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Pitch characteristics of Japanese maternal speech to infants Nobuo Masataka Journal of Child Language / Volume 19 / Issue 02 / June 1992, pp 213 - 223 DOI: 10.1017/S0305000900011399, Published online: 17 February 2009
Link to this article: http://journals.cambridge.org/abstract_S0305000900011399 How to cite this article: Nobuo Masataka (1992). Pitch characteristics of Japanese maternal speech to infants. Journal of Child Language, 19, pp 213-223 doi:10.1017/ S0305000900011399 Request Permissions : Click here
Downloaded from http://journals.cambridge.org/JCL, IP address: 138.251.14.35 on 17 May 2015
. Child Lang. 19 (1992), 213-223. Printed in Great Britain
Pitch characteristics of Japanese maternal speech to infants* NOBUO MASATAKA The University of Tokyo (Received 25 June 1990. Revised 12 April 1991)
ABSTRACT
The fundamental frequency F o patterns of maternal speech addressed to infants aged 053-0; 4 were measured quantitatively. Speech samples were recorded when six Japanese-speaking mothers addressed an adult and their own infants. Japanese mothers speaking to adults use a relatively restricted F o range, concentrated around the mother's F o , which tends to be near the low end of the total range used. These acoustic characteristics are not altered substantially when these same women speak to their infants in initial utterances to attract the infants' attention. If such attempts are unsuccessful, however, they are likely to make more exaggerated utterances, in which F o shifts upward and the frequency range is significantly increased. Moreover, only when acoustic characteristics of maternal speech to infants are exaggerated, can the type of F o contour of the infant's subsequent response be predicted to a significant extent from the mother's preceding utterance.
INTRODUCTION
There is a growing literature on paralinguistic or prosodic features of parental speech to infants (Garnica, 1977; Newport, Gleitman & Gleitman, 1977; Papousek, Papousek & Bornstein, 1985). The studies report that adult speech to infants is characterized by a higher overall pitch, wider pitch excursions, more distinctive pitch contours, slower tempo and longer pauses than in normal adult conversation. Cross-linguistic research has documented common patterns of such exaggerated features in parental speech to infants younger than age o;8 across a number of European languages and Japanese (Fernald, Taeschner, Dunn, Papousek, Boysson-Bardies & Fukui, 1989) and in maternal speech in Mandarin Chinese (Grieser & Kuhl, 1988). These [•] I thank Shozo Kojima and Toshikazu Hasegawa for their help in conducting this research. I am grateful to Katharine Perera and two anonymous reviewers for making invaluable comments. Address for correspondence: Nobuo Masataka, Department of Anthropology, Faculty of Science, The University of Tokyo, Hongo, Bunkyo, Tokyo 113, Japan. 213 9
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features are thought to serve several functions related to language development. In particular the use of exaggerated acoustic characteristics in the early preverbal period has been assumed to function primarily to engage the infant's attention and maintain social interaction. Using a conditioned headturning procedure, Fernald (1985) showed that infants aged o;4 turned their heads more often towards a recording of female infant-directed speech than female adult-directed speech. Werker & McLeod (1989) measured the amount of time infants aged 0:4-0; 5 and infants aged 017-059 viewed a television monitor^ that presented either a female or a male actor speaking infant-directed or adult-directed speech. They found that both groups of infants watched the monitor longer when infant-directed speech was being presented. In this paper, further evidence is presented for the attention-getting properties of infant-directed intonation. It is well-known that for a-child to engage in joint action with a parent, considerable interactional support by the parent is necessary, especially in the beginning phases of joint action. Parents have to repeat their attempts to elicit vocal responses from infants as long as the infants remain unresponsive. This study undertook acoustical analyses on sequences of utterances as mothers attempted to get vocal behaviour from their infants. The analysis concentrated on fundamental frequency (Fo) patterns. The results reveal that mothers apparently alter the pitch charac. teristics of their speech in sequences of repeated utterances addressed to their infants. I also examined whether the change in maternal pitch could differentially affect acoustic features of pitch in immediately subsequent infant utterances. In terms of F o contours, I examined how well the type of subsequent infant vocalizations could be predicted from the type of immediately preceding maternal speech, using G-tests of goodness of fit (Sokal & Rohlf, 1981). METHOD
Subjects The subjects were six monolingual women who spoke only Japanese. All of the women were full-time housewives between the ages of 24 and 29. Each subject was the mother of a firstborn male infant aged o 13-0 54. The infants were healthy and had uncomplicated prenatal and perinatal histories. Procedure Each mother was recorded in her home as she spoke to her infant and as she telephoned a Japanese-speaking friend. Studies have shown that there are no significant differences between the prosodic features of maternal speech samples collected at home as opposed to in a laboratory setting (Stern, Spieker, Barnett & MacKain, 1983). Recordings were made with the mother 214
JAPANESE MOTHERESE
