Integrating Language and Gesture in Infancyinfancy is discussed in detail by Bates et al., (1983)....

Developmental Psychology Copyright 1989 by the American Psychological Association, t~e. 1989, Vol. 25, No. 6, 1004-1019 0012-1649/89/$00.75

Integrating Language and Gesture in Infancy

Elizabeth Bates and Donna Thal University of California, San Diego

Kimberly Whitesell University of California, San Francisco

Larry Fenson San Diego State University

Lisa Oakes University of Texas, Austin

Whether language/gesture correlations in early language development can be explained by parallelism or comprehension mediation was examined. Study 1, parental report data for 95 l-year-olds, suggested that word comprehension and production are dissociated in this age range and that the comprehension and production factors map onto distinct aspects of gesture. Study 2 tested 41 13-15- month-olds in a task in which the modeled gesture was accompanied by supportive, contradictory, or neutral narratives. Results showed that infants can use adult speech as an aid in reproduction of modeled gestures (comprehension mediation). However, there is still additional variance in gestural production that correlates with expressive vocabulary when comprehension-related variance is removed. Thus, comprehension mediation and parallelism both appear to be operating.

Before they are 18 months old, most children discover the idea that things have names (i.e., that words can be used to recognize, request, label, categorize and represent objects in the world). This discovery is preceded by evidence for word comprehension and is either preceded or accompanied by the use of conventional gestural schemes in communication or in play with objects, or in both. Piaget (1962) and Werner and Kaplan (1963) have argued that this temporal synchrony is no accident. Their approach is based on the idea of parallelism (i.e., that linguistic and gestural schemes for objects are related in early development because they both depend on a common underlying symbolic function). Thus, word comprehension, word production, and symbolic play are clear, public manifestations of a much more general cognitive shift from sensorimotor process- ing to the use of symbols in many aspects of thinking, problem solving, and communication (for reviews see Bates, Bretherton, Shore & MeNew, 1983; Leonard, 1988; Shore, Bates, Brether- ton, Beeghly, & O'Connell, in press; Shore, O'Connell, & Bates, 1984; Voiterra & Caselli, 1985).

The Piaget/Werner hypothesis has been influential, but it is also controversial. A host of correlational studies appeared across the 1970s and 1980s, examining associations and dissociations between early language and other sensorimotor domains (for reviews, see Bates, O'Connell, & Shore, 1987; Bates & Snyder, 1987; Harris, 1983; Johnston, 1985). In general, these studies provided evidence against a global, cross-domain stage shift from sensorimotor to symbolic functioning (see also Uzgiris & Hunt, 1978, 1987). Summarizing, some nonlinguis-

This research was supported by a grant from the John D. and Cather- ine T. MacArthur Foundation Research Network on the Transition From Infancy to Early Childhood, and by a National Institutes of Health First Investigator Award (PHS NS 19639) to Donna Thai.

Correspondence concerning this article should be addressedto Eliza- beth Bates, Department of Psychology C-009, University of California, San Diego, La Jolla, California 92093.

tic measures are indeed reliably correlated with the emergence of naming (e.g., means-end behaviors or tool use, and aspects of symbolic play). However, several other cognitive domains appear to be completely dissociable from early language (e.g., spa- tial cognition and traditional tests of object permanence).

Because the Piaget/Werner hypothesis appears to have failed in its strongest form (i.e., single-factor parallelism), some investigators have argued that language develops along a matura- tional course that is independent from other aspects of cognition (Curtiss & Yamada, 1978; Curtiss, Yamada, & Fromkin, 1980; Harris, 1983; Petitto, 1988). Such developmental independence would provide support for Chomksy's long-standing argument that language is an autonomous, encapsulated, "modular" cognitive system (Chomsky, 1965, 1980; Fodor, 1983; Roeper & Williams, 1987). However, strong arguments for autonomy (like strong arguments for parallelism) are not easily reconciled with the fact that at least some aspects of non- verbal cognition (e.g., symbolic play) are reliably associated with progress in language. There appears to be room for compromise between these two strong positions.

A number of investigators have offered compromise views to explain the relation between language and cognitive development, alternatively referred to as local homology (Bates, Be- nigni, Bretherton, Camaioni, & Volterra, 1977), skill theory (Corrigan, 1978; Fischer, 1980), and the specificity hypothesis (Gopnik & Meltzoff, 1986, 1987). Although they differ in detail, these theories are all based on the claim that language-cognition relations are many-to-many rather than one-to-one. Lan- guage itself is composed of many separate, underlying skills or mechanisms. Some of these components may be specific to language; other components are shared by several cognitive domains, resulting in significant cross-domain correlations at those points in development when a shared component is "com- ing on line."

