Weighted Constraints in Generative Linguistics

Harmonic Grammar (HG) and Optimality Theory (OT) are closely related formal frameworks for the study of language. In both, the structure of a given language is determined by the relative strengths of a set of constraints. They differ in how these strengths are represented: as numerical weights (HG) or as ranks (OT). Weighted constraints have advantages for the construction of accounts of language learning and other cognitive processes, partly because they allow for the adaptation of connectionist and statistical models. HG has been little studied in generative linguistics, however, largely due to influential claims that weighted constraints make incorrect predictions about the typology of natural languages, predictions that are not shared by the more popular OT. This paper makes the case that HG is in fact a promising framework for typological research, and reviews and extends the existing arguments for weighted over ranked constraints

Extending adaptor grammars to learn phonological alternations

Recent advances in unsupervised learning of linguistic structure have demonstrated the feasibility of inferring latent morphological parses from an unannotated corpus given transparent underlying-to-surface mappings (ex., Adaptor Grammars), as well as in learning predictable phonological transformations from prespecified underlying morphemes to a range of surface allomorphs via a stochastic edit distance algorithm. In this paper we introduce a nonparametric Bayesian model which builds on the morpheme-segmentation success of AGs, and incorporates the ability to learn predictable phonological transformations of underlying forms to their surface allomorphs via the interaction of markedness and faithfulness principles, inspired by generative phonology. The unsupervised nature of this model (that is, no semantic information about the words being segmented is provided) is relevant not only computationally but also psychologically, as it mirrors developmental findings that young infants segment and cluster morphemes based solely on phonetic and distributional similarity. The model also incorporates many of the other cognitive restrictions infants during the initial period of morphophonological learning in an effort to make the model maximally realistic, and thus eventually useful in making quantitative predictions about the early stages of morphophonological acquisition that can be experimentally investigated. We evaluate the model on a novel dataset consisting of a complex system of allomorphy in Acehnese, an understudied Indonesian language

The Nature of Optional Sibilant Harmony in Navajo

This thesis represents investigates optional sibilant harmony in Navajo using the first person possessive morpheme, which contains an underlyingly palatal sibilant that may harmonize to alveolar when affixed to noun stems that contain [+anterior] sibilants. The literature commonly describes sibilant harmony as being mandatory in Navajo when sibilants are in adjacent syllables, and optional when there is more distance between sibilants. In other words, sibilant disharmony is ungrammatical, but gradiently rather than categorically; in some instances disharmony is ungrammatical enough that it must be repaired through assimilation, while in other instances it is less ungrammatical and may be tolerated. The statistical nature of the variation in these optional harmony settings is not fully understood, however, and the three studies contained within this thesis were designed to investigate how often assimilation occurs in nonmandatory environments and to identify factors that contribute to the variability observed. In the first study, a Google search was used to evaluate sibilant harmony in online Navajo language use in the Spring of 2008 and again in the Spring of 2010. The findings present a picture of optional sibilant harmony that differs somewhat from the traditional view; harmony seems to be optional even in the environment that has traditionally been described as mandatory, and it occurs far less frequently than anticipated. These results led to the creation of an online survey wherein fluent speakers of Navajo provided grammaticality judgments of both assimilated and unassimilated forms. Almost universally, respondents preferred the unassimilated shi- even in those environments where assimilation would previously have been considered mandatory. The third study involved the recording of data from three speakers of Navajo, none of whom use the assimilated si- either in writing or in speech--at least, not to a degree that is discernible to the naked ear. Acoustic analysis was performed to determine whether the prefix-initial palatal sibilant is acoustically consistent across the board--duration, spectral mean, onset of frication energy, and the second formant of the following vowel were measured to investigate whether the prefixal esh differs acoustically when it appears before words that contain potential triggers than when it does not. Analysis reveals some differences in the spectral mean and duration of the fricative portion of the first person possessive morpheme when it occurs before stems that contain [+anterior] sibilants. Taken together, the findings presented herein suggest that the mandatory sibilant harmony environment no longer exists in Navajo, at least with regards to the first person possessive morpheme. Harmony is far less prevalent than expected overall, and is wholly absent for some speakers. The factors of continuancy and adjacency were found to contribute significantly to the gradience observed in all three studies, however, even for those speakers who do not overtly use assimilation