seated in a chair next to a studio-quality portable tape recorder (Sony TCD5M). The mother and the infant each wore a high quality lapel microphone (Sony ECM16). Inputs from the microphone were mixed and recorded on one channel of the tape recorder. The order of the listener conditions was counterbalanced across subjects. Mothers were told that their speech in different settings was of interest, but not specifically that characteristics related to its F o features would be analysed. Adult-to-Adult (A-A) speech. When adults speak to other adults, the speech of the two speakers tends to overlap, obscuring the acoustic features of interest. Recordings made while the speaker is talking to someone over the telephone eliminate this problem because the second speaker is not recorded. Comparison recordings were made in which the mother spoke with a native speaker in person or over the telephone; these tapes verified that equally typical speech could be sampled under both recording procedures. The mother prearranged to telephone a friend during our visit. Each mother was left alone in the room during the telephone conversation and was recorded for 15 minutes. Adult-to-Infant (A—I) speech. Each mother held her infant on her lap as she sat in the chair. The observer instructed the mother to talk to her infant as she normally might when they were alone together. The mother and infant were left alone in the room for the duration of the recording and were recorded for 15 minutes in a given recording session. For each mother-infant dyad, a total of three sessions was undertaken. In each session, episodes of interaction were identified; episodes being defined as series of rounds with a focus on a specific topic, set off by periods of verbal inactivity. Episodes were ultimately constrained by the infant's attention. Episodes began with the mother attempting to attract her infant's attention through speech. As a unit for acoustic measurements, an utterance was operationally defined as a continuous vocalization of a mother or an infant bounded by pauses of longer than 0-3 sec. Thus two complete run-on sentences by a mother without an intervening pause were scored as an utterance. All meaningful communicative vocalizations were considered as words, e.g. ooh, aah and hmm. Non-verbal sounds (kisses, laughter) and routines (songs, nursery rhymes) were excluded. If an infant vocalized within 3-0 sec of an utterance by its mother, that was counted as an infant response and the mother's utterance was the beginning of an episode. The mother's utterance in each such episode was defined as an 'initial maternal utterance'. If the mother was unsuccessful, she made only a few utterances, punctuated by silence on the infant's part. Even when she was successful, she frequently had to make more than one utterance before the infant responded. Once the infant responded, the mother would continue the vocal interactions as long as the infant remained attentive and responsive. When the infant turned his attention elsewhere, the episode would end. The mother 215 9-2
CHILD LANGUAGE
would then wait several minutes before initiating a new episode. For analysis of speech features, only the initial maternal utterance and the initial vocal response of the infant to that utterance in each A-I episode were used. The number of utterances the mother required to initiate the episode was also counted. Acoustic measurements (1) Fo measures Analysis of F o was performed on all utterances recorded in A-A speech and all initial maternal utterances (defined above) in A-I speech for each subject, using a Kay DSP Sonagraph (Model 5500—1) with 150 Hz band filter and frequency scale up to 4000 Hz, connected to a PDP 11/23 computer. The sonagraph was set to measure F o value (with accuracy of + 1 Hz) for each 20 msec of voiced speech by means of Fast Fourier Transformation. The information obtained was stored in the PDP computer, which calculated average F o (the mean of the distribution of values for each utterance) and F o range (maximum minus minimum values for each utterance). (2) F o contour classification Previous studies have noted that the intonation contour typical of infant-directed speech can be classified according to the extent and direction of the frequency excursion (Stern, Spieker & MacKain, 1982; Stern, Spieker, Barnett & MacKain, 1983; Fernald & Simon, 1984; Grieser & Kuhl, 1988). In this study, therefore, I performed F o contour classification on all initial maternal utterances in A-I speech and infant's initial responses to them, using five categories of F 0 -contour type: RISING, FALLING, FLAT, BELL-SHAPED, and COMPLEX. In order to classify contour types, sonagrams produced were visually inspected. All of the contours were categorized as one of the five 'prototypical patterns'. Altogether, four raters coded the utterances: two of them coded the mothers' vocalizations and the other two coded the infant vocalizations. None of them was informed of the purpose of the present study. Inter-rater reliability, defined as the percentage of instances for which there was agreement on the classification of contour type, was greater than 90%. For cases in which there was disagreement, the two judges re-examined the contours together and decided how they should be classified. Rising and falling contours were often marked by only relatively small upward and downward frequency shifts, respectively. However, a pitch rise or fall was recognized only when the value of a frequency-modulation range of a continuous slope exceeded 15 Hz in maternal vocalizations, and 10 Hz in infant vocalizations, which are narrower in range.
216
JAPANESE MOTHERESE
(a)
Adult-to-infant speech
200-
Adult-to-adult speech
i
I
I
I
I
(b) Adult-to-infant speech 50Adult-to-adult speech
1 2 3 4 ^ 5 No. of maternal utterances before infant response Fig. i. Average pitch (a) and pitch range (b) for initial maternal utterances in A-I speech. (Average values of the mothers' utterances in A-A speech are given by the horizontal straight lines.) RESULTS
FQ measures
Figure i presents the average F o and F o range for all the subjects' utterances in A-A speech and all initial maternal utterances in A-I speech. For A-I speech the data are presented in terms of the number of utterances the mother made before successful elicitation of the infant's response in each episode (represented on the abscissa of Fig. i). Detailed individual data are shown in Table i. Comparisons of the average F o for A-A speech and A-I speech showed that, overall, the mothers' average F o in the A-I condition exceeded that observed in the A-A condition. Examining the F o values between the two conditions, a single classification ANOVA showed that there was a significant difference, F(i, 5) = i8 - 4i, p < o-oi. However, follow-up t tests revealed that each subject demonstrated a significant increase in her F o values only when she made more than two utterances before elicitation of the infant's response (/> < o - oi, in all cases). When the first one or two utterances by the mother were responded to by the infant, the F o did not differ significantly from that observed in the A-A condition (p > o-io, in all cases). 217
CHILD LANGUAGE
i. Mean values of average Fo and Fo range in individual subjects' utterances in the A-A and A-I conditions {with s.D. in brackets)
TABLE
A—I condition
Number of maternal utterances before infant response Parameter/ Subject No.