Working within this revisionist framework, we have been try- ing to improve our understanding of the cognitive mechanisms

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shared by word comprehension, word production, and symbolic gesture in the second year of life. Most of our work has focused on the relation between early language and one particular type of gesture: the action schemes associated with familiar toys and household objects (e.g., drinking from cups, putting hats on heads, placing a telephone receiver near the ear). These gestures are often used by 1-year-olds to recognize an associated object or event, and they form the primitive beginnings of the activity referred to as symbolic play (Inhelder, Lezine, Sinclaire, & Stembak, 1971; Lezine, 1978). Because they appear to serve a recognitory function in the early stages and are subsequently used in empty-handed pantomimes with inappropriate versions of the object to confer the appropriate object meaning, these action schemes have been referred to as enactive names (Esca- lona, 1973) or gestural depiction (Werner & Kaplan, 1963).

The symbolic status of these and other forms of gesture in infancy is discussed in detail by Bates et al., (1983). They presented a classification scheme for infant gesture that involves six features: (a) learned through imitation, (b) used in communication (at least part of the time), (c) used to establish reference to external objects or events, (d) used to refer to specific individ- uals or classes of objects or events, (e) used at some physical distance from the referent object, and (f) presented and ac- quired within a conventional system of other symbols or signs. Vocal names and American Sign Language (ASL) signs share all six of these features. Other forms of gesture share only a subset, permitting us to classify gestures according to their degree of overlap with "true" symbols or names along these theoretical dimensions. For example, showing-off games like "bye- bye" and "pattycake" overlap with language along the first two features (they are derived through imitation and are used in communication). So-called deictic gestures (giving, showing, and pointing) share the second and third features (communicative use and establishment of reference); unlike giving and showing, the pointing gesture also shares the fifth feature (distance from the referent). Recognitory gestures with objects (e.g., drinking from a cup, putting on a necklace) share the first (imitation), third (reference), and fourth (reference to specific classes of objects or events) features. When the same gestures are carried out with substitute objects or in empty-handed pan- tomime, then we could argue that they inherit two additional features of true symbols: use in communication (Acredolo & Goodwin, 1988; Volterra & Caselli, 1985)and execution at some physical distance from the real object or class of objects that the gesture names or represents (Volterra, Bates, Benigni, Bretherton, & Camaioni, 1979).

This analysis provides a theoretical justification for predicting correlations between language and various forms of gesture in the first and second year of life. Using these criteria, Bates et al. (1983) concluded that recognitory gestures or enactive names share more overlap with language than do any other aspects of gesture (except, of course, for the true linguistic signs of ASL)--particularly when the gestures are observed or elicited out of context, without the usual referent object in hand. Hence, these gestures ought to bear the strongest and most con- sistent relationship to the development of naming in the vocal modality. There is now a large empirical literature supporting this prediction, demonstrating a link between recognitory ges-

tures (also called primitive symbolic play) and the emergence of naming, in normal infants and in several different populations of retarded or language impaired children. These include links in time of onset, function, frequency of use, size of repertoire, content, rates of "decontextualization," individual differences in style, and some neuropsychological evidence suggesting that language and symbolic/recognitory gestures share aspects of left hemisphere control (Bates et al., 1977; Bates, Benigni, Bretherton, Camaioni, & Volterra, 1979; Bates, Bretberton, Snyder, Shore, & Volterra, 1980; Bates & Volterra, 1984; Bauer & Shore, 1986; Curcio, 1977, Eider & Peterson, 1978; Golden- Meadow & Mylander, 1984; Gopnick & Meltzoff, 1987; Killen & Uzgiris, 1981; Lezine, 1978; Nicolich, 1977; Snyder, Bates, & Bretherton, 1981; Volterra et al., 1979; Wolf & Gardner, 1979; for reviews see Bates & Snyder, 1987; Harris, 1983; John- ston, 1985). Similar links have also been demonstrated for a number of clinical populations (Beeghly & Cicchetti, 1987; Roth & Clark, 1987; Sigman & Mundy, 1987; Snyder, 1977; Terrell, Schwartz, Prelock, & Messick, 1984; T h a l & Bates, 1988a; Thal, Bates, & Bellugi, in press). In short, evidence in favor of some kind of parallelism between language and gesture appears to be quite robust, even when investigators control for factors like Global Maturation or Mental Age. Results are particularly strong when contextual factors are controlled (e.g., Bates et al., 1980).

