Speech acquisition

Speech acquisition focuses on the development of spoken language by a child. Speech consists of an organized set of sounds or phonemes that are used to convey meaning while language is an arbitrary association of symbols used according to prescribed rules to convey meaning. While grammatical and syntactic learning can be seen as a part of language acquisition, speech acquisition focuses on the development of speech perception and speech production over the first years of a child's lifetime. There are several models to explain the norms of speech sound or phoneme acquisition in children.

Sensory learning concerning acoustic speech signals already starts during pregnancy. Hepper and Shahidullah (1992) described the progression of fetal response to different pure tone frequencies. They suggested fetuses respond to 500 Hertz (Hz) ar 19 weeks gestation, 250 Hz and 500 Hz at 27 weeks gestation and finally respond to 250, 500, 1000, 3000 hz between 33 and 35 weeks gestation. Lanky and Williams (2005) suggested that fetuses could respond to pure tone stimuli of 500 hz as early as 16 weeks.

The newborn is already capable of discerning many phonetic contrasts. This capability may be innate. Speech perception becomes language-specific for vowels at around 6 months, for sound combinations at around 9 months and for language-specific consonants at around 11 months.

It is also important that a newborn is already capable of detecting typical word stress patterns around the age of 8 months.

As an infant grows into a child their ability to discriminate between speech sounds should increase. Rvachew (2007) described three developmental stages in which a child recognizes or discerns adult-like, phonological and articulatory representations of sounds.In the first stage, the child is generally unaware of phonological contrast and can produce sounds that are acoustically and perceptually similar. In the second stage the child is aware of phonological contrasts and can produce acoustically different variations imperceptible to adult listeners. Finally, in the third stage, children become aware of phonological contrasts and produce different sounds that are perceptually and acoustically accurate to an adult production.

It is suggested that a child's perceptual capabilities continue to develop for many years. Hazan and Barrett (2000) suggest that this development can cotton into late childhood; 6 to 12 year old children showed increasing mastery of discriminating synthesized differences in place, manner, and voicing of speech sounds with out yet achieving adult-like accuracy in their own production.

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