Age-related increases of speaking rate are not fully understood, but have been attributed to gains in biologic factors and learned skills that support speech production. This study investigated developmental changes in speaking rate and articulatory kinematics of participants aged 4 (N = 7), 7 (N = 10), 10 (N = 9), 13 (N = 7), 16 (N = 9) years and young adults (N = 11) in speaking tasks varying in task demands. Speaking rate increased with age, with decreases in pauses and articulator displacements but not increases in articulator movement speed. Movement speed did not appear to constrain the speaking. Rather, age-related increases in speaking rate are due to gains in cognitive and linguistic processing and speech motor control.

In early speech development, progressive gains in phonetic ability represent progress in multiple domains (e.g., sensory, perceptual, cognitive, linguistic, and neuromotor) all of which are ultimately conveyed through the speech motor system. Accordingly, the comprehensive understanding of speech development requires knowledge about age-related changes in speech motor performance and about the factors affecting those changes during the various phases of speech development. In this chapter, we consider why motor-based descriptions are essential for addressing long-standing practical and theoretical issues regarding early speech development. We also present a conceptual framework for studying early speech motor development, which guides our current line of research inquiry. The conceptual framework proposes that developmental stages in speech motor behavior are guided by production constraints and catalysts to speech motor performance: Production constraints are factors that limit speech production abilities in young children and catalysts are factors that engender change toward mature speech. Finally, we consider findings from our studies on early speech motor development that are motivated by the framework. 10.1. Introduction: the need for motor-based descriptions of speech development To even the most casual observer, it is obvious that infants are capable of producing only a small number of crude, uncoordinated articulatory gestures. Learning to produce speech poses a significant physical challenge to the young child. The motor skills required to produce speech are among the most sophisticated learned by humans. During speech, a large number of muscles are activated to move respiratory, phonatory, and articulatory structures. Because speech is produced very quickly (180 words/minute or 15 sounds/second), speech muscles must be activated rapidly and timed precisely with respect to speech goals. Very little is understood about how young children learn this remarkable ability. Over the past three decades, a significant amount of research has been directed towards identifying the order in which typically developing children acquire and subsequently master new speech sounds, syllable shapes, and sound combinations (

Although the development of spoken language is dependent on the emergence of cognitive, language, and speech motor skills, knowledge about how these domains interact during the early stages of communication development is currently limited. This exploratory investigation examines the strength of associations between longitudinal changes in articulatory kinematics and development of skills in multiple domains thought to support early communication development. Twentyfour children were investigated every 3 months between the ages of 9 and 21 months. Movements of the upper lip, lower lip, and jaw were transduced using a three-dimensional motion capture system to obtain age-related changes in movement speed and range of movement. Standardized measures of cognition and language from the Battelle Developmental Inventory, 2nd edition and the MacArthur-Bates Communicative Development Inventory were also collected. Significant associations were identified between orofacial kinematic and the standardized measures of language and cognitive skills, even when age served as covariate.These findings provide preliminary evidence of interactions between cognition, language, and speech motor skills during early communication development. Further work is needed to identify and quantify causal relations among these co-emerging skills.Learning outcomes: The reader will be able to: (1) describe how cognition, language, and speech motor control may interact during speech development, (2) describe the associations between speech kinematic characteristics and measures of cognition and language.

Purpose Although a growing body of literature has indentified the positive effects of visual speech on speech and language learning, oral movements of infant-directed speech (IDS) have rarely been studied. This investigation used 3-dimensional motion capture technology to describe how mothers modify their lip movements when talking to their infants. Method Lip movements were recorded from 25 mothers as they spoke to their infants and other adults. Lip shapes were analyzed for differences across speaking conditions. The maximum fundamental frequency, duration, acoustic intensity, and first and second formant frequency of each vowel also were measured. Results Lip movements were significantly larger during IDS than during adult-directed speech, although the exaggerations were vowel specific. All of the vowels produced during IDS were characterized by an elevated vocal pitch and a slowed speaking rate when compared with vowels produced during adult-directed speech. Conclusion The pattern of lip-shape exaggerations did not provide support for the hypothesis that mothers produce exemplar visual models of vowels during IDS. Future work is required to determine whether the observed increases in vertical lip aperture engender visual and acoustic enhancements that facilitate the early learning of speech.

Aims: The breath group can serve as a functional unit to define temporal and fundamental frequency (f₀) features in continuous speech. These features of the breath group are determined by the physiologic, linguistic, and cognitive demands of communication. Reading and spontaneous speech are two speaking tasks that vary in these demands and are commonly used to evaluate speech performance for research and clinical applications. The purpose of this study is to examine differences between reading and spontaneous speech in the temporal and f₀ aspects of their breath groups. Methods: Sixteen participants read two passages and answered six questions while wearing a circumferentially vented mask connected to a pneumotach. The aerodynamic signal was used to identify inspiratory locations. The audio signal was used to analyze task differences in breath group structure, including temporal and f₀ components. Results: The main findings were that spontaneous speech task exhibited significantly more grammatically inappropriate breath group locations and longer breath group duration than did the passage reading task. Conclusion: The task differences in the percentage of grammatically inadequate breath group locations and in breath group duration for healthy adult speakers partly explain the differences in cognitive-linguistic load between the passage reading and spontaneous speech.