This does not mean that recognitory gestures and vocal names are identical (cf. Petitto, 1988). There are some important differences between linguistic names and recognitory gestures that must also be taken into account in models of language/gesture relations (for a review, see Shore et al., in press). For example, Zukow (1984) has argued that symbolic play grows out of social interaction and that the symbols children use in play never achieve the independent cognitive status of linguistic symbols. This claim is compatible with a report by Bretherton, Bates, Benigni, Camaioni, and Volterra (1979), that attachment scores correlate with symbolic play but not with vocal naming. K. Nelson (1985) has also argued that action schemes with objects are not true symbols, or at least not as symbolic as words for the same object (see also Huttenlocher & Higgins, 1978). Nelson's argument is supported by the finding that recognitory gestures can develop weeks or months earlier than vocal names in some children (Thal& Bates, 1988b) and by studies showing that recognitory gestures are affected more strongly by characteristics of the referent object (e.g., whether the object is in the child's hand and whether it is a detailed and realistic version of the "real thing" "Bretherton, O'Connell, Shore, & Bates, 1984). There are also studies showing that measures of symbolic gestures are less reliable (i.e., lower intermea- sure correlations) than corresponding measures of language (Bretherton & Bates, 1984).

Most of these differences can be handled by models that permit degrees of symbolic status (e.g., the six-feature model proposed by Bates et al., 1983). However, Petitto (1988) has presented an argument against language/gesture parallelism that is (potentially) much more damaging. Specifically, she has suggested that language/gesture correlations reflect the fact that children use adult speech as a guide during their play activities (i.e., comprehension mediation). For example, suppose that an

1006 BATES, THAL, WHITESELL, FENSON, OAKES

adult playmate says "Mmm, that bear looks hungry; give him something to eat." If a child understands this input, the likeli- hood of a bear-feeding sequence is considerably enhanced. Such causal effects of adult language on child play could account for positive correlations between symbolic play and language comprehension scores. Meanwhile, there is also a significant positive correlation between language comprehension and language production. This correlation reflects a "true" homology (i.e., the fact that comprehension and production make use of a common lexical base). This mix of causal relations results (indi- rectly) in a positive correlation between symbolic play and language product ion--a correlation that proponents of parallelism (mistakenly) interpret to mean that vocal naming and recognitory gestures are manifestations of a common symbolic function. If we accept this logic, then correlations between language production and symbolic play actually reflect nothing more than a correlation of language with itself.

There are a number of reasons why comprehension mediation may not be sufficient to account for all of the correlational patterns between language and gesture that have been observed in the literature to date. For one thing, language comprehension and language production are typically not highly correlated in the first 2-3 years of life (Bates, Bretherton, & Snyder, 1988; Snyder et al., 1981 ). This fact presents problems for the correlational logic described earlier. Indeed, when comprehension and production are dissociated, specific links between word production and gestural production are still observed (Bates et al., 1980; Thai & Bates, 1988a, 1988b). Furthermore, there is evidence suggesting that word comprehension and word production correlate with different aspects of communicative and symbolic gesture (Bates et al., 1980).

But these arguments are still not sufficient to put the mediation account to rest. There are, in fact, at least two possible forms of linguistic mediation that could be responsible for language/gesture correlations in 1-year-old children. First, the child may use the language provided by others as a retrieval cue for gestural activity (i.e., comprehension mediation). Second, she may use her own covert or overt language production as a guide to action (i.e., production mediation). In view of these confounds, we believe that a more detailed exploration of language/gesture relations is in order, in a design that permits us to disentangle the dissociable effects of comprehension and production. The distinction between parallelism and linguistic mediation is important not only because the two hypotheses reflect fundamentally different views of language and thought, but also because the two views have different implications for research and practice with language disordered children. The parallelism hypothesis has been particularly influential in clinical research (Bates & Snyder, 1987; Rice, 1983). Specifically, it has been argued that spontaneous or elicited symbolic play can be used to distinguish between language-specific deficits in toddlers and preschool children and also, between deficits that are due to a more general delay in cognition and representation (Kamhi, 1981; Sigman & Mundy, 1987; Snyder, 1975; Roth & Clark, 1987; Terrell et al., 1984). Given the widespread interest in this issue, we think it is important to determine the extent to which i-year-old children can make use of linguistic support to under- stand and reproduce a gestural symbol. If these infants can in-

deed integrate gestural and linguistic representations for objects, we need to determine whether this integration is sufficient to account for the parallels that have been observed between enactive naming and early language development in normal and clinical populations.

To explore these issues, we will present results from two studies that examined the relationships among word comprehension, word production, and enactive/gestural naming. Study 1 makes use of detailed questionnaires administered to the parents of 95 children between 12 and 16 months of age. Here we will show that comprehension and production are each correlated with different aspects of communicative and symbolic gesture. Study 2 is a laboratory experiment with 41 children between 13 and 15 months of age, directly investigating the causal effect of adult linguistic cues on gestural imitation. Our results will show that parallelism and linguistic mediation are both partially correct, each accounting for different aspects of the relationship between language and gesture in infancy.

