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Speech development is an aspect of psychomotor development and is the the increasing ability of children to control their vocal cords in order to speak clearly. It is different from language development.

Generally speech production is linked to perceptual development as the child has to discriminate between sounds i order to make progress.

Stages of pre-speech vocal development

Even though children do not produce their first words until they are approximately 12 months old, the ability to produce speech sounds starts to develop at a much younger age. Stark (1980) distinguishes five stages of early speech development:[1]

Infant vocalization

0-6 weeks: Reflexive vocalizations

These earliest vocalizations include crying and vegetative sounds such as breathing, sucking or sneezing. For these vegetative sounds, infants’ vocal cords vibrate and air passes through their vocal apparatus, thus familiarizing infants with processes involved in later speech production.

6-16 weeks: Cooing and laughter

Infants produce cooing sounds when they are content. Cooing is often triggered by social interaction with caregivers and resembles the production of vowels.

16-30 weeks: Vocal play

Infants produce a variety of vowel- and consonant-like sounds that they combine into increasingly longer sequences. The production of vowel sounds (already in the first 2 months) precedes the production of consonants, with the first back consonants (e.g., [g], [k]) being produced around 2-3 months, and front consonants (e.g., [m], [n], [p]) starting to appear around 6 months of age. As for pitch contours in early infant utterances, infants between 3 and 9 months of age produce primarily flat, falling and rising-falling contours. Rising pitch contours would require the infants to raise subglottal pressure during the vocalization or to increase vocal fold length or tension at the end of the vocalization, or both. At 3 to 9 months infants don’t seem to be able to control these movements yet.[2]

6-10 months: Reduplicated babbling (or canonical babbling[3])

Reduplicated babbling contains consonant-vowel (CV) syllables that are repeated in reduplicated series of the same consonant and vowel (e.g., [bababa]). At this stage, infants’ productions resemble speech much more closely in timing and vocal behaviors than at earlier stages. Starting around 6 months babies also show an influence of the ambient language in their babbling, i.e., babies’ babbling sounds different depending on which languages they hear. For example, French learning 9-10 month-olds have been found to produce a bigger proportion of prevoiced stops (which exist in French but not English) in their babbling than English learning infants of the same age.[4] This phenomenon of babbling being influenced by the language being acquired has been called babbling drift.[5]

10-14 months: Nonreduplicated babbling (or variegated babbling[6])

Infants now combine different vowels and consonants into syllable strings. At this stage, infants also produce various stress and intonation patterns. During this transitional period from babbling to the first word children also produce “protowords”, i.e., invented words that are used consistently to express specific meanings, but that are not real words in the children’s target language.[7] Around 12-14 months of age children produce their first word. Infants close to one year of age are able to produce rising pitch contours in addition to flat, falling, and rising-falling pitch contours.[8]

12-14 months

Infants usually produce their first word around 12 -14 months of age. First words are simple in structure and contain the same sounds that were used in late babbling.[9] The lexical items they produce are probably stored as whole words rather than as individual segments that get put together online when uttering them. This is suggested by the fact that infants at this age may produce the same sounds differently in different words.[10]

16 months

Children’s production vocabulary size at this age is typically around 50 words, although there is great variation in vocabulary size among children in the same age group, with a range between 0 and 160 words for the majority of children.[11]

18 months

Children’s productions become more consistent around the age of 18 months.[12] When their words differ from adult forms, these differences are more systematic than before. These systematic transformations are referred to as “phonological processes”, and often resemble processes that are typically common in the adult phonologies of the world’s languages (cf. reduplication in adult Jamaican Creole: “yellow yellow” = “very yellow” [13]). Some common phonological processes are listed below. [14]

Whole word processes (until age 3 or 4)

- Weak syllable deletion: omission of an unstressed syllable in the target word, e.g., [nænæ] for ‘banana’

- Final consonant deletion: omission of the final consonant in the target word, e.g., [pikʌ] for ‘because’

- Reduplication: production of two identical syllables based on one of the target word syllables, e.g., [baba] for ‘bottle’

- Consonant harmony: a target word consonant takes on features of another target word consonant, e.g., [gʌk] for ‘duck’

- Consonant cluster reduction: omission of a consonant in a target word cluster, e.g., [kæk] for ‘cracker’

Segment substitution processes (into the early school years)

- Velar fronting: a velar is replaced by a coronal sound, e.g., [ti] for ‘key’

- Stopping: a fricative is replaced by a stop, e.g., [ti] for ‘sea’

- Gliding: a liquid is replaced by a glide, e.g., [wæbɪt] for ‘rabbit’

2 years

The size of the production vocabulary ranges from about 50 to 550 words at the age of 2 years.[15] Influences on the rate of word learning, and thus on the wide range of vocabulary sizes of children of the same age, include the amount of speech children are exposed to by their caregivers as well as differences in how rich the vocabulary in the speech a child hears is. Children also seem to build up their vocabulary faster if the speech they hear is related to their focus of attention more often.[16][17] This would be the case if a caregiver talks about a ball the child is currently looking at.

4 years

A study by Gathercole and Baddeley (1989) showed the importance of sound for early word meaning.[18] They tested the phonological memory of 4- and 5-year-old children, i.e., how well these children were able to remember a sequence of unfamiliar sounds. They found that children with better phonological memory also had larger vocabularies at both ages. Moreover, phonological memory at age 4 predicted the children’s vocabulary at age 5, even with earlier vocabulary and nonverbal intelligence factored out.