How to meet the neighbors: Modality effects on phonological generalization

Long-term auditory priming of words from dense neighborhoods has been posited as a learning mechanism that affects change in the phonological structure of children’s lexical representations. An apparent confound associated with the modality of priming responsible for structural change has been introduced in the literature, which challenges this proposal. Thus, our purpose was to evaluate prime modality in treatment of children with phonological delay. Nine children were assigned to auditory-visual, auditory or visual priming of words from dense neighborhoods prior to treatment of production as the independent variable. The dependent variable was phonological generalization. Results showed that auditory priming (with or without visual input) promoted greater generalization on an order of magnitude of 3:1. Findings support the theoretical significance of auditory priming for phonological learning and demonstrate the applied utility of priming in clinical treatment.National Institutes of Health DC00433, RR7031K, DC00076, DC001694 (PI: Gierut

Statistical Knowledge and Learning in Phonology

This thesis deals with the theory of the phonetic component of grammar in a formal probabilistic inference framework: (1) it has been recognized since the beginning of generative phonology that some language-specific phonetic implementation is actually context-dependent, and thus it can be said that there are gradient "phonetic processes" in grammar in addition to categorical "phonological processes." However, no explicit theory has been developed to characterize these processes. Meanwhile, (2) it is understood that language acquisition and perception are both really informed guesswork: the result of both types of inference can be reasonably thought to be a less-than-perfect committment, with multiple candidate grammars or parses considered and each associated with some degree of credence. Previous research has used probability theory to formalize these inferences in implemented computational models, especially in phonetics and phonology. In this role, computational models serve to demonstrate the existence of working learning/per- ception/parsing systems assuming a faithful implementation of one particular theory of human language, and are not intended to adjudicate whether that theory is correct. The current thesis (1) develops a theory of the phonetic component of grammar and how it relates to the greater phonological system and (2) uses a formal Bayesian treatment of learning to evaluate this theory of the phonological architecture and for making predictions about how the resulting grammars will be organized. The coarse description of the consequence for linguistic theory is that the processes we think of as "allophonic" are actually language-specific, gradient phonetic processes, assigned to the phonetic component of grammar; strict allophones have no representation in the output of the categorical phonological grammar

Dense neighborhoods and mechanisms of learning: Evidence from children with phonological delay

There is a noted advantage of dense neighborhoods in language acquisition, but the learning mechanism that drives the effect is not well understood. Two hypotheses–long-term auditory word priming and phonological working memory–have been advanced in the literature as viable accounts. These were evaluated in two treatment studies enrolling 12 children with phonological delay. Study 1 exposed children to dense neighbors versus nonneighbors before training sound production in evaluation of the priming hypothesis. Study 2 exposed children to the same stimuli after training sound production as a test of the phonological working memory hypothesis. Results showed that neighbors led to greater phonological generalization than nonneighbors, but only when presented prior to training production. There was little generalization and no differential effect of exposure to neighbors or nonneighbors after training production. Priming was thus supported as a possible mechanism of learning behind the dense neighborhood advantage in phonological acquisition.National Institutes of Health DC00433, RR7031K, DC00076, DC001694 (PI: Gierut

Optimization models of natural communication

A family of information theoretic models of communication was introduced more than a decade ago to explain the origins of Zipf’s law for word frequencies. The family is a based on a combination of two information theoretic principles: maximization of mutual information between forms and meanings and minimization of form entropy. The family also sheds light on the origins of three other patterns: the principle of contrast; a related vocabulary learning bias; and the meaning-frequency law. Here two important components of the family, namely the information theoretic principles and the energy function that combines them linearly, are reviewed from the perspective of psycholinguistics, language learning, information theory and synergetic linguistics. The minimization of this linear function is linked to the problem of compression of standard information theory and might be tuned by self-organization.Peer ReviewedPostprint (author's final draft

Modeling Word Forms Using Latent Underlying Morphs and Phonology

The observed pronunciations or spellings of words are often explained as arising from the “underlying forms” of their mor- phemes. These forms are latent strings that linguists try to reconstruct by hand. We propose to reconstruct them automatically at scale, enabling generalization to new words. Given some surface word types of a concatenative language along with the abstract morpheme sequences that they ex- press, we show how to recover consistent underlying forms for these morphemes, together with the (stochastic) phonology that maps each concatenation of underly- ing forms to a surface form. Our technique involves loopy belief propagation in a nat- ural directed graphical model whose vari- ables are unknown strings and whose con- ditional distributions are encoded as finite- state machines with trainable weights. We define training and evaluation paradigms for the task of surface word prediction, and report results on subsets of 7 languages