S tudy 1: Paren ta l Repor t s

Because the words and gestures that we are interested in have just begun to emerge in the 12-16-month age range, it is difficult to obtain a reliable sample of a given child's abilities in a 60- 90-min laboratory visit. It is possible to remedy the problem somewhat by developing elicitation procedures that make the occurrence of target behaviors more likely (see Study 2). But this practice also has its limits, because toddlers are notoriously difficult to test. For these reasons, we have found it useful to supplement naturalistic or structured observations, or both, with information obtained through parental report. In the present study we assessed the three-way relations among word comprehension, word production, and gestural production, using a checklist-style instrument that permitted the parent to rely on recognition memory rather than recall.

The inventory used in Study 1 is one of two that have been developed and validated in our laboratory over the past 15 years. Each inventory takes the form of a list of vocalizations, words, gestures, grammatical morphemes, or word combinations that are typical of children within a particular age range. Parents were asked to fill these out at home over a few days, so that they could observe their child while they had the questionnaire in mind, and identify as many examples as possible. Thus, a list of the child's current behaviors as they occurred across many contexts was obtained. This information proved to be far more reliable than retrospective reporting, and more representative than 2 or 3 hours of observational data in this age range. The validity and reliability of these inventories, as well as their pre- dictive value, has been demonstrated in a number of studies (Bates, Benigni, et al., 1979; Bates, Snyder, Bretherton, & Vol- terra, 1979; Bates et al., 1980; Bates et al., 1988; Bretherton et al., 1984; Dale, Bates, Reznick, & Morisset, 1989; Dale & Robinson, 1988; Epport, 1988; Goldfield, 1988; O'Brien, 1988; Reznick & Goldsmith, 1989; Snyder et al., 1981; Tamis-LeM- onda & Bornstein, 1989; Thai & Bates, 1988a). Positive results have also been obtained in other laboratories with parental report instruments that were similar to ours (Acredolo & Good- wyn, 1988; Rescorla, in press; Rescorla & Schwartz, 1988).


Method

Subjects. Subjects were 95 children between 12 and 16 months of age. They were chosen from a subset of more than 500 children partici- pating in a large-scale study in progress in San Diego, to provide age- graded norms for parental report instruments of language and communicative development of children between 8 and 30 months of age (Fenson, Vella, Flynn, & Thal, 1988). All of the children chosen for the present study had reported production vocabularies of under 100 words, a relatively homogeneous stage of language development for which the literature suggests that language/gesture correlations are the- oretically interesting and relatively large.

Children and their parents were identified and recruited in several ways--through advertising in local newspapers and contacts made through area pediatricians and day-care centers. Parents were initially contacted by telephone or letter; if they agreed to participate, we sent them copies of the Language and Gesture Inventory (Bates et al., 1986; described under Materials), with a stamped, self-addressed envelope for return. We also included a simple subject-information sheet that in- quired about the child's developmental history and contained questions about the parents' occupation, education, and the language(s) spoken in the home. All of the children selected for the norming study were acquiring English as their first language, and none had a significant history of birth trauma or other serious medical problems (as indicated on the information sheet). Most of the children chosen for this study were from middle-class and upper middle-class homes (as determined by parental occupation and education), although some working-class families were included in the sample.

Materials. Part 1 of the Language and Gesture Inventory is composed of a list of 500 words, organized into semantic categories (e.g., food words, bedtime words) that are likely to appear in the vocabularies of young English-speaking children within the 2nd year. Parents were asked to check those words that their child produced (column l) or comprehended (column 2). This part of the questionnaire has been developed and validated in several previous studies and has proven to be a reliable and valid predictor of observed language comprehension and production across this age range (Bates et al., 1987; Dale & Robinson, 1988; Snyder et al., 1981). Part 2 of the questionnaire is a list of 64 gestures that are frequent in the repertoires of l-year-old children in our culture; the list includes communicative routines like "bye-bye" or "pattycake," deictic gestures (i.e., giving, showing, pointing), and object-associated gestures that may occur in communication or in play (e.g., "drinking," "telephoning"). The parents were asked simply to check those gestures or actions that they have seen their child produce. The complete gesture list was developed for the present study; however, previous studies in our laboratories have suggested that parental reports of gestural development do correlate with observations of the same phe- nomena in this age range (Bates, Snyder, et al., 1979; Volterra & Caselli, 1985; Bretberton, 1984).

Scoring and data reduction. The following subscale scores were derived from the Language and Gesture Inventory:

1. Word comprehension--total words comprehended, number of nominals comprehended (i.e., names for common objects), and number of nonnominals comprehended.