7 years

Children produce mostly adult-like segments.[19] Their ability to produce complex sound sequences and multisyllabic words continues to improve throughout middle childhood.[20]


Biological foundations of infants’ speech development

The developmental changes in infants’ vocalizations over the first year of life are influenced by physical developments during that time. Physical growth of the vocal tract, brain development, and development of neurological structures responsible for vocalization are factors for the development of infants’ vocal productions.[21]

Infants’ vocal tract

Infants vocal tracts are smaller, and initially also shaped differently from adults’ vocal tracts. The infant’s tongue fills the entire mouth, thus reducing the range of movement. As the facial skeleton grows, the range for movement increases, which probably contributes to the increased variety of sounds infants start to produce. Development of muscles and sensory receptors also gives infants more control over sound production. [22] The limited movement possible by the infant jaw and mouth might be responsible for the typical consonant-vowel (CV) alternation in babbling and it has even been suggested that the predominance of CV syllables in the languages of the world might evolutionarily have been caused by this limited range of movements of the human vocal organs.[23]


The differences between the vocal tract of infants and adults can be seen in figure 3 (infants) and figure 4 (adults) below.

File:Infantvocaltract1.jpeg
File:Adultvocaltract.jpeg

The nervous system

Crying and vegetative sounds are controlled by the brain stem, which matures earlier than the cortex. Neurological development of higher brain structures coincides with certain developments in infants’ vocalizations. For example, the onset of cooing at 6 to 8 weeks happens as some areas of the limbic system begin to function. The limbic system is known to be involved in the expression of emotion, and cooing in infants is associated with a feeling of contentedness. Further development of the limbic system might be responsible for the onset of laughter around 16 weeks of age. The motor cortex, finally, which develops later than the abovementioned structures may be necessary for canonical babbling, which start around 6 to 9 months of age. [26].


See also

References

  1. Stark, R. E. (1980), "Stages of speech development in the first year of life", in Yeni-Komshian, G. H., Child Phonology. Volume 1: Production, New York, NY: Academic Press, pp. 73-92 
  2. Kent, R. D., A. D. Murray (1982). Acoustic features of infant vocalic utterances at 3, 6, and 9 months. Journal of the Acoustic Society of America 72: 353–363.
  3. Oller, D. K. (1986), "Metaphonology and infant vocalizations", in Lindblom, B., Precursors of Early Speech, New York, NY: Stockton Press, pp. 21-35 
  4. Whalen, D. H., A. G. Levitt, L. M. Goldstein (2007). VOT in the babbling of French- and English-learning infants. Journal of Phonetics 35: 341–352.
  5. Brown, R. (1958). How shall a thing be called?. Psychological Review 65: 14–21.
  6. Oller, D. K. (1986), "Metaphonology and infant vocalizations", in Lindblom, B., Precursors of Early Speech, New York, NY: Stockton Press, pp. 21-35 
  7. Bates, E. (1976). Language and Context: The Acquisition of Pragmatics, New York, NY: Academic Press.
  8. Kent, R. D., A. D. Murray (1982). Acoustic features of infant vocalic utterances at 3, 6, and 9 months. Journal of the Acoustic Society of America 72: 353–363.
  9. Vihman, M. M. (1996). Phonological Development. The Origins of Language in the Child, Oxford, UK: Blackwell.
  10. Walley, A. C. (1993). The role of vocabulary development in children's spoken word recognition and segmentation ability. Developmental Review 13: 286–350.
  11. Fenson, L.; P. S. Dale, J. S. Reznick, E. Bates, D. J. Thal, S. J. Pethick (1994), "Variability in early communicative development", Monographs of the Society for Research in Child Development 
  12. Vihman, M. M. (1996). Phonological Development. The Origins of Language in the Child, Oxford, UK: Blackwell.
  13. Gooden, S. (2003). The Phonology and Phonetics of Jamaican Creole Reduplication, Columbus, OH: The Ohio State University, PhD Dissertation.
  14. from Hoff, E. (2005). Language Development, Belmont, CA: Thomson Wadsworth.
  15. Fenson, L.; P. S. Dale, J. S. Reznick, E. Bates, D. J. Thal, S. J. Pethick (1994), "Variability in early communicative development", Monographs of the Society for Research in Child Development 
  16. Hoff, E., L. Naigles (2002). How children use input to acquire a lexicon. Child Development 73: 418–433.
  17. Hoff, E. (2005). Language Development, Belmont, CA: Thomson Wadsworth.
  18. Gathercole, S. E., A. D. Baddeley (1989). Evaluation of the role of phonological STM in the development of vocabulary in children: A longitudinal study. Journal of Memory and Language 28: 200–213.
  19. Sander, E. K. (1972). When are speech sounds learned?. Journal of Speech and Hearing Disorders 37: 55–63.
  20. Vihman, M. M. (1996). Phonological Development. The Origins of Language in the Child, Oxford, UK: Blackwell.
  21. Hoff, E. (2005). Language Development, Belmont, CA: Thomson Wadsworth.
  22. Hoff, E. (2005). Language Development, Belmont, CA: Thomson Wadsworth.
  23. MacNeilage, P. F., B. L. Davis (2001). Motor mechanisms in speech ontogeny: phylogenetic, neurobiological and linguistic implications. Current Opinion in Neurobiology 11: 696–700.
  24. Vihman, M. M. (1996). Phonological Development. The Origins of Language in the Child, Oxford, UK: Blackwell.
  25. Vihman, M. M. (1996). Phonological Development. The Origins of Language in the Child, Oxford, UK: Blackwell.
  26. Hoff, E. (2005). Language Development, Belmont, CA: Thomson Wadsworth.

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