Linguistics Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2787
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Item 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.Item 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.Item Lexical Structure and the Nature of Linguistic Representations(2006-08-09) Fiorentino, Robert D.; Poeppel, David; Linguistics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation addresses a foundational debate regarding the role of structure and abstraction in linguistic representation, focusing on representations at the lexical level. Under one set of views, positing abstract morphologically-structured representations, words are decomposable into morpheme-level basic units; however, alternative views now challenge the need for abstract structured representation in lexical representation, claiming non-morphological whole-word storage and processing either across-the-board or depending on factors like transparency/productivity/surface form. Our cross-method/cross-linguistic results regarding morphological-level decomposition argue for initial, automatic decomposition, regardless of factors like semantic transparency, surface formal overlap, word frequency, and productivity, contrary to alternative views of the lexicon positing non-decomposition for some or all complex words. Using simultaneous lexical decision and time-sensitive brain activity measurements from magnetoencephalography (MEG), we demonstrate effects of initial, automatic access to morphemic constituents of compounds, regardless of whole-word frequency, lexicalization and length, both in the psychophysical measure (response time) and in the MEG component indexing initial lexical activation (M350), which we also utilize to test distinctions in lexical representation among ambiguous words in a further experiment. Two masked priming studies further demonstrate automatic decomposition of compounds into morphemic constituents, showing equivalent facilitation regardless of semantic transparency. A fragment-priming study with spoken Japanese compounds argues that compounds indeed activate morphemic candidates, even when the surface form of a spoken compound fragment segmentally-mismatches its potential underlying morpheme completion due to a morpho-phonological alternation (rendaku), whereas simplex words do not facilitate segment-mismatching continuations, supporting morphological structure-based prediction regardless of surface-form overlap. A masked priming study on productive and non-productive Japanese de-adjectival nominal derivations shows priming of constituents regardless of productivity, and provides evidence that affixes have independent morphological-level representations. The results together argue that the morpheme, not the word, is the basic unit of lexical processing, supporting a view of lexical representations in which there are abstract morphemes, and revealing immediate, automatic decomposition regardless of semantic transparency, morphological productivity, and surface formal overlap, counter to views in which some/all complex words are treated as unanalyzed wholes. Instead, we conclude that morphologically-complex words are decomposed into abstract morphemic units immediately and automatically by rule, not by exception.