2. Word production--total words produced, number of nominals produced (as defined above), and number of nonnominals produced.

3. Gesturalproduction--total gestures produced, number of gestures associated with common objects (i.e., enactive names), deictic gestures (giving, showing, pointing, ritual requests), and gestural routines that do not refer to common objects (e.g., "patty-cake," "bye-bye," "so big").

We separated nominals from nonnominals in both comprehension and production, for three reasons. First, on the basis of the Bates et al. (1983) classification scheme, we expected correlations between language and gesture to be stronger when we restricted our attention to

Table 1 Descriptive Statistics for Parental Report o f Language and Gesture

Measure M SD Range

Comprehension Total 121.03 67.09 9-297 Nominals 55.54 32.51 2-128 Nonnominals 65.49 36.94 6-169

Production Total 25.00 20.78 0-83 Nominals 13.93 12.59 0-46 Nonnominals 11.07 9.15 0-41

Gesture Total 37.45 9.07 13-52 Object gestures 24.03 7.17 6-39 Deictic gestures 3.55 0.71 1-4 Gestural routines 9.87 2.88 0-15

object-related terms (i.e., recognitory gestures with common objects, and vocal names for common objects). Second, previous research has shown that within-language correlations are higher when attention is restricted to general nominals (e.g., Bates et al., 1988); hence, a separa- tion of nominals and nonnominals should help to clarify the nature and degree of any comprehension/production dissociation observed. Third, recent studies have suggested that children who have a higher proportion of common nouns in their vocabularies may show a different pattern of development in communicative gesture and symbolic play (Bauer & Shore, 1986).

Descriptive statistics were examined for all 10 scores to provide information about the size and composition of comprehension, production, and gesture repertoires in this developmental period. The 7 subscale scores (excluding totals) were also factor analyzed (principal component analysis with varimax rotation). If some form of the local homology model is correct, then we should expect to find at least two distinct factors (defined by word comprehension and word production, respectively), each with a different pattern of loadings from the three gesture scores.

Resul ts and Discussion

Table i summar i ze s descriptive statistics for the 10 language and gesture scores. There are no surprises here; findings f rom the parenta l repor t i n s t r u m e n t are largely compat ib le with di- ary studies and labora tory observat ions by other investigators working in this age range.

According to thei r parents , mos t of these chi ldren already had substant ial comprehens ion v o c a b u l a r i e s - - a n average of 121 words, with a range from 9 to 297. Slightly less than one ha l f o f these words were names for objects (M = 55.5, with a range f rom 2 to 128). By contrast , the same chi ldren p roduced an average of only 25 words (with a range from 0 to 83). Slightly more than one ha l f of these, on the average, were names for objects ( 13.9, with a range from 0 to 41 ).

In the sample as a whole, comprehens ion and p roduc t ion were correla ted at +.46; a l though this corre la t ion is reliable (p < .01), it also means tha t comprehens ion and p roduc t ion share less than 22% of thei r variance. Figure 1 presents a scatterplot of total comprehens ion and p roduc t ion scores for all the chi ldren in this study. The positive l inear t rend responsible for


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C O M P R E H E N S I O N

Figure 1. Scatterplot of total comprehension and production scores of 95 children between 12 and 16 months of age, as reported by parents on the Language and Gesture Inventory.

a +.46 correlation can be discerned in Figure 1, but it is equally clear that the two modalities are dissociated in many children. At almost every point along the comprehension range (from 0 to 250 words), we found at least a few children who were producing fewer than 10 word forms. This pattern replicates a scatterplot of comprehension/production relations reported by Snyder et al. (1981) for a sample of 32 children, and it is compatible with many reports in the literature on the extent to which receptive and expressive language development can be dissociated in the early stages.

Turning to results of the gestural scale (see Table 1), these children produced an average of 37 gestures, with a range from 13 to 52. These included a mean of 24 object-associated gestures (ranging from 6 to 39), 9.87 gestural routines (from 0 to 15), and 3.55 out of the 4 possible deictic gestures (with an observed range from 1 to 4). Most of the children reportedly gave and showed objects to their parents, and produced some kind of ritualized gesture in requests (e.g., opening and shutting the palm); hence, much of the variance in the deictic gesture subscale reflects presence or absence of pointing.

Table 2 summarizes correlations among all 10 language and gesture scores. In the sample as a whole, total gesture vocabularies were significantly correlated with word comprehension (r = .57, p < .001 ) and word production (r = .54, p < .00 i). However, we also found evidence for a dissociation between gestural production and expressive language in children at the earliest stages of language learning. In the subsample of children with expres-

sive vocabularies of 10 words or less, the average number of gestures reported was 31.3 (with a range from 13 to 47)--only slightly smaller than the average for the sample as a whole. These children had an average of 2.5 words for common objects (with a range from 0 to 6), but they reportedly produced 19.7 object gestures (with a range from 6 to 35). There was not one case of a child in this developmental range who produced more object words than object gestures--despite the fact that the total list of possible words that the parent could have checked was considerably longer than the list of possible gestures. By contrast, reported language did sometimes surge ahead of gesture among the more precocious talkers in the sample (although, of course, here the difference in length in the two check- lists presents a possible confound).

