language development. When adults address infants and young children, they ... nald et al., 1989), as well as in maternal speech in Mandarin Chinese ( ..... the particular patterned input of phonetic and syllabic units, that is, the .... A dictionary.
INFANT
BEHAVIOR
AND
DEVELOPMENT
Motherese
15,
453-460
(1992)
in a Signed NOBUO
language
MASATAKA
The University
of Tokyo
It is well known that when they oddress their infants, mothers substontiolly olter the acoustic characteristics of their speech. In this experiment, the possibility was explored thot o similor phenomenon might occur in a signed language. Eight deof mothers, each of whom used Joponese Sign Language as o first language, were observed when interacting with their deaf infants and when interacting with their deaf odult friends. When communicating with their infonts, the mothers used signs at o significantly slower tempo thon when communicating with their friends. They tended to repeat the some sign frequently, ond the movements associated with each sign were somewhot exaggerated. Thus, a phenomenon quite anologous to motherese in moternol speech wos identified. The possible functional significance of this phenomenon is discussed.
motherese
signed
languoge
maternol
speech
language
development
When adults address infants and young children, they tend to modify their speech in distinctive ways. The linguistic features of this modified speech, mofherese, include fewer words per utterance, more repetitions and expansion, better articulation, and decreased structural complexity (Ferguson, 1964; Ratner & Pye, 1984; Snow, 1977). Prosodic modifications include higher overall pitch, wider pitch excursions, more distinctive pitch contours, slower tempo, longer pauses, and increased emphatic stress (Garnica, 1977; Masataka, 1992; Newport, Gleitman, & Gleitman, 1977; Papousek, Papousek, & Bornstein, 1985). Interest in the structure and function of motherese stems from the possibility that such speech may facilitate language development in the young child. Cross-linguistic research has documented common patterns of such distinctive features in parental speech directed towards infants across a number of European languages and Japanese (Fernald et al., 1989), as well as in maternal speech in Mandarin Chinese (Grieser & Kuhl, 1988). The various earlier studies suggest that motherese may have universal linguistic and prosodic features. Such features are assumed to serve three functions, all of which are related to language development. First, the
I am grateful to Tomoko Fukui and Keika Kawashima far their assistance with the collection of data, and all the families who participated in this study far their collaboration. I am also greatly indebted to Elizabeth Bates and to an anonymous reviewer for reading an earlier draft of this article and far making a number of invaluable comments. Correspondence and requests for reprints should be sent to Nobua Masataka, Department of Anthropology, Faculty of Science, The University of Tokyo, Hongo, Bunkyo, Tokyo 113, Japan.
453
454
MASATAKA
enhanced acoustic features of motherese may differentially elicit and, perhaps, maintain the infant’s attention. Experimental studies have indicated that infants are more likely to pay attention to infant-directed speech than to adult-directed speech (Fernald, 1985). Second, a possible affective role of motherese has been reported: 4- to 5-month-old and 7- to 9-month-old infants who watched videotapes of a female talking to an infant or talking to an adult demonstrated more positive affect while watching the infant-directed tape. Furthermore, the magnitude of this effect was greater in the case of younger infants (Werker & McLeod, 1989). These results indicate that infants find infant-directed speech less affectively ambiguous than adult-directed speech. Finally, a potential linguistic benefit of motherese may exist. For instance, such speech facilitates the infant’s detection of, and discrimination between, major linguistic boundaries. Certain characteristics of motherese make these boundaries more noticeable, thereby “instructing” infants about language (Karzon, 1985). In this experiment, the possibility was explored that the phenomenon of motherese might extend to a naturally evolved human signed language. Signed languages are organized in an identical fashion to spoken languages with regard to phonology, morphology, syntax, and semantics (Klima & Bellugi, 1979). When adults produce manual activities that are part of the phonetic inventory of signed languages in communicating with young deaf children, who have only rudimentary knowledge of language, one would predict that the social interaction should have as unusual a quality as when adults speak to young hearing children. That is, if the interaction is to be established and maintained, adults must be led to utilize special constraints in their activities and to produce signals, in either the signed or spoken modalities, in a somewhat modified manner according to the infant’s level of attention and comprehension. In this experiment, eight deaf Japanese mothers were observed while interacting with their own deaf infants and while interacting with their adult deaf friends. As a first step, quantitative comparisons were made of tempo, the degree of repetition, and the exaggeration of movements of displayed signs during interactions between mothers and their infants and their adult friends. METHOD Subjects
The subjects were eight deaf women who had acquired Japanese Sign Language (Shinoda, 1985) as a first language. All of the women were full-time homemakers between the ages of 26 and 33 years, and their husbands were also deaf. Each subject was the mother of a firstborn, profoundly deaf infant who was between 8 and 11 months of age at the time of the experiment. Subjects were contacted by an advertisement in a local newspaper.
