical dependencies were examined in reading time and speeded grammaticality experiments: subject-verb agreement licensing in agreement attraction configurations ("The runners who the driver wave to ..."; Kimball & Aissen, 1971, Bock & Miller, 1991), and active completion of wh-dependencies. We develop a simple formal model of agreement attraction in an associative memory that makes accurate predictions across different structures. We conclude that dependencies that can only be licensed exclusively retrospectively, by searching the memory to generate candidate analyses, are the most prone to grammatical infidelity. The exception may be retrospective searches with especially strong contextual restrictions, as in reflexive anaphora. However dependencies that can be licensed principally by a prospective search, like wh-dependencies or backwards anaphora, are highly grammatically accurate.
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    Pre-verbal Structure Building in Romance Languages and Basque
    (2006-08-04) Pablos, Leticia; Phillips, Colin; Uriagereka, Juan; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    The main goal of the work in this dissertation is to investigate pre-verbal structure building effects in languages with different configurations such as Spanish, Galician and Basque, by means of using different pre-verbal cues in order to show that syntactic structure can be both interpreted and anticipated before the verbal head. I examine the syntax of Clitic-Left Dislocations (CLLDs) and other kinds of left-dislocations in Spanish and then analyze their processing. I concentrate on the use of clitic pronouns in Spanish and Galician in CLLD constructions that require the presence of the clitic pronoun to interpret the left-dislocated phrase and where I examine if this left-dislocation is interpreted at the clitic pronoun. Experimental results from three self-paced reading experiments provide evidence that the clitic in these constructions is required and used to interpret the thematic features of the topicalized NP before the verb. Thus, I demonstrate that clitic pronouns are used as pre-verbal cues in parsing and that the active search mechanism is also triggered in long-distance dependencies involving clitic pronouns. I conclude that the active search mechanism is a more general architectural mechanism of the parser that is triggered in all kinds of long-distance dependencies, regardless of whether the search is triggered by gaps or pronouns. In Basque, verbal auxiliaries overtly encode agreement information that reflects the number of arguments of the verbal head. In negatives, auxiliaries are obligatorily fronted and split from the verbal head with which they otherwise form a cluster. Thus, verbal auxiliaries in Basque are a pre-verbal morphological cue that can assist the parser in predicting structure. Specifically, I examine how predictions for the upcoming structure of the sentence are determined by agreement information on the number of arguments specified in the auxiliary and by the mismatch of this auxiliary with the case features of the NP that follows it. I provide results from a self-paced reading experiment to argue that the parser uses the information encoded in the auxiliaries and demonstrate that the mismatch of the auxiliary with the following NP can prevent the reader from following a garden-path analysis of the sentence.
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    The Acquisition and Processing of Backwards Anaphora
    (2005-08-02) Kazanina, Nina; Phillips, Colin; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)
    This dissertation investigates long-distance backwards pronominal dependencies (backwards anaphora or cataphora) and constraints on such dependencies from the viewpoint of language development and real-time language processing. Based on the findings from a comprehension experiment with Russian-speaking children and on real-time sentence processing data from English and Russian adults I argue for a position that distinguishes structural and non-structural constraints on backwards anaphora. I show that unlike their non-syntactic counterparts, structural constraints on coreference, in particular Principle C of the Binding Theory (Chomsky 1981), are active at the earliest stage of language development and of real-time processing. In language acquisition, the results of a truth-value judgment task with 3-6 year old Russian-speaking children reveal a striking developmental asymmetry between Principle C, a cross-linguistically consistent syntactic constraint on coreference, and a Russian-specific discourse constraint on coreference. Whereas Principle C is respected by children already at the age of three, the Russian-specific (discourse) constraint is not operative in child language until the age of five. These findings present a challenge for input-driven accounts of language acquisition and are most naturally explained in theories that admit the existence of innately specified principles that underlie linguistic representations. In real-time processing, the findings from a series of self-paced reading experiments on English and Russian show that in backwards anaphora contexts the parser initiates an active search for an antecedent for the pronoun which is limited to positions that are not subject to structural constraints on coreference, e.g. Principle C. This grammatically constrained active search mechanism associated observed in the processing of backwards anaphora is similar to the mechanism found in the processing of another type of a long-distance dependency, the wh-dependency. I suggest that the early application of structural constraints on long-distance dependencies is due to reasons of parsing efficiency rather than due to their architectural priority, as such constraints aid to restrict the search space of possible representations to be built by the parser. A computational parsing algorithm is developed that combines the constrained active search mechanism with a strict incremental left-to-right structure building procedure.