These results are consonant with the evidence we reviewed earlier on similarities and dissimilarities between language and gesture. Recognitory gestures and vocal names usually appear around the same time in development, but the vocal modality sometimes lags behind. However, despite these asynchronies in total scores, total scores for gesture and for language were still correlated in the subsample of children with smaller vocabularies (r = .56, p < .01).

A principal components factor analysis was conducted on the seven word and gesture subscales, to determine whether comprehension and production do indeed form two separate factors, and to examine factor loadings for each gesture type. Age in days was also included in the factor analysis, to determine whether and to what extent the resulting factors are defined by effects of maturation and/or experience. Factor loadings after rotation are summarized in Table 3.

Results provide support for a two-factor model defined by word comprehension and word production, respectively. The principal components analysis yielded two factors with eigenvalues greater than 1.0. The first factor (accounting for 47.5% of the variance, eigenvalue = 3.80) was defined primarily by word production (both nominals and nonnominals). The second factor (accounting for 13.7% of the variance, eigenvalue 1.09) was defined primarily by word comprehension (again, both nominal and nonnominal). Although age did load positively on both factors, its contribution was relatively small; neither of the factors was in any sense defined by variance in age. Note, however, that age loadings were somewhat higher on the Production factor (.45) than on the Comprehension factor (.27).

Because the factor analysis maximizes orthogonality between factors, we must interpret this comprehension/production dissociation as follows. Factor 2 reflects that portion of the variance in word comprehension that is partially dissociable from the child's current level of expressive language; we might con- sider this the conceptual content of the child's current symbol system. Conversely, Factor 1 reflects that portion of the variance in word production that is partially independent from the child's level of language comprehension. Interpretation of this factor is less obvious, but it may involve a tendency toward rote imitation or motor abilities that are partially independent of conceptual understanding (cf. Bates et al., 1988). This distinction will be helpful in interpreting the gestural loadings on each factor.

Gestural routines load significantly on the Production factor

LANGUAGE AND GESTURE

Table 2 Correlations Between Language Comprehension, Language Production, Gesture Production, and Age

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Comprehension Production Gestures

Total Non- Total Non- Object Deictic Gestural Measure Age w o r d s Nouns nominals w or ds Nouns nominals T o t a l gestures gestures routines

Age Comprehension

Total words .24* - - Nouns .29** .96*** - - Nonnominals .17 .97*** .87*** - -

Production Total words .35*** .45*** .43*** .43*** - - Nouns .32** .42*** .41"** .39*** .97*** Nonnominals .35*** .44*** .41"** .44*** .94***

Gestures Total .44*** .57*** .50*** .54*** .54*** Object gestures .48*** .56*** .56*** .52*** .46*** Deictic gestures .23* .28** .28** .26** .23* Gestural routines .13 .32*** .28** .35*** .47***

.82***

.52*** .50*** - -

.46*** .42*** .95*** - -

.23* .21" .41"** .32** - -

.43*** .50*** .68*** .43*** .26**

*p<.05. **p<.01. ***p<.001.

(.64), with negligible loadings on the factor defined by word comprehension (.22). Deictic gestures load primarily on the Comprehension factor (.40), contributing less to the factor defined primarily by word production (.24). Finally, object-associated gestures load significantly on both factors, although they contribute more variance to the factor defined by comprehension (.63 vs..47). This pattern makes sense if we keep the afore- mentioned interpretation of the two factors in mind. Factor 1 reflects aspects of performance that are at least partially independent of conceptualization: social motivation, motor development, imitative abilities, or some combination. This may explain why gestural routines like "bye-bye" and "pattycake" load most heavily on Factor 1. Factor 2 is best regarded as reflecting symbolic/conceptual content. Object gestures and deictic gestures load on this factor because they reflect the child's understanding of the object world and his or her interest in com- municating that understanding.

At least two different mechanisms appear to be responsible for the patterns of variation observed here, associated with the observed dissociation between word comprehension and word production. Object-associated gestures (i.e., enactive names) are indeed associated with language comprehension, in line with the comprehension mediation hypothesis. However, some of the variance in enactive naming is also independently associated with language production, suggesting that several different processes may be at work. In the next study, we will focus en- tirely on the relationship between object-associated gestures and vocal names, in an experiment designed to test the comprehension mediation hypothesis directly. Because recognitory gestures will be assessed under several different conditions, it may be easier to pull apart the separate contributions of comprehension and production.