A-A condition
i
2
3
4
I75(i7)
181 (20)
234(19)
236(25)
252 (28)
177(15)
2
199(20)
3 4 5 6
212 (23)
216(18) 208(15) 206 (23) 213(30) 206 (29)
272 (28) 235 (22) 255(48) 240 (22) 226(10)
288(30) 296 (23) 260 (43) 273 (27) 254(35)
202 (26) 195 (10) 189(16) 196(18)
Average Fo (Hz)
F o range (Hz) 2
3 4
5 6
20 (4-2)
26 (6-s)
71 (224)
245 (26) 243 (18) 289(52) 266(31) 257('7) 77 (160)
75 (>93)
18 (27)
i9(3-3) 23 (6-4)
30 (7-o) 25 (3-6) 24 (2-7) 26 (20) 20(1-9)
83 (287) 55 (32-2) 67 (200) 66(145) 51 (126)
75 (205) 98 (250) 92 (25-8) 104(28-9) 80 (16-6) i°7 (365) 78 (223) 86 (342) 71 (180) 88 (235)
23 (4'5) 31 (60)
203 (16) 187(15) 208(19)
28(31) 17(1-6) 18 ( 2 2 )
193(23)
24 (38) 16 (1-2)
22 (37)
Similar results were obtained from the analysis of the F o range for A-A speech and A-I speech. An ANOVA revealed that there was a significant difference in the F o range values between the A-A condition and the A-I condition, F ( i , 5) = 19-25,/) < o-oi. Overall, the F o range for the six subjects in the A-I condition exceeded that observed in the A-A condition. Again, follow-up t tests revealed that each subject demonstrated a significant increase in her F o range values only when she made more than two utterances before the infant's response (p < o-oi, in all cases). When only one or two utterances were made by the mother before the response, the F o range values did not differ significantly from that observed in the A-A condition (J> > o-io, in all cases). F o contour classification The results described above indicate that acoustic characteristics which have been reported to be typical of motherese are also displayed by the subjects in the present study. Does exaggerated maternal speech elicit an infant's response in a different manner from that in which less exaggerated speech does ? In order to examine this, the following analysis was undertaken. I hypothesized that the F o contour of exaggerated maternal speech could significantly affect the F o contour of immediately subsequent infant vocalizations, but that the F o of less exaggerated speech would not be able to do so. Therefore, the following analyses were conducted independently on two 218
JAPANESE MOTHERESE
2. Distribution of maternal speech/infant's response sequences when the mother made only one or two utterances before infant's response
TABLE
Contour type of subsequent infant 's response initial maternal utterance Rising (AT = 2 5 1 )
Falling (AT = 2 8 1 )
Bell-shaped (iV=i 47 )
Flat or Complex (N= 166) Total N
Rising
Falling
Bell-shaped
Flat or Complex
72
88 (9i-5)
4> (425)
(49-0)
50
(680) 77 (762) 37
102
51
51
(102-4) 63
(476)
(549)
22
25
(39-8)
(53-6)
(24-9)
(287) 39 (32-4)
43
55
(4S'O)
(6o-5)
229
308
29
(280) 143
165
G(9) = 564, p > o-io. Expected values calculated from marginal totals are given in parentheses.
3. Distribution of maternal speech/infant's response sequences when the mother made more than two utterances before infant's response
TABLE
Contour type of subsequent infant 's response initial maternal utterance Rising
Rising 114
Falling 73
(786)
Bell-shaped
Flat or Complex
23
9 (269) 8 (23-2) 7
(AT = 219)
(691)
Falling (AT =189) Bell-shaped
44
109
28
(597)
(675)
(38-3)
29
(AT = 1 0 7 )
(33-8)
55 (217)
Flat or Complex (AT=
Total N
112)
16
(384)
(44-4)
24
14
21
(35-4)
(402)
(22-7)
198
225
127
(3i-0 53 (13-8) 77
G(9) = 239-5, p < o o o i . Expected values calculated from marginal totals are given in parentheses.
different subsets of the data, classified according to the following criteria. (1) when the mother made only one or two utterances before her infant responded (N = 845); (2) when the mother made more than two utterances before her infant responded (N = 627). All contours occurring in the maternal and infant utterances were classified according to the five contour types described above. In all, rising contours accounted for 32 % in maternal speech and for 29% in infant speech, and falling contours for 32% in maternal speech and for 36% in infant speech. Bell-shaped contours containing both a rise and a fall accounted for 17% of the data in maternal 219
CHILD LANGUAGE
speech and for 18 % of the data in infant speech. The remaining two contour types, complex and flat, only occurred less than 10% of the time in both maternal and infant speech. Those latter two types have therefore been combined in Tables 2 and 3. Table 2 presents the distribution of maternal speech/infant response sequences when the mother made only one or two utterances before the infant's response. The distribution did not deviate significantly from that predicted by chance (G(cj) = 5'64, p > o-io). On the other hand, the distribution of maternal speech/infant response sequences when the mother made more than two utterances before the infant's response (Table 3) deviated highly significantly from that predicted by chance (G(9) = 239-5, p < O'ooi). Rising F o contours in maternal speech were likely to be responded to by the infant with vocalizations with rising F o contours more often than expected. Other types of F o contours seldom occurred. Similarly, each of the other three types of F o contours was followed by an infant vocalization of the same contour type more frequently than expected.
DISCUSSION
In a recent study that examined speech samples from eight British female adults addressing young children, Shute & Wheldall (1989) found that the degree of exaggeration in vocal pitch varied considerably across speakers. In addition to such inter-individual variability, the results of the present study reveal the presence of intra-individual variability: the pattern of vocal interaction between a caregiver and prelinguistic infant is context-sensitive and varies flexibly. While Shute & Wheldall suppose that the variability they found would reflect differences between the speakers regarding their attitude towards adult-child interactions, the six Japanese mothers studied here were likely to resort to maternal speech with exaggerated pitch patterns in cases where their infants were initially unresponsive. The attention-getting function of motherese is confirmed by the fact that these pitch modifications come into play when the mothers are having to make an effort to elicit responses from their infants. Moreover, when the infants were responding to maternal speech which had exaggerated pitch patterns, they tended to mimic those patterns, although they tended not to do so in response to maternal speech with nonexaggerated F o patterns. Regarding the bioacoustic bases of F o contours, an explanation was provided by Kent & Murray (1982). A falling F o contour may be the result of a decrease of subglottal air pressure towards the end of an infant's vocalization, with a concomitant reduction in vocal fold length and tension. For a rising F o contour to occur, an increase at the end of the vocalization in subglottal air pressure or vocal fold tension would need to occur. The different or, perhaps, purposeful laryngeal articulation required 220
JAPANESE MOTHERESE