MOTHERESE
IN A SIGNED
LANGUAGE
455
Procedure
Each mother was filmed in a laboratory chamber (12.5 x 4.5 x 2.2 m) under two sets of conditions: during interactions with her infant and during interactions with an adult female, deaf friend who also used Japanese Sign Language as a first language. Recordings were made with each mother and her infant or friend seated in a chair in a face-to-face position. The height of each chair was adjusted such that the eyes of the mothers, their infants, and their friends were about 95 cm above floor level. The infant’s body was fastened to the seat by a seat belt. A distance between the chairs was 135 cm. The mother’s behavior was monitored with two movie cameras, and that of the infant or friend was monitored with a single camera. The framing rate for filming the mother was 50 frames per second. Each of the cameras was fixed on a tripod and fitted with a zoom lens. Two mirrors were hung on the roof of the chamber: one in front of the mother and the other in front of the infant or friend, both mirrors being 45” to the medial plane. One of the cameras was placed behind the mother at a distance of about 2.5 m, and one of the other two cameras was behind the infant or friend at the same distance. Each camera monitored the reflection from a mirror, which provided a plane view of the target individual. The third camera was placed on the right of the mother, 90” to the sagittal plane of the mother, at a distance of about 1 m. This camera provided a film of the right side of the mother. The position of the lens was adjusted to be approximately at the level of the mother’s elbow when she was seated and not engaged in any particular activity. The order of the two partner conditions was counterbalanced across subjects. Mothers were notified that their behavior in different settings was of interest, but they were not told specifically that signed language would be analyzed. At the beginning of each recording session, the mother was instructed to interact with her infant or friend as she normally might when they were alone together. She was told not to move her head during the session. Thereafter, the pair was left alone in the room for the duration of the recording and subjects were filmed for 15 min. None of the mothers was allowed to use toys or other instruments to get the attention of her infant. Analysis
The first minute of each 15-min period of recording in the two conditions for each subject was eliminated. Any meaningful sign recorded during the remaining 14 min was transcribed by two trained observers. The following analysis was performed by each of them separately and independently. They were not notified of the purpose of the experiment. If the mother repeated the same sign consecutively, the repetition was noted. For each sign, the duration was measured by counting the frames on which
MASATAKA
Figure recorded
1. Schematic representation on film. The points marked
of the plane by a light
view (A) and the pen on the digitizer
side are
view (B) of the mother indicated by an X.
OS
the sign was filmed. Moreover, for each of the frames recorded by the caGera located above the mother, the position of the right hand in relation to the head (angle subtended by the right hand with respect to the sagittal plane) was noted (Figure 1A). For a given sign, the mean value of this angle was estimated. For each of the frames recorded by the camera on the right of the mother, the position of the right elbow (angle subtended by the right elbow with respect to the vertical axis) was noted (Figure 1B). Values were averaged for each sign. For measuring the positions of the hand and the elbow, each of the frames was projected by a movie projector onto a digitizer, which was connected to a minicomputer (NEC PC-9801). By plotting the position of the hand and the head or the position of the elbow and the body axis on the digitizer with a light pen, the computer measured the angle between them with an accuracy of kO.5”. These measurements were performed to analyze the degree of exaggeration of signing by the mother. Whereas spoken languages are processed by hearing infants mainly in the auditory mode, signed languages are processed by deaf infants in the visual mode. Thus, it was hypothesized that exaggeration of signing behavior should appear in the pattern of movements of hands and arms that were making the signing gestures. However, such measurements are relevant only if related to the infant’s visual behavior. To monitor this behavior, for each of the frames filmed by the camera above the infant, the angle subtended from the center of the infant’s forehead to the sagittal
MOTHERESE
IN A SIGNED
LANGUAGE
457
plane was measured by the same procedure as that used for measurement of the position of the mother’s hand. Values were averaged for each sign by the mother and, for each mother-infant dyad, correlation coefficients were computed between averaged angles subtended by the infant’s forehead, and the mother’s hand and elbow. RESULTS Interobserver agreement in determining the occurrence of repetitions of signs and in measuring their duration and angle in relation to the sagittal plane and body axis was estimated by correlating the scores assigned by the two observers for each mother. The Pearson product-moment correlation coefficients were as follows: repetition rate, r = .99, p < .OOOl; duration, r = .97, p < .OOl; angle subtended by the mother’s right hand with respect to the sagittal plane, r = .97, p < .OOl; angle subtended by the mother’s right elbow with respect to the vertical axis, r = .96, p < .OOl; angle subtended from the infant’s forehead to the sagittal plane, I = .98, p < .OOl. Thus, in order to assign a value for each parameter for each mother, scores recorded by the two observers were averaged. Table 1 (p. 458) presents a summary of the results of the analysis. Comparison of the rates of repetition of signs for signs directed to her infant and for signs directed to her adult friend showed that the rates for the eight mothers when they interacted with their infants exceeded the rates when they interacted with their adult friends. A f test showed that each mother demonstrated a significant increase in repetitions when she interacted with her infant, f(7) = 23.31, p < .OOl. For analysis of the duration of signs, values were averaged across subjects for each condition. A two-way analysis of variance (ANOVA) showed that the duration was significantly longer in the case of signs directed to her infant than in the case of signs directed to her adult friend, F(1, 7) = 30.88, p < .OOl. Follow-up two-tailed Mann-Whitney U tests showed that for each subject there was a significant increase in the duration of signs (p < .Ol, in all cases). When the angle of the hand and elbow subtended to the sagittal plane or body axis was calculated across subjects for each condition, the same effect was apparent. Mean scores for maximum values of angles for each sign directed to infants exceeded those for signs directed to adults, F(1,7) = 18.76 for the hand, 12.90 for the elbow, p < .Ol. Similarly, mean scores of averaged values of angles for each sign directed to infants significantly exceeded those for signs directed to adults, F(1,7) = 16.55 for the hand, 13.04 for the elbow, p < .Ol. With regard to all these parameters, follow-up Mann-Whitney U tests revealed that each subject demonstrated a significant increase in these angles when she interacted with her infant (p < .05, in all cases).
