Speech perception in infancy
One commonly used technique is known is the sucking habituation paradigm. In this procedure, experimenters measure the sucking rate of infants on an artificial teat. Babies prefer novel stimuli, and as they become habituated to the stimulus presented, their rate of sucking declines. If they then detect a change in the stimulus, their sucking rate will increase again. Distributional information about phonetic segments is an important cue in learning to segment speech (Cairns, Shillcock, Chater, & Levy, 1997; Christiansen, Allen & Seidenberg, 1998). Distributional information concerns the way in which sounds co-occur in a language. Very young infants also seem to be sensitive to the prosody of language. Prosodic information concerns the pitch of the voice, its loudness, and the length of sounds. Neonates prefer to listen to parental rather than non-parental speech.
From about the age of 6 months to 10 months, before infants start speaking, they make speech like sounds known as babbling. Babbling is clearly more language-like than other early vocalizations such as crying and cooing, and consists of strings of vowels and consonants combined into sometimes lengthy series of syllables, usually with a great deal of repetition, such as “bababa gugugu”, sometimes with an apparent intonation contour. There are two types of babbling (Oller, 1980). Reduplicated babble is characterized by repetition of consonant-vowel syllables, often producing the same pair for a long time (e.g. “bababababa”). Non-reduplicated or variegated babble is characterized by strings of non-repeated syllables (e.g. “bamido”). The continuity hypothesis (Mowrer, 1960) states that babbling is a direct precursor of language—in babbling the child produces all of the sounds that are to be found in all of the world’s languages. The discontinuity hypothesis states that babbling bears no simple relation to later development. Jakobson (1968) postulated two stages in the development of sounds. In the first stage children babble, producing a wide range of sounds that do not emerge in any particular order and that are not obviously related to later development. The second stage is marked by the sudden disappearance of many sounds that were previously in their repertoires.
Later phonological development
Early speech uses a smaller set of sounds compared with those found in the babbling of just a few months before, but it contains some sounds that were only rarely or not all produced then (particularly clusters of consonants, e.g. “str”). Words are also often changed after they have been mastered.
Smith (1973) described four ways in which children do this, with a general tendency towards producing shorter strings. Young children often omit the final consonant, they reduce consonant clusters, they omit unstressed syllables, and they repeat syllables. Younger children often substitute easier sounds (such as those in the babbling repertoire) for more difficult sounds (those not to be found in the babbling repertoire). A second explanation of output simplification is that children are using phonological rules to change the perceived forms into ones that they can produce (Menn, 1980; Smith, 1973). A third possibility is that simplifications are a by-product of the development of the speech-production system (Gerken, 1994). It is likely that all of these factors play some role.
Harley, Trevor A. (2001). The Psychology of Language From Data to Theory. USA and Canada: Psychology Press Ltd.