for a rising F o contour is consistent with Cruttenden's (1981) suggestion that infants may actually learn the special use of rising F o contours. In previous acoustic research (Locke, 1983; Robb, Saxon & Grand, 1989), the infants were not considered to display an obvious contrastive use of different types of F o contour prior to o;6. Only Kessen, Levine & Wendrich (1979) report that younger infants are able to imitate the pitch of sounds they hear. Recently, however, there has been a growing literature suggesting continuities between prelinguistic and linguistic behaviours in normal infant vocal development (Koopmans-Van Beinum & Van Der Stelt, 1986; Kent & Hodge, 1989; Mitchell & Kent, 1990). Skilled vocal movement is gradually acquired by infants even in the prelinguistic period, at first in cooing and then in babbling. The importance of motor learning for early vocal development could be greater than has traditionally been assumed. The present study strongly suggests that a very early milestone could be the purposeful mimicking of the F o contour of maternal speech. Possibly by the age of o; 3-014, speech-motor control develops in infants, associated with the tongue, mouth, jaw and respiratory patterns, to produce vocalizations with distinctively different types of F o contour that were initially the result of the infant's 'accidental' opening and closing of the mouth while phonating. As suggested by many researchers, the salience of motherese for the infant apparently results in part from perceptual predispositions to attend to and process certain sounds more readily and effectively than others. A recent study (Cooper & Aslin, 1990) shows that infants' preference for exaggerated prosodic features is present from birth and may not depend on any specific postnatal experience. However, the salience also results from the infant's selective affective responsiveness to certain attributes of auditory signals (Fernald, 1984). As Halliday (1975) proposed, infants are 'learning how to mean' in the first year of life. They gradually become capable of expressing a huge variety of meanings, at first through the use of intonation contours, used consistently in particular functional contexts. The primary affective character of heard speech is accessible to the infants through the intonation contours of adult speech, and the early responsiveness to intonation contours provides a basis for the infants' later responsiveness to segments and words. By presenting exaggerated contours, maternal speech may help infants modify their own vocal responses. Piaget (1951) and Tomkins (1962) suggested that vocal imitation might develop through a process of 'contagion', which has an emotional basis. The prosodic patterns of motherese are more informative than A—A intonation and provide the infant with more reliable clues to the communicative intent of the speaker (Fernald, 1989). When the six Japanese mothers studied here resorted to utterances with exaggerated F o patterns, after repeated unsuccessful attempts to elicit vocal responses from their infants, the underlying communicative intent of the mothers to enter a joint affiliative interaction would surely have been obvious 221
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to the infants. Motherese in such circumstances appears to be an efficient way of providing the infants with opportunities for vocal practice.
REFERENCES Cooper, R. P. & Aslin, R. N. (1990). Preference for infant-directed speech in the first month after birth. Child Development 61, 1584-95. Cruttenden, A. (1981). Falls and rises: meanings and universals. Journal of Linguistics 17, 77-91. Fernald, A. (1984). The perceptual and affective salience of mother's speech to infants. In L. Feagans, C. Garvey & R. Golinkoff (eds), The origins and growth of communication. Norwood: Ablex. (1985). Four-month-old infants prefer to listen to motherese. Infant Behavior and Development 8, 181-95. (1989). Intonation and communicative intent in mother's speech to infants: is the melody the message? Child Development 60, 1497-510. Fernald, A. & Simon, T. (1984). Expanded intonation contours in mothers' speech to newborns. Developmental Psychology 20, 104-13. Fernald, A., Taeschner, T., Dunn, J., Papousek, M., Boysson-Bardies, B. de & Fukui, I. (1989). A cross-linguistic study of prosodic modifications in mothers' and fathers' speech
to preverbal infants. Journal of Child Language 16, 477-501. Garnica, O. (1977). Some prosodic and paralinguistic features of speech to young children. In C. E. Snow & C. A. Ferguson (eds), Talking to children: language input and acquisition. Cambridge: C.U.P. Grieser, D. L. & Kuhl, P. (1988). Maternal speech to infants in a tonal language: support for universal prosodic features in motherese. Developmental Psychology 24, 14-20. Halliday, M. A. K. (1975). Learning how to mean : explorations in the development of language. London: Edward Arnold. Kent, R. & Hodge, M. (1989). Oral-verbal morphogenesis: continuity and process in early speech behavior. Paper presented at the Symposium on Research in Child Language Disorders, University of Wisconsin-Madison. Kent, R. D. & Murray, A. D. (1982). Acoustic features of infant vocalic utterances at 3, 6 and 9 months. Journal of the Acoustical Society of America 72, 353-65. Kessen, W., Levine, J & Wendrich, K. A. (1979). The imitation of pitch in infants. Infant Behavior and Development 2, 93-9. Koopmans-van Beinum, F. & van der Stelt, J. (1986). Early stages in the development of speech movements. In B. Lindblom & R. Zetterstrom (eds), Precursors of early speech. New York: Stockton Press. Locke, J. L. (1983). Phonological acquisition and change. New York: Academic Press. Mitchell, P. R. & Kent, R. D. (1990). Phonetic variation in multisyllable babbling. Journal of Child Language 17, 247-65. Newport, E. L., Gleitman, H. & Gleitman, L. R. (1977). Mother, I'd rather do it myself: some effects and non-effects of maternal speech style. In C. E. Snow & C. A. Ferguson (eds), Talking to children : language input and acquisition. Cambridge: C.U.P. Papousek, M., Papousek, H. & Bornstein, M. (1985). The naturalistic vocal environment of young infants: on the significance of homogeneity and variability in parental speech. In T. M. Field & N. A. Fox (eds), Social perception in infants, Norwood: Ablex. Piaget, J. (1951). Play, dreams and imitation in childhood. New York: Norton. Robb, M. P., Saxon, J. H. & Grand, A. A. (1989). Vocal fundamental frequency characteristics during the first two years of life. Journal of the Acoustical Society of America 85, 1708-17. Shute, B. & Wheldall, K. (1989). Pitch alternations in British motherese: some preliminary acoustic data. Journal of Child Language 16, 503-12. Sokal, R. R. & Rohlf, F. J. (1981). Biometry (2nd edition). New York: Freeman. 222
JAPANESE MOTHERESE Stern, D. N., Spieker, S., Barnett, R. K. & MacKain, K. (1983). The prosody of maternal speech: infant age and context related changes. Journal of Child Language 10, 1-15. Stern, D. N., Spieker, S. & MacKain, K. (1982). Intonation contours as signals in maternal speech to prelinguistic infants. Developmental Psychology 18, 727-35. Tomkins, S. (1962). Affect, imagery, consciousness. Vol. 1. The positive affect. New York: Springer. Werker, J. F. & McLeod, P. J. (1989). Infant preference for both male and female infantdirected talk: a developmental study of attentional and affective responsiveness. Canadian Journal of Psychology 43, 230—46.
