Typical Development of Prelinguistic Vocalization

Transcription

1 Typical Development of Prelinguistic Vocalization Patterns Across Languages Bilinguistics, Inc. This course is offered by Bilinguistics, an ASHA Approved CE Provider Content Area: Basic Communication Processes Instructional Level: Intermediate Continuing Education Units:.1 Objectives: Participants will be able to demonstrate knowledge in and identify: Basic acquisition of speech sounds at the pre-linguistic level Sound acquisition norms that are universal to all languages Common consonant and vowel patterns that are produced during babbling An understanding of suggested stages of sound acquisition Frequency of initial consonant use and consonant-vowel co-occurrence 1

2 Introduction The development of the sound system leading up to the production of words has been well documented (Oller, 1980; Stark, 1980; Vihman, Macken, Miller, Simmons, & Miller, 1985; Vihman, Ferguson, & Elbert 1986). Data exist concerning the order in which speech sounds and sequences emerge (Davis, & MacNeilage, 1995; Elbers, 1982), the make-up of sound segments (Nathani & Oller, 2001; Mitchell & Kent, 1990), as well as the function of the speech mechanism when producing sounds (Davis & MacNeilage, 1995; MacNeilage, Davis, Kinney, & Matyear, 2000). An understanding of typical speech development is essential in order to identify the differences in early vocal development when a disorder is present (e.g. loss of hearing), and to understand when developmental processes are influenced by a second language. For the purpose of this paper, speech development will be categorized and defined as, pre-linguistic vocalizations and canonical babbling. Pre-linguistic vocalizations refer to vegetative and non-vegetative sounds. Canonical babbling refers to patterned, minimally consonant-vowel (C-V) combinations such as CV, VC, or CVCV that meet the rhythmic requirements for sounding speech-like (Oller, 1980). Canonical babbling will include all vocalizations traditionally defined as reduplicated and variegated sequences meeting the timing requirements for being perceived as speech-like. The Emergence of the Sounds of Speech The complexities of speech find their roots in the simplified sounds produced by infants as young as six months of age (Nathani & Oller, 2001). Previously, it was accepted that infant vocalizations that are recognizable as speech were not connected to sound patterns in first words. However, this idea of discontinuity, as first suggested by 2

3 Jakobson in 1941, has been refuted by recent research showing continual development from babbling through to speech (Vihman et al., 1985). In both babbling and early words, stop consonants (e.g. /b/,/d/) are frequent and there is an absence of consonant clusters (Nathani & Oller, 2001). With research on the emergence of sounds in speech in infancy, Oller (1980) created a hierarchy of pre-linguistic speech development that continues to be widely accepted. His goal was to include the many characteristics of spoken languages and provide a way for any infant sound to be described in terms of crucial speech parameters (Oller, 1980). He realized this by analyzing aspects of speech such as pitch, tone, quality, and timing instead of relying heavily on phonological transcription (Oller, 1980). Earlier, empirical research in the 1940s (e.g. Jakobson) failed in its attempt to find relations between adult and infant speech patterns due to strict use of phonetic transcription (Nathani & Oller, 2001). Previously, speech-like (i.e. ba) and non-speech-like (i.e. a burp) sounds were collapsed into the same category using the International Phonetic Alphabet (IPA), which made any difference or similarity indistinguishable. Therefore, Oller analyzed speech based on larger properties and defined five stages of speech development occurring in the first year of life. 3

4 Table 1: The Emergence of the Sounds of Speech in Infancy. Stage Age (in months) Type Stage 1: The Phonation Stage 0-1 Vowels, consonants, throaty sounds, and phonation with a closed mouth Stage 2: The Goo Stage Stage 3: The Expansion Stage Stage 4: The Canonical Stage Stage 5: The Variegated Babble Stage Note: Adapted from Oller (1980). 2-3 Velar (/k/ and /g/) consonants 4-6 Strong vowels, bilabial trills, squeals, growling 7-10 Patterned, consonant-vowel combinations, reduplicated babble (mama), and nonreduplicated (ada) Diverse babble (bada), gibberish, intonation Speech development begins when babbling takes on adult-like prosody and form (Nathani & Oller, 2001). Babbling, as defined by Oller (1980), begins at a stage where consonant and vowel sequences conform to rhythmic patterns perceived as speech-like in timing. Prior to babbling, the precanonical sound qualities such as grunts, squeals, and gooing (Stages 1,2, & 3), are most likely reflexive or accompany distress. These sounds do not follow any linguistic rules and do not make use of the full potential of the vocal tract (Nathani & Oller, 2001). En route to producing discernable words, canonical babbling begins at around seven months (Oller, 1980). The timing characteristics of a child s speech become relatively rigid and syllable structure begins to resemble mature language. Productions are either non-reduplicated (/abid/) or reduplicated (/mama/) and may be perceived by adults as words (Oller, 1980). The progression from canonical to variegated babble marks a giant shift from prelinguistic to linguistic behavior (Mitchell & Kent, 1990). Repetitive sound clusters 4

