Chapter 2 Literature review
2.2 Factors of phonological variability
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to emerge in infants’ production.
Allen and Hawkins (1978, 1980) proposed that young children acquiring English
tend to use the form of disyllabic trochaic feet. They observed that children often use augmented (CVC→CVCV) or truncated words. Furthermore, this early syllable
structure might be a universal tendency; that is, children all over the world acquire
languages with uniformity. Demuth and Johnson (2003) also found that children acquiring different languages use similar rules to truncate adults’ target forms. They
examined the phonological acquisition of French in longitudinal data from one French-speaking child, aged 1; 3-1; 5, and found that the child’s early words were all reduplicated CVCV forms. The examples of English and French children are
presented as below:
English [bənæ nə] → [‘nænə] ‘banana’
French [paˈtat] → [pəˈtæ:] ‘potato’
Child acquiring English produced [bənæ nə] as [‘nænə], and child acquiring French produced [paˈtat] into [pəˈtæ:]. Both English and French children truncated trisyllabic
word into disyllabic word.
2.2 Factors of phonological variability
Variability appears frequently in the developmental phonology literature, and is often used as a diagnostic marker of phonological disorders. However, less is known about normal patterns of variability. The following section introduces the factors of
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phonological variability in typically developing children. Studies concerning phonological variability will also be presented.
Production variability has been attributed to a number of different factors which summarized into the following categories: physical factor and phonological factors.
2.2.1 Physical factor
The development of neuromotor control for speech that occurs during the period of early language acquisition can influence children’s speech production. Young
children have been found to demonstrate high levels of variability in many different aspects of motor control (Green, Moore & Reilly, 2002; Holm, Crosbie & Dodd, 2007;
Macrae, 2013; Sosa & Stoel-Gammon, 2012). In general, motor development might be summarized as a process of increasing accuracy and decreasing variability (Stoel-Gammon, 2006)
Green et al. (2002) investigated the sequential development of the upper lip, lower lip, and jaw movement of 1-, 2-, and 6-year-olds and adults during speech. The findings revealed that 1- and 2-year-old children’s jaw movements were significantly similar to adults’. However, 1-year-olds’ upper and lower lip movement patterns
exhibited high variability, which would become more adult-like with maturation.
These findings suggested that children’s early sound acquisition might be influenced
by the inconsistent development of articulatory control, with the jaw preceding the
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lips. For example, it is easier for children to produce sounds formed by using mandible as primary mover like /b/ than those tend to be associated with lip control like /f/. According to Green et al. (2002), young children’s phonetic inventory was constrained by their dependence on the mandible to approximate adult-like speech targets resulting in the production of predictable speech errors and distortions.
2.2.2 Phonological factors
There are a number of phonological factors of phonological variability to be discussed. The first is phonetic context. The position of sounds in a word may affect the accuracy of production. Kenney and Prather (1986) examined the speech consistency of children aged 2;5 to 5;0. They found that children produced phonemes /t, l, f/ more accurately in word initial than in word final position.
The second phonological factor is phonological overload. It is not surprising that words that are difficult for a child to pronounce will display greater variability.
Leonard et al. (1982) examined 8 typically developing children ranging from 1; 10 to 2;2 years of age. They found that variability is most likely to occur when more than
one phonological or structural feature of the target words that show instability in the child’s linguistic system. Furthermore, words with higher variability rates are most
often those which have more advanced forms, sounds, or word shapes. Thus, variability can be seen as the result of phonological overload, which results in the
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simplification or substitution of sounds that are difficult for children to produce.
The third factor of phonological variability is phonological complexity. McLeod and Hewett (2008) examined variability and accuracy in the production of words containing consonant clusters in typically developing children, aged 2; 0 to 3; 4. They found that the children in the study exhibited extensively variability when producing words that contained consonant clusters.
Macrae (2013) investigated word variability and accuracy in children aged 1; 9 to 3; 1. The study used Word Complexity Measure (Stoel-Gammon, 2012) to assign score to a word based on the three levels of complexity: word pattern, syllable structures and sound classes. The results showed that phonological complexity has a significant positive effect on word variability. Words with more complex speech sounds are produced with more variability than those with less complex speech sounds. These studies are consistent with the study of Ferguson and Farwell (1975) which also indicated the effect of phonological complexity on word variability.
The last factor of phonological factor is reorganization of phonological system.
Sosa and Stoel-Gammon (2006) investigated the patterns of intra-word production variability of English-speaking children during their first year of lexical acquisition (1;0-2;0). The variability pattern observed by Sosa and Stoel-Gammon (2006) showed peaks and valleys. Three of the four children showed a very noticeable peak in
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variability. These peaks appeared when these children aged 1; 9 to 2; 0. It was also the time when two-word utterances were first observed in children’s speech. The results indicated that an increase in variability might correspond to instability in the phonological system when it undergoes reorganization: a movement from lexically-based system of phonological representation to segmental system. This view is consistent with dynamic systems theory, which proposed that variability is associated with transitions between developmental stages and is a potential force of developmental change (Thelen & Bates, 2003).