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Pitch characteristics of Japanese maternal speech to infants Nobuo Masataka Journal of Child Language / Volume 19 / Issue 02 / June 1992, pp 213 - 223 DOI: 10.1017/S0305000900011399, Published online: 17 February 2009
Link to this article: http://journals.cambridge.org/abstract_S0305000900011399 How to cite this article: Nobuo Masataka (1992). Pitch characteristics of Japanese maternal speech to infants. Journal of Child Language, 19, pp 213-223 doi:10.1017/ S0305000900011399 Request Permissions : Click here
Downloaded from http://journals.cambridge.org/JCL, IP address: 138.251.14.35 on 17 May 2015
. Child Lang. 19 (1992), 213-223. Printed in Great Britain
Pitch characteristics of Japanese maternal speech to infants* NOBUO MASATAKA The University of Tokyo (Received 25 June 1990. Revised 12 April 1991)
ABSTRACT
The fundamental frequency F o patterns of maternal speech addressed to infants aged 053-0; 4 were measured quantitatively. Speech samples were recorded when six Japanese-speaking mothers addressed an adult and their own infants. Japanese mothers speaking to adults use a relatively restricted F o range, concentrated around the mother's F o , which tends to be near the low end of the total range used. These acoustic characteristics are not altered substantially when these same women speak to their infants in initial utterances to attract the infants' attention. If such attempts are unsuccessful, however, they are likely to make more exaggerated utterances, in which F o shifts upward and the frequency range is significantly increased. Moreover, only when acoustic characteristics of maternal speech to infants are exaggerated, can the type of F o contour of the infant's subsequent response be predicted to a significant extent from the mother's preceding utterance.
INTRODUCTION
There is a growing literature on paralinguistic or prosodic features of parental speech to infants (Garnica, 1977; Newport, Gleitman & Gleitman, 1977; Papousek, Papousek & Bornstein, 1985). The studies report that adult speech to infants is characterized by a higher overall pitch, wider pitch excursions, more distinctive pitch contours, slower tempo and longer pauses than in normal adult conversation. Cross-linguistic research has documented common patterns of such exaggerated features in parental speech to infants younger than age o;8 across a number of European languages and Japanese (Fernald, Taeschner, Dunn, Papousek, Boysson-Bardies & Fukui, 1989) and in maternal speech in Mandarin Chinese (Grieser & Kuhl, 1988). These [•] I thank Shozo Kojima and Toshikazu Hasegawa for their help in conducting this research. I am grateful to Katharine Perera and two anonymous reviewers for making invaluable comments. Address for correspondence: Nobuo Masataka, Department of Anthropology, Faculty of Science, The University of Tokyo, Hongo, Bunkyo, Tokyo 113, Japan. 213 9
JCL19
CHILD LANGUAGE
features are thought to serve several functions related to language development. In particular the use of exaggerated acoustic characteristics in the early preverbal period has been assumed to function primarily to engage the infant's attention and maintain social interaction. Using a conditioned headturning procedure, Fernald (1985) showed that infants aged o;4 turned their heads more often towards a recording of female infant-directed speech than female adult-directed speech. Werker & McLeod (1989) measured the amount of time infants aged 0:4-0; 5 and infants aged 017-059 viewed a television monitor^ that presented either a female or a male actor speaking infant-directed or adult-directed speech. They found that both groups of infants watched the monitor longer when infant-directed speech was being presented. In this paper, further evidence is presented for the attention-getting properties of infant-directed intonation. It is well-known that for a-child to engage in joint action with a parent, considerable interactional support by the parent is necessary, especially in the beginning phases of joint action. Parents have to repeat their attempts to elicit vocal responses from infants as long as the infants remain unresponsive. This study undertook acoustical analyses on sequences of utterances as mothers attempted to get vocal behaviour from their infants. The analysis concentrated on fundamental frequency (Fo) patterns. The results reveal that mothers apparently alter the pitch charac. teristics of their speech in sequences of repeated utterances addressed to their infants. I also examined whether the change in maternal pitch could differentially affect acoustic features of pitch in immediately subsequent infant utterances. In terms of F o contours, I examined how well the type of subsequent infant vocalizations could be predicted from the type of immediately preceding maternal speech, using G-tests of goodness of fit (Sokal & Rohlf, 1981). METHOD
Subjects The subjects were six monolingual women who spoke only Japanese. All of the women were full-time housewives between the ages of 24 and 29. Each subject was the mother of a firstborn male infant aged o 13-0 54. The infants were healthy and had uncomplicated prenatal and perinatal histories. Procedure Each mother was recorded in her home as she spoke to her infant and as she telephoned a Japanese-speaking friend. Studies have shown that there are no significant differences between the prosodic features of maternal speech samples collected at home as opposed to in a laboratory setting (Stern, Spieker, Barnett & MacKain, 1983). Recordings were made with the mother 214
JAPANESE MOTHERESE
