2. Children Acquisition
It is from the advanced stage of babbling that children move into uttering their first words. Often this occurs at around 1 year of age but can occur much earlier or much later. When children begin to utter words, somewhat surprisingly only some of the sounds that they have uttered in babbling appear in speech. The other sounds must be reacquired.
And there may be some order to the acquisition of speech sounds. For example, sounds like /x/ (as in Bach), /k/, and /l/ that commonly occurred in vocalization and babbling prior to speech may now tend to occur later, after the acquisition of such phoneme sounds as /p/, /t/, /m/, /a/ ‘fall’, and /o/ ‘tall’. A phoneme, it should be said, represents a class of speech sounds in a language. For example, in the word ‘pep’ the individual sound
/p/ can represent the sound at the beginning of the word ‘pep’ as well as the sound at the end of the word ‘pep’. (Incidentally, the letters surrounded by slashes (//) indicate that a phoneme sound is identified. A phoneme sound is a single discrete sound of a language.) Phonetically, the two sounds are different, with /p/ in the final position having a large amount of aspira- tion (puff of air). Nevertheless, they are regarded as the same phoneme. There is, then, some discontinuity between babbling and meaningful speech
where the kinds of sounds that occur in babbling are not always immedi- ately realized in meaningful speech.
While some studies show some continuity between babbling and early speech (Vihman et al., 1985), most research shows a lack of continuity, e.g. Oller and Eilers (1982), Stoel-Gammon and Cooper (1984), and Kent and Bauer (1985), in that advanced babbling seems to approach the consonant– vowel combinations of later meaningful speech. The relationship, however, is not a strong one.
Why is there some degree of discontinuity from babbling to the production of speech sounds? In our view, the discontinuity issue involves, as Jesperson (1933) noted many years ago, the distinction between intentional and non- intentional vocalization. Babbling is non-intentional in the sense that par- ticular sounds are not under central cognitive control; the infant does not intentionally make the particular babbling sounds that occur. They seem to happen by the chance coordination of speech articulators (various parts of the body that are used to create speech sounds: mouth, lips, tongue, vocal cords, etc.). The case of meaningful speech is quite different. Here, sounds must not be uttered at random but must match previously heard sounds that are conventionally associated with certain objects, needs, and so forth. In order to accomplish this feat, it is necessary that the child discover which sound is created by which speech articulators. It is this knowledge that the child must acquire in order to speak meaningfully. Speech is dependent to some degree on babbling, however, for it is in engaging in babbling that the child will chance on many of the various articulatory mechanisms for producing speech and give practice to the use of those articulators.
1.1.1.2 Explaining the acquisition order of consonants and vowels
In the meaningful speech phase, it appears that consonants are acquired in a front-to-back order, where ‘front’ and ‘back’ refer to the origin of the articulation of the sound. Thus, /m/, /p/, /b/, /t/, and /d/ tend to precede
/k/, and /x/. Conversely, vowels seem to be acquired in a back-to-front order, with /a/ (ball) and /o/ (tall) preceding /i/ (meet) and /√/ (mud). Jacobson (1968) devised a theory based on his distinctive feature theory of phonological oppositions that attempts to predict the order of the acquisi- tion of speech sounds. In the main, however, empirical studies have not supported his predictions (Velten, 1943; Leopold, 1947; Braine, 1971; Ferguson and Garnica, 1975). There is much more variation in the order of acquisition than the theory predicts. Actually, this may well be expected, since there could be a great deal of chance involved when a child searches for the proper articulators of speech with which to make a sound.
As far as the establishment of intentional connections is concerned, our opinion is that two variables dominate this process: visibility of articulators and ease of articulation (first proposed by Steinberg, 1982). When the child becomes motivated to produce meaningful speech (this occurs after the
child has learned to understand some words spoken by other people), the child begins to seek ways to produce the desired sounds. The child then becomes alert to clues that relate to the articulation of the speech sounds.
The child observes where speech sounds come from and notes the relationship between the sounds and the position of noticeable speech articulators, particularly the mouth and lips (Kuhl and Meltzoff, 1988; Legerstee, 1990). It is mainly movements that the child observes and imitates. Since noticeable mouth and lip movements are primarily involved in the articulation of certain consonants, it is not surprising, therefore, that chil- dren tend to produce these consonants, such as /m/, /p/, and /b/, before the others. Consonant sounds like the stop /k/ and the fricatives /s/ and
/z/, which involve the movement of non-visible articulators, are generally learned later.
As for vowels, since most involve the use of largely unseen articulators, children get little aid from direct observation. Rather, they must indulge in a lot of trial and error in order to secure the proper positions for articulators. It seems that those sounds that are closest to the resting position of arti- culators, e.g. back vowels such as /a/ (watch), are easier to create and are learned earlier while those sounds that require more motor control to create,
e.g. a tensed front vowel such as /i/ (feet), are learned later.
However, over and above the operation of these variables of ease and visibility, there is (as first mentioned above) the important one of chance. It seems that children may discover by chance a particular articulator–sound connection, e.g. the daughter of Leopold (1953), Hildegard, was able to pro- nounce the word ‘pretty’ with precision yet she was unable to pronounce other words composed of similar sounds. Interestingly, although the word ‘pretty’ was pronounced accurately at first, over time, as her pronunciation of words developed, the pronunciation of that word deteriorated. It seems that if a word is to be retained, the chance discovery of an articulator–sound connection must be followed by its incorporation within the overall develop- ing sound system.