5 diminish and there is an increase in the variety of consonants and vowels within utterances (Mitchell & Kent, 1990). Perceivable changes in intonation (Elbers, 1982 ) are accompanied by phonetically-varied reduplicated (dudududu) and non-reduplicated (dudi) forms (Mitchell & Kent, 1990). Diphthongs emerge as well as jargon that resembles the ambient language (Elbers, 1982). While Oller s explanation of emerging sounds is widely accepted, some researchers feel that speech development cannot easily be divided and categorized. Stark (1980) suggested that so much development is occurring simultaneously during the canonical and expansion stages (Oller Stages 3 and 4) that linguistic development around twelve months cannot be divided. In her assessment of speech development within the first year (See following table), Stark (1980) demonstrated that speech development could be illustrated logically using four stages. Stages 1 through 3 mirror the work done by Oller (1980) but stage 4 is a combination of the canonical and variegated babble stage. In Stage 4, the infant is making use of CV patterns, reduplicated and non-reduplicated babble, gibberish and intonation. There is not one fixed point in time where one process ends and another replaces it. Stark argues that there is a transition between vocalizations and employing sounds in a speech-like manner (Stark, 1980). 5

6 Table 2: Speech Development in the First Year. Stage Class Type 1 Vegetative function Crying, fussing, nasal (closed mouth) phonation 2 Cooing sounds First voicing, pleasure, laughter, nasal sounds, velar sounds 3 Vocal play Vocalic and consonant elements, frication, nasal murmurs 4 Mastery of speech-like activity Babbling, controlled CV transitions, reduplicated and non-reduplicated sounds Note: Adapted from Stark (1980). Babbling is the culmination of development that precedes meaningful speech (Vihman et al. 1985). In a typically developing child, babbling begins around 7 to 10 months and speech emerges from this initial use of consonant and vowel structures. However, in a child who is hearing-impaired, development is not only delayed but may have a unique pattern. When investigating these differences in a child with hearing impairment, one must first understand why speech develops in typically developing children. Theories on Speech Development Theories vary widely accounting for how and why the speech mechanism develops to eventually produce meaningful speech. While it is now generally accepted that sound qualities in canonical babbling are continuous with sound qualities in the early word period (Vihman et al. 1985), there are varying theories as to why pre-verbal vocalizations and canonical babbling take place. 6

7 In order to account for babbling s influence on speech, a theory must take into account the reduplicated, dependable nature of babbling, the maturation of the sound system in proportion to growth, the adult-like speech it imitates and then becomes, and the universal nature of babbling in its initial stages. Davis et al. (2002) address these issues biologically in terms of the frame/content theory. The content (consonants and vowels) of an utterance is placed within a frame (oscillation of the mandible). The movement of the frame is believed to have emerged from reflexive motions of ingestion such as eating and sucking. Vowels (V) evolve from the open aspect of mandibular movements where as the closing phase creates a consonant (C) (Davis et al. 2002). Canonical babbling, once again, is a sequence of successive syllables, and is characterized by both reduplication and variegation in vocal sequences (Stark, 1980; Elbers, 1982; Oller, 1980). In tying frame/content to babbling s relation to speech, rhythmic open and closed states (CV or VC) create a temporal regularity that is perceived by adults as speech-like (MacNeilage & Davis, 1990). As maturation changes the physical articulatory structures, babbling is enhanced. In canonical babbling s initial stage, the tongue and lips are seldom employed, relying on the mandible for the full range of motion (Davis & MacNeilage, 1995). Changes in amplitude of the mandibular cycle would result in height changes for vowels (e.g. [ae] verses [i]) and manner changes for consonants (e.g., [d] versus [j]) (Davis & MacNeilage; 3, 1995). Alternations between oral and nasal sounds appear when control is gained over soft palate closure. The basis of babbling exists within the timing and development of the action and not in descriptions of phonological representations (Davis & MacNeilage, 1995). 7