seated in a chair next to a studio-quality portable tape recorder (Sony TCD5M). The mother and the infant each wore a high quality lapel microphone (Sony ECM16). Inputs from the microphone were mixed and recorded on one channel of the tape recorder. The order of the listener conditions was counterbalanced across subjects. Mothers were told that their speech in different settings was of interest, but not specifically that characteristics related to its F o features would be analysed. Adult-to-Adult (A-A) speech. When adults speak to other adults, the speech of the two speakers tends to overlap, obscuring the acoustic features of interest. Recordings made while the speaker is talking to someone over the telephone eliminate this problem because the second speaker is not recorded. Comparison recordings were made in which the mother spoke with a native speaker in person or over the telephone; these tapes verified that equally typical speech could be sampled under both recording procedures. The mother prearranged to telephone a friend during our visit. Each mother was left alone in the room during the telephone conversation and was recorded for 15 minutes. Adult-to-Infant (A—I) speech. Each mother held her infant on her lap as she sat in the chair. The observer instructed the mother to talk to her infant as she normally might when they were alone together. The mother and infant were left alone in the room for the duration of the recording and were recorded for 15 minutes in a given recording session. For each mother-infant dyad, a total of three sessions was undertaken. In each session, episodes of interaction were identified; episodes being defined as series of rounds with a focus on a specific topic, set off by periods of verbal inactivity. Episodes were ultimately constrained by the infant's attention. Episodes began with the mother attempting to attract her infant's attention through speech. As a unit for acoustic measurements, an utterance was operationally defined as a continuous vocalization of a mother or an infant bounded by pauses of longer than 0-3 sec. Thus two complete run-on sentences by a mother without an intervening pause were scored as an utterance. All meaningful communicative vocalizations were considered as words, e.g. ooh, aah and hmm. Non-verbal sounds (kisses, laughter) and routines (songs, nursery rhymes) were excluded. If an infant vocalized within 3-0 sec of an utterance by its mother, that was counted as an infant response and the mother's utterance was the beginning of an episode. The mother's utterance in each such episode was defined as an 'initial maternal utterance'. If the mother was unsuccessful, she made only a few utterances, punctuated by silence on the infant's part. Even when she was successful, she frequently had to make more than one utterance before the infant responded. Once the infant responded, the mother would continue the vocal interactions as long as the infant remained attentive and responsive. When the infant turned his attention elsewhere, the episode would end. The mother 215 9-2
CHILD LANGUAGE
would then wait several minutes before initiating a new episode. For analysis of speech features, only the initial maternal utterance and the initial vocal response of the infant to that utterance in each A-I episode were used. The number of utterances the mother required to initiate the episode was also counted. Acoustic measurements (1) Fo measures Analysis of F o was performed on all utterances recorded in A-A speech and all initial maternal utterances (defined above) in A-I speech for each subject, using a Kay DSP Sonagraph (Model 5500—1) with 150 Hz band filter and frequency scale up to 4000 Hz, connected to a PDP 11/23 computer. The sonagraph was set to measure F o value (with accuracy of + 1 Hz) for each 20 msec of voiced speech by means of Fast Fourier Transformation. The information obtained was stored in the PDP computer, which calculated average F o (the mean of the distribution of values for each utterance) and F o range (maximum minus minimum values for each utterance). (2) F o contour classification Previous studies have noted that the intonation contour typical of infant-directed speech can be classified according to the extent and direction of the frequency excursion (Stern, Spieker & MacKain, 1982; Stern, Spieker, Barnett & MacKain, 1983; Fernald & Simon, 1984; Grieser & Kuhl, 1988). In this study, therefore, I performed F o contour classification on all initial maternal utterances in A-I speech and infant's initial responses to them, using five categories of F 0 -contour type: RISING, FALLING, FLAT, BELL-SHAPED, and COMPLEX. In order to classify contour types, sonagrams produced were visually inspected. All of the contours were categorized as one of the five 'prototypical patterns'. Altogether, four raters coded the utterances: two of them coded the mothers' vocalizations and the other two coded the infant vocalizations. None of them was informed of the purpose of the present study. Inter-rater reliability, defined as the percentage of instances for which there was agreement on the classification of contour type, was greater than 90%. For cases in which there was disagreement, the two judges re-examined the contours together and decided how they should be classified. Rising and falling contours were often marked by only relatively small upward and downward frequency shifts, respectively. However, a pitch rise or fall was recognized only when the value of a frequency-modulation range of a continuous slope exceeded 15 Hz in maternal vocalizations, and 10 Hz in infant vocalizations, which are narrower in range.
216
JAPANESE MOTHERESE
(a)
Adult-to-infant speech
200-
Adult-to-adult speech
i
I
I
I
I
(b) Adult-to-infant speech 50Adult-to-adult speech
1 2 3 4 ^ 5 No. of maternal utterances before infant response Fig. i. Average pitch (a) and pitch range (b) for initial maternal utterances in A-I speech. (Average values of the mothers' utterances in A-A speech are given by the horizontal straight lines.) RESULTS
FQ measures
Figure i presents the average F o and F o range for all the subjects' utterances in A-A speech and all initial maternal utterances in A-I speech. For A-I speech the data are presented in terms of the number of utterances the mother made before successful elicitation of the infant's response in each episode (represented on the abscissa of Fig. i). Detailed individual data are shown in Table i. Comparisons of the average F o for A-A speech and A-I speech showed that, overall, the mothers' average F o in the A-I condition exceeded that observed in the A-A condition. Examining the F o values between the two conditions, a single classification ANOVA showed that there was a significant difference, F(i, 5) = i8 - 4i, p < o-oi. However, follow-up t tests revealed that each subject demonstrated a significant increase in her F o values only when she made more than two utterances before elicitation of the infant's response (/> < o - oi, in all cases). When the first one or two utterances by the mother were responded to by the infant, the F o did not differ significantly from that observed in the A-A condition (p > o-io, in all cases). 217
CHILD LANGUAGE
i. Mean values of average Fo and Fo range in individual subjects' utterances in the A-A and A-I conditions {with s.D. in brackets)
TABLE
A—I condition
Number of maternal utterances before infant response Parameter/ Subject No.