Study 2: Elici tat ion of Ges ture With and Wi thou t Linguist ic Suppor t

Study 2 was designed to meet several of the theoretical and empirical issues raised in the language/gesture literature.

First, we began our session by taping a brief sample of spontaneous play with realistic versions of the object concepts to be used in the experimental study. This segment closely resembles the conditions under which symbolic play is assessed in most observational studies, and therefore offers some useful points of contact and contrast between this study and other reports in the literature. The spontaneous segment is also more similar to the conditions under which parents usually observe their children at play, and hence may help to illuminate the correlational results we obtained with parental reports of gestural development.

Second, we set up an experiment in which children were required to reproduce familiar gestures using a colored wooden or plastic block as a placeholder for the referent object. This allowed us to assess the child's ability to produce recognitory gestures without support from the usual referent object, an ability that bears a stronger theoretical relationship to "true" naming.

To address the comprehension mediation hypothesis, gestures were modeled under three conditions of verbal accompa- niment: supportive language (with the object correctly named),

Table 3 Factor Loadings in Study 1

M e a s u r e Communalities Factor 1 Factor 2

Word comprehension Nominals .8811 .1851 .9202 Nonnominals .8400 .1903 .8966

Word production Nominals .7883 .8630 .2085 Nonnominals .8224 .8829 .2068

Gestures Object gestures .6094 .4669 .6256 Deictic gestures .2219 .2414 .4045 Gestural routines .4587 .6412 .2182

Age .2762 .4535 .2657


contradictory language (with an object appropriate to a different gesture named), and neutral language (with no specific reference to either the object or the action). This allowed us to assess systematically the extent to which a given child 's production of object-associated gestures was affected by comprehension of the associated words.

Finally, because we wanted to assess gestural performance under precisely controlled input conditions, we relied primarily on elicitation of gestures instead of spontaneous production. Fenson and Ramsay (1981) have shown that elicitation procedures yield earlier and possibly more reliable estimates of symbolic play, while following the same developmental sequence observed in spontaneous symbolic play (Fenson & Ramsay, 1981).

M e t h o d

Subjects. The sample for Study 2 was composed of 41 children (20 boys and 21 girls) between 13 and 15 months of age. There were 14 children at 13 months of age, 13 at 14 months, and 14 at 15 months; both sexes were equally represented within each age bracket. Slightly more than one half of the subjects were only children. Most of the rest had one older sibling, and a few had two older siblings. All of the children were acquiring English as their first language.

Children and their parents were recruited through two sources: a university subject pool drawn from state birth records, and advertisements in local newspapers. Those parents who agreed to participate in the present study were all from middle-class backgrounds (based on reported occupation and/or place of residence). Parents filled out the Lan- guage and Gesture Inventory, described in Study 1, approximately 1 week before they brought their children to our laboratories to participate in the experimental study. Questionnaires were scored after the laboratory session was complete; thus, experimenters were blind to the child's reported levels of ability in language or gesture at the time testing took place.

Procedure. On the basis of previous studies of the objects, words, and gestures that first appear in the repertoires of infants in their second year (Appendix), 12 object concepts were selected for the elicited gesture task. Our selection of these 12 object concepts was guided not only by their relative frequency in early childhood, but also by the extent to which associated gestures could be recognized and distinguished without the object in hand. For example, even though "cup" and "bottle" are both very likely to occur in the repertoires of l-year-old children, the gestures associated with each object (i.e., drinking) would be difficult to distinguish in an experimental context. Hence, we chose only one object concept associated with a drinking gesture (i.e., cup), only one vehicle concept associated with a moving-back-and-forth gesture (i.e., car), and so forth.

Testing was conducted in a room equipped with a video camera, a low couch, and a table with four chairs. When the children arrived at the laboratory, they first spent 15-20 min seated next to the experimenter, directly in front of the couch on which their mothers were seated. The experimenter presented a standard set of toys to the child, one at a time, and allowed the child to play with each item for up to 2 min. The toys were always presented in a context of naturalistic free play. All of the toys were realistic versions of the 12 object concepts that would be the focus of the experiment itself. If the child spontaneously produced a conventional action usually associated with the target object within the 2 min (e.g., drink from the cup, push the car back and forth across the floor), the next item was presented. Most children produced at least some conventional gestures within the first 30 s, and a new object was presented. For most children, this whole sequence usually lasted about 15-20 rain. If the child did not spontaneously carry out the associated

action, that action was modeled once by the experimenter with the object in hand. After modeling, the object was handed back to the child for approximately 30 s. If the child still did not produce the gesture, the modeling procedure was repeated one more time.