Group
Subject
(Ml
Average
6.6
3.6 5.3
6.6 6.2 9.3
2.3 5.1
7.5 9.3 4.8
2.9
1.0 1.4 2.1
2.1 4.7 4.8
Adult
Infant
Rate 1%)
39.1
43.9 40.3
38.5 44.9 37.3
34.5 30.6 42.7
32.8
38.5 35.7
33.1 39.3 26.7
27.0 26.4 35.8
Adult
29.2
36.8
32.4
39.1 28.0 23.5
44.7 41.8 31.0
41.1
21.0 21.3 23.6
23.8
22.4
27.1 28.3 23.1
23.6
32.3 35.4 38.6
Infant
Average
by the Hand
17.9
17.3
20.5 18.2 17.9
18.5 16.2 14.6 19.8
Adult
21.3
19.4
19.2 24.6 17.5
20.2 22.4 21.3
26.1
Infant
Maximum
Angle
15.0
13.0
14.8 19.5 12.3
14.4 16.3 12.0
17.9
Adult
Subtended
to the Sogittol Plone, ond Angle Subtended With Their Infants ond With Adult Friends
Adult
Subtended
32.8
Maximum
Angle
TABLE 1 Hond With Respect Mothers Interacted
48.3 39.5 42.8 43.6
Infant
Subtended by the Axis for Signs When
(No. of Frames)
Angle Body
Infant
Duration
Rates, Durotion, With Respect to the
Repetition
Repetition
16.4
14.6
14.2 21.9 12.6
17.7 15.8 13.4
20.6
Infant
Average
by the Elbow
by the
11.5
9.3
10.4 15.6 8.9
12.1 11.7 9.7
14.3
Adult
Elbow
MOTHERESE
IN A SIGNED
LANGUAGE
459
For each sign, the average angle subtended by the infant’s forehead to the sagittal plane showed a significant positive correlation with the angle of the mother’s hand (r > .78, p< .OOl, in every mother-infant dyad) and with the angle of the mother’s elbow (r > .81, p < .OOl, in every mother-infant dyad). DISCUSSION Striking differences exist between the signed language used by Japanese deaf mothers when they interact with their infants and when they interact with their adult friends. When interacting with their infants, they use signs at a relatively slower tempo and are more likely to repeat the same sign, and movements used to make the signs are exaggerated. Observations of the infant’s visual behavior suggest that such exaggerated gestures may evoke more robust responses from the infant. The outcome of this experiment reveals a phenomenon that is analogous to motherese in maternal speech. Although the role played by the acoustic features of motherese in infant development is still unclear, it should be noted that infant-directed speech, with more repetitions and expansion, and at a slower tempo than normal adult conversation, does not appear frequently until the infant is approximately 7 months of age and is able to respond to adult speech differentially (Friedlander, 1968; Phillips, 1973; Snow, 1977). These features of motherese have emphasized the need to study their linguistic impact on infants. The timing of frequent use of such motherese has been interpreted as support for the notion that mothers adjust their speech to their infant’s linguistic level, and that no adjustment is, therefore, called for before the infant is old enough to process the syntactic form of the speech directed towards him or her. Recent studies indicate that infants are innately predisposed to discover the particular patterned input of phonetic and syllabic units, that is, the particular patterns in the input signal that correspond to the temporal and hierarchial grouping and rhythmical characteristics in natural spoken language phonology (Jusczyk, 1982; Mehler et al., 1988). Moreover, this predisposition is a property of an amodal language capacity (Petitto & Marentette, 1991). Patterned input in either the signed or spoken modalities with phonetic and syllabic organizations can serve as the vehicle for development of language. Thus, the production of motherese in the manual mode could help deaf infants identify visually the finite inventory of basic units, from which a signed language is constructed. When a particular patterned input is expressed as motherese, it appears to enhance infants’ acquisition of the basic forms of signed language. Continually monitoring the infants’ degree of attention and understanding, mothers modify various features of their signing so as to maintain the degree of the infants’ responsiveness at optimal level.
460
MASATAKA
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