The Articulatory Basis of Positional Asymmetries in Phonological Acquisition by Tara K. McAllister A.B./A.M. in Linguistics Harvard University 2003 M.S. in Speech-Language Pathology Boston University 2007 Submitted to the Department of Linguistics and Philosophy in partial fulfillment of the requirements of the degree of Doctor of Philosophy in Linguistics at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY May 2009 © 2009 Tara McAllister. All rights reserved. The author hereby grants to MIT permission to reproduce and to distribute publicly paper and electronic copies of this thesis document in whole or in part in any medium now known or hereafter created. Signature of Author: ____________________________________________________________ Department of Linguistics and Philosophy May 29, 2009 Certified by: ___________________________________________________________________ Adam Albright Associate Professor of Linguistics Thesis Supervisor Accepted by: __________________________________________________________________ Irene Heim Professor of Linguistics Department Head The Articulatory Basis of Positional Asymmetries in Phonological Acquisition by Tara K. McAllister Submitted to the Department of Linguistics and Philosophy on May 29th, 2009 in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Linguistics ABSTRACT Child phonological processes that lack counterparts in adult phonological typology have long posed a problem for formal modeling of phonological acquisition. This dissertation investigates child-specific processes with a focus on the phenomenon of neutralization in strong position, whereby children preferentially neutralize phonemic contrast in precisely those contexts seen to support maximal contrast in adult systems. These processes are difficult to model without making incorrect predictions for adult typology. Here, it is argued that all genuinely child- specific processes are driven by constraints rooted in child-specific phonetic factors. In a phonetically-based approach to phonology, if there are areas of divergence in phonetic pressures across immature and mature systems, differences across child and adult phonologies are predicted rather than problematic. The phonetically-based approach also explains the developmental elimination of child-specific processes, since in the course of typical maturation, the phonetic pressures driving these effects will cease to apply. Because children‘s speech-motor control capabilities are known to diverge from those of the skilled adult speaker, it is posited that articulatory factors play the dominant role in shaping child-specific phonological processes. Here it is argued that children have difficulty executing discrete movements of individual articulators, notably the tongue. By moving the tongue-jaw complex as a single unit, the child speaker can reduce the number of degrees of movement freedom and also rely on the action of the motorically simpler mandible to achieve articulatory targets. The effects of mandibular dominance have previously been argued to play a role in shaping sound patterns in babbling and early words (MacNeilage & Davis, 1990). The preference for jaw-dominated movement can be seen to recede over time as the child establishes more reliable articulatory control. However, here evidence from the productions of older children is presented indicating that these effects continue to have an influence in later stages of development than has been previously documented. The pressure to use simultaneous movements of the tongue-jaw complex, formalized in a constraint MOVE-AS-UNIT, is argued to play a role in shaping child-specific processes including positional velar fronting, prevocalic fricative gliding, and consonant harmony. In the present approach, children‘s tendency to neutralize contrast in strong positions arises as MOVE-AS-UNIT interacts with asymmetries in the force and duration of articulatory gestures across different prosodic contexts. The incorporation of child-specific phonetic factors makes it possible to account for complex patterns of conditioning in child speech processes that would under other assumptions be extremely challenging to model. Thesis Supervisor: Adam Albright Title: Associate Professor of Linguistics 2 Table of Contents Chapter 1. The problem of child-specific phonological processes .......................................... 10 1. Positional neutralization in child and adult phonological processes ..................................... 10 1.1 Strong and weak contexts in adult phonological processes ............................................. 11 1.2 Positional processes in child phonology .......................................................................... 12 2. Phonological models of positional neutralization ................................................................. 13 2.1 Positional faithfulness...................................................................................................... 14 2.2 Positional markedness ..................................................................................................... 15 2.3 Positional neutralization and perceptual prominence ...................................................... 16 3. Child-specific processes as a reflection of articulatory differences ...................................... 18 4. On the incorporation of phonetic factors into phonology ..................................................... 20 4.1 Phonetic influence through diachronic changes .............................................................. 21 4.2 Phonetically governed constraint selection ..................................................................... 22 4.3 Direct incorporation of phonetic factors .......................................................................... 23 4.4 Modeling child-specific processes with directly phonetic constraints ............................ 25 5. Conclusion ............................................................................................................................. 25 Chapter 2. Articulatory maturation and implications for child phonology .......................... 27 1. Child phonological processes as child-specific articulatory limitations ............................... 27 2. General principles of speech-motor maturation .................................................................... 27 2.1 Consistency versus variability in speech production ...................................................... 28 2.2 Inter-articulator and inter-system coordination .............................................................. 28 2.3 Rate of speech and gestural duration .............................................................................. 28 2.4 Rhythm of speech production ......................................................................................... 29 3. Skilled versus unskilled motor action .................................................................................. 29 3.1 The stability-efficiency tradeoff in early motor development ........................................ 29 3.2 Mandibular dominance in early speech-motor control ................................................... 30 3.3 The ballistic-controlled distinction ................................................................................. 31 3.4 Undifferentiated lingual gestures .................................................................................... 32 4. Phonological consequences of mandibular dominance ......................................................... 33 4.1 On the phonological status of mandibular dominance effects ......................................... 34 4.2 Assessing violations of MOVE-AS-UNIT .......................................................................... 35 3 4.3 Phonological manifestations of MOVE-AS-UNIT............................................................. 36 4.4 The maturational elimination of mandibular dominance ............................................... 39 5. Perceptual consequences of child articulatory limitations .................................................... 40 6. Childhood apraxia of speech ................................................................................................. 42 6.1 Characterization of childhood apraxia of speech ........................................................... 42 6.2 Relevance of apraxia of speech for general phonological development ........................ 44 6.3 Case study subject .......................................................................................................... 45 7. Conclusion ............................................................................................................................ 46 Chapter 3. Relating error patterns in perception and production ......................................... 48 1. Overview ............................................................................................................................... 48 2. A perceptual account of neutralization in strong position..................................................... 49 3. Experimental Investigation of Perception and Production .................................................... 52 3.1 Purpose of experiment ..................................................................................................... 52 3.2 Methods ........................................................................................................................... 52 3.3 Experimental design .......................................................................................................