8 Biological assertions relating physical movements to speech cannot be language specific or dependent. That is to say, results should be universally challengeable and provide similar outcomes across an array of ambient languages. MacNeilage et al. (2000) suggest that in early development an infant babbles in similar patterns regardless of ambient language. In their study on serial organization in infants across languages, MacNeilage and colleagues (2000) explore consistencies in babbling productions and compare data across languages. Six language populations (English, French, Swedish, Japanese, Brazilian Portuguese, & Quichua) and one infant with deafness who had received a cochlear implant were studied, yielding babbling patterns that contain some universal consistencies (MacNeilage et al. 2000). The frame/content theory suggests that it is initially important to understand the frame (mandibular oscillation) that establishes the rhythmic alteration between consonants and vowels. The content (vowel and consonant) of each oscillation can then be scrutinized separately and quantified in syllables (CV, VC) that each content pair forms (MacNeilage et al. 2000). Consistencies in babbling have been reported across different language populations and one implanted child (MacNeilage et al. 2000). These consistencies are also present when hearing-impairment and language differences are combined (Moore et al. 2007). Speech Content The fundamental questions for interventionists relate to what vocalization patterns occur at what age relative to typical developmental expectations, as well as what might be the cause if a child is not producing these vocalization patterns. These questions are addressed by identifying the type, number, and developmental sequence of vowels and 8

9 consonants within a child s repertoire. Independent research studies have described the content and framework of early speech and collectively offer a greater understanding of babbling and its developmental sequence. Vowels Vowels exceed the number of consonants produced during babbling for most children (Davis & MacNeilage, 1995). While no vowel pattern characterizes every child (Davis & MacNeilage, 1995), certain tendencies exist universally. Children who are babbling have a propensity to use mid-front (head), low-front (had), and central vowels (hut)(davis & MacNeilage, 1995). As illustrated in the vowel chart below, a vowel s designation is derived from the manner (height) in which the jaw is open and the position of the tongue (front to back) when the vowel is produced. There is a tendency for children to begin producing front vowels and shift back in the mouth as maturation occurs (Oller, 1980). Low back vowels are not often produced until later in development (Oller, 1980). Although vowels represent a greater portion of an infant s utterances, it is the consonant that is usually interpreted as carrying the speech message. Table 3: Vowel Chart Indicates direction of acquisition over time. Indicates most common vowels found in babbling. 9

10 Consonants Like vowels, the first consonants that are produced are guided by the constraints of physical development. Stop consonants (/b, p, t, d, g, k/) and nasal consonants (/m, n, ŋ/) are the most common that are produced during babbling across languages (Vihman, 1985; Locke, 1983; Davis & MacNeilage, 1995). The production of these sounds is physiologically similar in that they are all produced with a total occlusion of the oral cavity. The nasal consonants differ in that the nasal passage remains open during the sound s production (Davis & MacNeilage, 1995). Hearing children produce mostly oral consonants by the onset of babbling (Davis & MacNeilage, 1995) Consonant frequencies are determined by how easily the sound can be produced as well as where in the oral cavity it occurs. Infants initially have a greater facility with front consonants such as the alveolars (/d, t/), and labials (/m, b, p/) (Locke, 1983). The alveolar /d/ is found to be the largest category present in a study of six infants by Davis and MacNeilage in Nasals (/m, n, ŋ/) and glides (/w, j/), occur less frequently than stop consonants (Locke,1983; Davis & MacNeilage, 1995), and velars (/g, k/), produced by the tongue and the back of the throat, have very little incidence. Complex sounds such as liquids (/l, r/) and consonant clusters are infrequent or are not present (Vihman, 1985). Locke s study (1983) of consonant frequency illustrates the prevalence of consonants within an infant s sound repertoire (See Table 4). He found all six stop consonants to be frequent, both glides, as well as an appearance of the first fricative (/s/). This study additionally provides information about the role that voicing plays in babbling. The more common sounds, with the exception of the glottal /h/, were all voiced. Within each minimal pair (two sounds that share the same articulatory 10

11 movements) the voiced sound was normally present more often (Locke, 1983). What Davis and MacNeilage (1995) and Locke (1983) suggest bases phonemic development on maturation. Theoretically, consonant inventories and prelinguistic vocalizations of this study s participant should be commensurate with these previous findings independent of ambient language. Table 4: Consonant Frequency. This chart illustrates the percentage that time that each consonant was present during sound sampling. More Frequent Consonants Less Frequent Consonants Sound A Sound A h 31.77% v 1.03% d l 0.96 b 9.79 θ 0.85 m 6.69 z 0.56 t 4.34 f 0.37 g 4.15 ʃ 0.37 s 3.45 ð 0.34 w 3.39 ŋ 0.33 n 2.65 Ʒ 0.1 k 2.12 r 0.1 j 1.77 ƫƒ 0 p 1.63 ʤ 0 Totals 92.33% Totals 5% Note: From Locke (1983). 11