A-A condition
i
2
3
4
I75(i7)
181 (20)
234(19)
236(25)
252 (28)
177(15)
2
199(20)
3 4 5 6
212 (23)
216(18) 208(15) 206 (23) 213(30) 206 (29)
272 (28) 235 (22) 255(48) 240 (22) 226(10)
288(30) 296 (23) 260 (43) 273 (27) 254(35)
202 (26) 195 (10) 189(16) 196(18)
Average Fo (Hz)
F o range (Hz) 2
3 4
5 6
20 (4-2)
26 (6-s)
71 (224)
245 (26) 243 (18) 289(52) 266(31) 257('7) 77 (160)
75 (>93)
18 (27)
i9(3-3) 23 (6-4)
30 (7-o) 25 (3-6) 24 (2-7) 26 (20) 20(1-9)
83 (287) 55 (32-2) 67 (200) 66(145) 51 (126)
75 (205) 98 (250) 92 (25-8) 104(28-9) 80 (16-6) i°7 (365) 78 (223) 86 (342) 71 (180) 88 (235)
23 (4'5) 31 (60)
203 (16) 187(15) 208(19)
28(31) 17(1-6) 18 ( 2 2 )
193(23)
24 (38) 16 (1-2)
22 (37)
Similar results were obtained from the analysis of the F o range for A-A speech and A-I speech. An ANOVA revealed that there was a significant difference in the F o range values between the A-A condition and the A-I condition, F ( i , 5) = 19-25,/) < o-oi. Overall, the F o range for the six subjects in the A-I condition exceeded that observed in the A-A condition. Again, follow-up t tests revealed that each subject demonstrated a significant increase in her F o range values only when she made more than two utterances before the infant's response (p < o-oi, in all cases). When only one or two utterances were made by the mother before the response, the F o range values did not differ significantly from that observed in the A-A condition (J> > o-io, in all cases). F o contour classification The results described above indicate that acoustic characteristics which have been reported to be typical of motherese are also displayed by the subjects in the present study. Does exaggerated maternal speech elicit an infant's response in a different manner from that in which less exaggerated speech does ? In order to examine this, the following analysis was undertaken. I hypothesized that the F o contour of exaggerated maternal speech could significantly affect the F o contour of immediately subsequent infant vocalizations, but that the F o of less exaggerated speech would not be able to do so. Therefore, the following analyses were conducted independently on two 218
JAPANESE MOTHERESE
2. Distribution of maternal speech/infant's response sequences when the mother made only one or two utterances before infant's response
TABLE
Contour type of subsequent infant 's response initial maternal utterance Rising (AT = 2 5 1 )
Falling (AT = 2 8 1 )
Bell-shaped (iV=i 47 )
Flat or Complex (N= 166) Total N
Rising
Falling
Bell-shaped
Flat or Complex
72
88 (9i-5)
4> (425)
(49-0)
50
(680) 77 (762) 37
102
51
51
(102-4) 63
(476)
(549)
22
25
(39-8)
(53-6)
(24-9)
(287) 39 (32-4)
43
55
(4S'O)
(6o-5)
229
308
29
(280) 143
165
G(9) = 564, p > o-io. Expected values calculated from marginal totals are given in parentheses.
3. Distribution of maternal speech/infant's response sequences when the mother made more than two utterances before infant's response
TABLE
Contour type of subsequent infant 's response initial maternal utterance Rising
Rising 114
Falling 73
(786)
Bell-shaped
Flat or Complex
23
9 (269) 8 (23-2) 7
(AT = 219)
(691)
Falling (AT =189) Bell-shaped
44
109
28
(597)
(675)
(38-3)
29
(AT = 1 0 7 )
(33-8)
55 (217)
Flat or Complex (AT=
Total N
112)
16
(384)
(44-4)
24
14
21
(35-4)
(402)
(22-7)
198
225
127
(3i-0 53 (13-8) 77
G(9) = 239-5, p < o o o i . Expected values calculated from marginal totals are given in parentheses.
different subsets of the data, classified according to the following criteria. (1) when the mother made only one or two utterances before her infant responded (N = 845); (2) when the mother made more than two utterances before her infant responded (N = 627). All contours occurring in the maternal and infant utterances were classified according to the five contour types described above. In all, rising contours accounted for 32 % in maternal speech and for 29% in infant speech, and falling contours for 32% in maternal speech and for 36% in infant speech. Bell-shaped contours containing both a rise and a fall accounted for 17% of the data in maternal 219
CHILD LANGUAGE
speech and for 18 % of the data in infant speech. The remaining two contour types, complex and flat, only occurred less than 10% of the time in both maternal and infant speech. Those latter two types have therefore been combined in Tables 2 and 3. Table 2 presents the distribution of maternal speech/infant response sequences when the mother made only one or two utterances before the infant's response. The distribution did not deviate significantly from that predicted by chance (G(cj) = 5'64, p > o-io). On the other hand, the distribution of maternal speech/infant response sequences when the mother made more than two utterances before the infant's response (Table 3) deviated highly significantly from that predicted by chance (G(9) = 239-5, p < O'ooi). Rising F o contours in maternal speech were likely to be responded to by the infant with vocalizations with rising F o contours more often than expected. Other types of F o contours seldom occurred. Similarly, each of the other three types of F o contours was followed by an infant vocalization of the same contour type more frequently than expected.
DISCUSSION
In a recent study that examined speech samples from eight British female adults addressing young children, Shute & Wheldall (1989) found that the degree of exaggeration in vocal pitch varied considerably across speakers. In addition to such inter-individual variability, the results of the present study reveal the presence of intra-individual variability: the pattern of vocal interaction between a caregiver and prelinguistic infant is context-sensitive and varies flexibly. While Shute & Wheldall suppose that the variability they found would reflect differences between the speakers regarding their attitude towards adult-child interactions, the six Japanese mothers studied here were likely to resort to maternal speech with exaggerated pitch patterns in cases where their infants were initially unresponsive. The attention-getting function of motherese is confirmed by the fact that these pitch modifications come into play when the mothers are having to make an effort to elicit responses from their infants. Moreover, when the infants were responding to maternal speech which had exaggerated pitch patterns, they tended to mimic those patterns, although they tended not to do so in response to maternal speech with nonexaggerated F o patterns. Regarding the bioacoustic bases of F o contours, an explanation was provided by Kent & Murray (1982). A falling F o contour may be the result of a decrease of subglottal air pressure towards the end of an infant's vocalization, with a concomitant reduction in vocal fold length and tension. For a rising F o contour to occur, an increase at the end of the vocalization in subglottal air pressure or vocal fold tension would need to occur. The different or, perhaps, purposeful laryngeal articulation required 220
JAPANESE MOTHERESE
