Constrained Emergence of Universals and Variation in Syllable Systems

A computational model of emergent syllable systems is developed based on a set of functional constraints on syllable systems and the assumption that language structure emerges through cumulative change over time. The constraints were derived from general communicative factors as well as from the phonetic principles of perceptual distinctiveness and articulatory ease. Through evolutionary optimization, the model generated mock vocabularies optimized for the given constraints. Several simulations were run to understand how these constraints might define the emergence of universals and variation in complex sound systems. The predictions were that (1) CV syllables would be highly frequent in all vocabularies evolved under the constraints; (2) syllables with consonant clusters, consonant codas and vowel onsets would occur much less frequently; (3) a relationship would exist between the number of syllable types in a vocabulary and the average word length in the vocabulary; (4) different syllable types would emerge according to, what we termed, an <EM iterative principle of syllable structure> and their frequency would be directly related to their complexity; and (5) categorical differences would emerge between vocabularies evolved under the same constraints. Simulation results confirmed these predictions and provided novel insights into why regularities and differences may occur across languages. Specifically, the model suggested that both language universals and variation are consistent with a set of functional constraints that are fixed relative to one another. Language universals reflect underlying constraints on the system and language variation represents the many different and equally-good solutions to the unique problem defined by these constraints

Investigating Metrical Context Effects on Anticipatory Coarticulation in Connected Speech Development

If rhythm acquisition is influenced by the development of articulatory timing, then metrical structure might be expected to condition this timing. This study tested this hypothesis by investigating anticipatory effects of an upcoming noun on the production of a preceding determiner, under the assumption that anticipatory coarticulation indexes chunking. Simple S-V-O sentences were elicited from 5-year-olds, 8-year-olds, and adults. The V was either monosyllabic packed or disyllabic patted. The O was a determiner phrase where nouns varied either in onset place-of-articulation (POA; tack vs. cat) or in their rhymes (tack vs. toot). Acoustic analyses of determiner schwa F1 and F2 showed no effect of verb on schwa coarticulation. Given other results, including an interaction between age group and POA, the findings suggest that the acquisition of articulatory timing is independent of metrical structure, even if this timing is related to speech rhythm acquisition

The Acquisition of Two Phonetic Cues to Word Boundaries

The study evaluated whether durational and allophonic cues to word boundaries are intrinsic to syllable production, and so acquired with syllable structure, or whether they are suprasyllabic, and so acquired in phrasal contexts. Twenty preschool children (aged 3 ; 6 and 4 ; 6) produced: (1) single words with simple and complex onsets (e.g. nail vs. snail ); and (2) two-word phrases with intervocalic consonant sequences and varying boundary locations (e.g. this nail vs. bitty snail ). Comparisons between child and adult control productions showed that the durational juncture cue was emergent in the four-year-olds\u27 productions of two-word phrases, but absent elsewhere. In contrast, the allophonic cue was evident even in the three-year-olds\u27 productions of single words. Perceptual judgments showed that age- and type-dependent acoustic differences translated into differences in listener behavior. The differential acquisition of the two juncture cues is discussed with reference to the acquisition of articulatory timing control

Abrupt and Gradual Sound Change in an Expanding Lexicon £

The sound structure of language changes over time, but the process of change is not well understood. Sound change appears to occur abruptly as well as gradually, but it is not clear why, and it is not clear how the different rates of change affect the sound structures that emerge. This paper advances two hypotheses to answer these questions: (1) The Rate Hypothesis suggests that change occurs abruptly or gradually depending on how much an existing system is destabilized by social and cultural forces. (2) The Variation Hypothesis suggests that a greater diversity of sound structures emerge from abrupt change than gradual change because selection occurs on larger amounts of variation in more destabilized systems. These two hypotheses were tested in a computational model of sound change. The simulation results confirmed the hypotheses, and further suggested that abrupt change initially results in functionally suboptimal structure, whereas gradual change preserves good functionality. Overall, the study explains different rates of change in terms of a single framework and resolves a paradox in historical linguistics in which abrupt and gradual change are seen as incompatible, yet both exist.

Measurement Properties of Mean Length of Utterance in School-Age Children

Purpose: Mean length of utterance (MLU) is one of the most widely reported measures of syntactic development in the developmental literature, but its responsiveness in young school-age children\u27s language has been questioned, and it has been shown to correlate with nonsyntactic measures. This study tested the extent to which MLU shows measurement properties of responsiveness and construct validity when applied to language elicited from elementary school children. Method: Thirty-two typically developing children in two age groups (5 and 8 years) provided four short language samples each. Language samples were elicited in a question–answer context and a narrative context. MLU was calculated with both morpheme and word counts. Other established measures of syntactic complexity (clausal density [CD], developmental level [D-Level], mean length of clause [MLC]) and lexical diversity (lexical density, moving-average type–token ratio, number of different words) were also calculated. Results: Linear mixed-effects analyses revealed that MLU varied systematically with discourse context and children\u27s age group. The syntactic measures, CD and MLC, were found to vary systematically with MLU. None of the lexical diversity measures varied systematically with MLU. Conclusion: Results suggest that MLU is a responsive and valid measure of children\u27s syntactic development across age and discourse context during the early school-age years