12 Consonant Vowel Co-occurrences The combination of vowels and consonants create the syllable patterns that are often perceived as speech. Early in babbling, three common patterns appear to be universal (MacNeilage & Davis, 2000). Most often, labial consonants occur with central vowels (/bλ/), alveolars occur with front vowels (/dæ/), and velars occur with back vowels (/gu/) (Davis & MacNeilage, 1995). In the case where labial consonants occur with central vowels, it is known as a pure frame (MacNeilage et al., 2000, MacNeilage & Davis, 2000). It is pure in the sense that the sound is solely the result of mandibular movement. The consonant is formed as the lips come together and the vowel is formed while the tongue is in a resting position (MacNeilage & Davis, 2000). Figure 2 illustrates the oral positions of these CV co-occurrences. Syllables appear in an infant s repertoire as monosyllables (Vihman, 1985). Normally these syllables begin with a consonant and end with a vowel (MacNeilage, Davis, Kinney, & Matyear, 2000). MacNeilage et al. (2000) state that the CV sequence is so important that it is often given the status of the only universal syllable type (MacNeilage et al.; 154, 2000). Following the appearance of these syllables in isolation, an infant begins to reduplicate (Oller, 1983). 12

13 Table 5: Consonant Vowel Co-occurrence Constraints in Babbling. Note: From MacNeilage & Davis, (2000). Reduplicated syllable production (babbling) is the result of repeated oscillations of the mandible (Davis & MacNeilage, 1995). Mandibular movements appear earlier than lingual or labial movements in canonical babbling (Davis & MacNeilage, 1995, Davis et al., 2002) because oscillation is easiest when the articulators stay in one place (Davis & MacNeilage, 1995; MacNeilage and Davis, 2000; MacNeilage, 2000). Initially, 50% of the total syllable is reduplicated and 67% of the consonants are reduplicated (Davis and MacNeilage, 1995). As the child starts to produce his or her first words, 30% of the total syllables are reduplicated and 73% of the consonants are reduplicated (MacNeilage, Davis & Matyear, 1997). As variegated babble leads into full words, there is a very little reduplication in the child s attempts at speech (MacNeilage, Davis, Kinney, & Matyear, 2000). 13

14 Table 6: Observed-to-Expected Frequencies of Consonant-Vowel Co-occurrence. Consonants Vowels Coronal Labial Dorsal Front B C W Central B C W Back B C W Note: B = prespeech babbling, C = babbling concurrent with first words, W = first words. Taken from: MacNeilage et al.; p.155 (2000).\ Summary and Conclusion In conclusion, prelinguistic babbling is the biological result of mandibular oscillations that are accompanied by phonation (Davis & MacNeilage, 1995; MacNeilage and Davis, 2000; MacNeilage, 2000). Many of these syllable patterns that are created during babbling are universal, without influence of ambient (native) language (MacNeilage, 2000). This being said, an explanation of speech development, even for a 14

15 Spanish-speaking child, for example, would be generic up until babbling makes the transition into first words (Oller, 1980; Locke, 1983). References Davis, B.L., MacNeilage, P.F., & Matyear, C.L. (2002). Acquisition of serial complexity in speech production: a comparison of phonetic and phonological approaches to first word productions. Phontica, Davis, B.L., & MacNeilage, P.F. (1995). The articulatory basis for babbling. Journal of Speech and Hearing Research, 38(6), Elbers, L. (1982). Operating principles in repetitive babbling: a cognitive continuity approach. Cognition, 12, Locke, J.L. (1983). Phonological acquisition and change. New York: Academic Press. MacNeilage, P.F., Davis, B.L., Kinney, A., & Matyear, C.L. (2000). The motor core of speech: A comparison of serial organization patterns in infants and languages. Child Development, 71(1), MacNeilage, P.F., Davis, B.L., & Matyear, C.L. (1997). Babbling and first words: Phonetic similarities and differences. Speech Communication, 22, Mitchell, P.R., & Kent, R.D. (1990). Phonetic variation in multisyllable babbling. Journal of Child Language, 17, Moore, J.A., Prath, S., Arrieta, A. (2007). Early Spanish Speech Acquisition Following Cochlear Implantation. The Volta Review, 106(3), Nathani, S., Oller, K. (2001). Beyond ba-ba and gu-gu: challenges and strategies in coding infant vocalizations. Behavior Research Methods, Instruments and Computers, 33(3),

16 Oller, D.K. (1980). The emergence of the sounds of speech in infancy; Chapter 6. In G. Yeni-Komshian, J.F. Kavanagh, & C.A. Ferguson (eds.), Child Phonology: Vol. 1. Production (pp ). New York, Academic Press. Stark, R.E. (1980). Stages of speech development in the first year of life. In G. Yeni- Komshian, J.F. Kavanagh, & C.A. Ferguson (Eds.), Child Phonology: Vol. 1. Production (pp ). New York, Academic Press. Vihman, M.M., Macken, M.A., Miller, R., Simmons, H., & Miller, J. (1985). From babbling to speech: A re-assessment of the continuity issue. Language. 61(2), Vihman, M.M., Ferguson, C.A., & Elbert, M. (1986). Phonological development from babbling to speech: common tendencies and individual differences. Applied Psycholinguistics, 7,