for a rising F o contour is consistent with Cruttenden's (1981) suggestion that infants may actually learn the special use of rising F o contours. In previous acoustic research (Locke, 1983; Robb, Saxon & Grand, 1989), the infants were not considered to display an obvious contrastive use of different types of F o contour prior to o;6. Only Kessen, Levine & Wendrich (1979) report that younger infants are able to imitate the pitch of sounds they hear. Recently, however, there has been a growing literature suggesting continuities between prelinguistic and linguistic behaviours in normal infant vocal development (Koopmans-Van Beinum & Van Der Stelt, 1986; Kent & Hodge, 1989; Mitchell & Kent, 1990). Skilled vocal movement is gradually acquired by infants even in the prelinguistic period, at first in cooing and then in babbling. The importance of motor learning for early vocal development could be greater than has traditionally been assumed. The present study strongly suggests that a very early milestone could be the purposeful mimicking of the F o contour of maternal speech. Possibly by the age of o; 3-014, speech-motor control develops in infants, associated with the tongue, mouth, jaw and respiratory patterns, to produce vocalizations with distinctively different types of F o contour that were initially the result of the infant's 'accidental' opening and closing of the mouth while phonating. As suggested by many researchers, the salience of motherese for the infant apparently results in part from perceptual predispositions to attend to and process certain sounds more readily and effectively than others. A recent study (Cooper & Aslin, 1990) shows that infants' preference for exaggerated prosodic features is present from birth and may not depend on any specific postnatal experience. However, the salience also results from the infant's selective affective responsiveness to certain attributes of auditory signals (Fernald, 1984). As Halliday (1975) proposed, infants are 'learning how to mean' in the first year of life. They gradually become capable of expressing a huge variety of meanings, at first through the use of intonation contours, used consistently in particular functional contexts. The primary affective character of heard speech is accessible to the infants through the intonation contours of adult speech, and the early responsiveness to intonation contours provides a basis for the infants' later responsiveness to segments and words. By presenting exaggerated contours, maternal speech may help infants modify their own vocal responses. Piaget (1951) and Tomkins (1962) suggested that vocal imitation might develop through a process of 'contagion', which has an emotional basis. The prosodic patterns of motherese are more informative than A—A intonation and provide the infant with more reliable clues to the communicative intent of the speaker (Fernald, 1989). When the six Japanese mothers studied here resorted to utterances with exaggerated F o patterns, after repeated unsuccessful attempts to elicit vocal responses from their infants, the underlying communicative intent of the mothers to enter a joint affiliative interaction would surely have been obvious 221
CHILD LANGUAGE
to the infants. Motherese in such circumstances appears to be an efficient way of providing the infants with opportunities for vocal practice.
REFERENCES Cooper, R. P. & Aslin, R. N. (1990). Preference for infant-directed speech in the first month after birth. Child Development 61, 1584-95. Cruttenden, A. (1981). Falls and rises: meanings and universals. Journal of Linguistics 17, 77-91. Fernald, A. (1984). The perceptual and affective salience of mother's speech to infants. In L. Feagans, C. Garvey & R. Golinkoff (eds), The origins and growth of communication. Norwood: Ablex. (1985). Four-month-old infants prefer to listen to motherese. Infant Behavior and Development 8, 181-95. (1989). Intonation and communicative intent in mother's speech to infants: is the melody the message? Child Development 60, 1497-510. Fernald, A. & Simon, T. (1984). Expanded intonation contours in mothers' speech to newborns. Developmental Psychology 20, 104-13. Fernald, A., Taeschner, T., Dunn, J., Papousek, M., Boysson-Bardies, B. de & Fukui, I. (1989). A cross-linguistic study of prosodic modifications in mothers' and fathers' speech
to preverbal infants. Journal of Child Language 16, 477-501. Garnica, O. (1977). Some prosodic and paralinguistic features of speech to young children. In C. E. Snow & C. A. Ferguson (eds), Talking to children: language input and acquisition. Cambridge: C.U.P. Grieser, D. L. & Kuhl, P. (1988). Maternal speech to infants in a tonal language: support for universal prosodic features in motherese. Developmental Psychology 24, 14-20. Halliday, M. A. K. (1975). Learning how to mean : explorations in the development of language. London: Edward Arnold. Kent, R. & Hodge, M. (1989). Oral-verbal morphogenesis: continuity and process in early speech behavior. Paper presented at the Symposium on Research in Child Language Disorders, University of Wisconsin-Madison. Kent, R. D. & Murray, A. D. (1982). Acoustic features of infant vocalic utterances at 3, 6 and 9 months. Journal of the Acoustical Society of America 72, 353-65. Kessen, W., Levine, J & Wendrich, K. A. (1979). The imitation of pitch in infants. Infant Behavior and Development 2, 93-9. Koopmans-van Beinum, F. & van der Stelt, J. (1986). Early stages in the development of speech movements. In B. Lindblom & R. Zetterstrom (eds), Precursors of early speech. New York: Stockton Press. Locke, J. L. (1983). Phonological acquisition and change. New York: Academic Press. Mitchell, P. R. & Kent, R. D. (1990). Phonetic variation in multisyllable babbling. Journal of Child Language 17, 247-65. Newport, E. L., Gleitman, H. & Gleitman, L. R. (1977). Mother, I'd rather do it myself: some effects and non-effects of maternal speech style. In C. E. Snow & C. A. Ferguson (eds), Talking to children : language input and acquisition. Cambridge: C.U.P. Papousek, M., Papousek, H. & Bornstein, M. (1985). The naturalistic vocal environment of young infants: on the significance of homogeneity and variability in parental speech. In T. M. Field & N. A. Fox (eds), Social perception in infants, Norwood: Ablex. Piaget, J. (1951). Play, dreams and imitation in childhood. New York: Norton. Robb, M. P., Saxon, J. H. & Grand, A. A. (1989). Vocal fundamental frequency characteristics during the first two years of life. Journal of the Acoustical Society of America 85, 1708-17. Shute, B. & Wheldall, K. (1989). Pitch alternations in British motherese: some preliminary acoustic data. Journal of Child Language 16, 503-12. Sokal, R. R. & Rohlf, F. J. (1981). Biometry (2nd edition). New York: Freeman. 222
JAPANESE MOTHERESE Stern, D. N., Spieker, S., Barnett, R. K. & MacKain, K. (1983). The prosody of maternal speech: infant age and context related changes. Journal of Child Language 10, 1-15. Stern, D. N., Spieker, S. & MacKain, K. (1982). Intonation contours as signals in maternal speech to prelinguistic infants. Developmental Psychology 18, 727-35. Tomkins, S. (1962). Affect, imagery, consciousness. Vol. 1. The positive affect. New York: Springer. Werker, J. F. & McLeod, P. J. (1989). Infant preference for both male and female infantdirected talk: a developmental study of attentional and affective responsiveness. Canadian Journal of Psychology 43, 230—46.
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