During the free play segment, no attempt was made to control or direct mother-child interaction, and all three participants usually inter- acted with the toys presented. Thus, it was more naturalistic than the highly structured gesture elicitation experiment described in the following paragraph. In addition, the extent to which adults named or described toys during the interaction was not controlled in free play.

The elicited experimental condition took place at a table removed from the play area (with all the realistic toys placed out of sight). The child was seated across the table from the experimenter, on his or her mother's lap. Nine target gestures were modeled for each child, one at a time, using a block as a placeholder for the particular object (e.g., for the phone gesture, the block was held to the ear as if it were a receiver; for the cup gesture, it was tilted up to the lips). Blocks were used rather than real toys to ensure that the presented words and gestures were the only sources of information given to the child concerning the object concepts. They were varied with each imitation by choosing a different block from a pool of l0 that had different shapes, sizes, and colors. One half were made of wood and the other half of plastic. Each gesture was modeled in one of three language support conditions: supportive, neutral, or contradictory. Thus, each child was asked to imitate three gestures presented with supportive language, three presented with neutral language, and three presented with contradictory language. In the supportive condition, the experimenter named the object referred to by the gesture (e.g., "Look! This is a cup!"). In the neutral condition she made a nonspecific comment like, "Look! Watch this!" In the contradictory condition she misnamed the object (e.g., by saying, "Look! This is a shoe," while modeling the phone gesture). In order to avoid contamina- tion or interference between trials, the three inappropriate words used in the contradictory condition were always chosen from the set of three familiar object concepts that were not presented as gestures at any point. Hence, no concept was ever repeated in word or gesture to any one child. All of the concepts were rotated randomly so that each occurred in every condition (supportive, neutral, contradictory) an equal number of times.

Of the four places in which each object concept could appear--as gestures in the three word conditions or as a word in the contradictory condition--presentations were arranged so that each concept appeared an equal number of times in each condition, to control for the possible unique effects of any one concept. The order in which the nine gestures were presented was uniquely and randomly assigned for each child.

A practice trial, using a camera gesture, preceded presentation of the test items. The experimenter held a block as though it were a camera and pretended to take the child's picture. Then she gave the block to the child and said, "Can you take my picture?" The purpose of the trial was to introduce the child to the imitation game. The child was encouraged to imitate and was praised if he or she did. After this trial, the experimenter no longer differentially reinforced imitation, but smiled and said something supportive but unrelated to the child's behavior (e.g., "So that's what you want to do with that block"). After each gesture was modeled, the experimenter said, "There, your turn," and handed the block to the child. The child was allowed a minute or two in which to produce (or not produce) the modeled gesture. If the child did not imitate within the first minute, or if the child had clearly failed to attend to the first model, the gesture was modeled a second time. No more than two models were given on any trial. The parent remained with the child throughout the session but was asked not to name any of the concepts presented or to encourage the child in the performance of any imitations.

Data reduction and dependent measures. Performance in the free


play segment and in the testing phase of the experiment was scored directly from videotapes. Each child was given two scores for the free play segment. One score reflects the number of target gestures that were produced spontaneously, prior to the experimenter's intervention ( 1 point each, with a possible range from 0 to 12; repetitions of the same gesture were not counted). The other score reflects the total number of target gestures that were produced in the free play segment as a whole (spontaneously or after the experimenter began to elicit gestures with the realistic object; 1 point each, yielding a possible range from 0 to 12 with no points given tbr repetitions).

In the experimental phase, children received 1 point for each trial in which they produced a recognizable imitation of the adult model. Thus, the maximum score that could be obtained by any child was 9 points across conditions and 3 points within each condition. An assistant scored approximately one half of the tapes, and the experimenter scored the other half. The experimenter also scored 10 of the videotapes scored by the assistant. Interrater agreement for the number of imitations scored on these 10 tapes was 99%.

In addition to the gestural scoring, we were also interested in the extent to which children repeated the experimental words and the spontaneous production of words or wordlike sounds associated with the experimental objects (including sound effects like "'vroom" or "yum"). All recognizable words or vocalizations that met these criteria were transcribed directly from the videotapes. We did not score vocalizations that were unrelated to the 12 target objects (e.g., "Mama;" "more: ' or "no").

On the basis of the number of words in each child's comprehension vocabulary (as reported in the parental inventory), children were divided as evenly as possible into three comprehension level groups: low (9-57 words, n = 14), mid (60-118 words, n = 14), and high (131-233 words, n = 13). The purpose of this between-subjects manipulation was to provide a further test of the hypothesis that production of symbolic gestures is a function of comprehension mediation. The comprehension groups were used in one-way analyses of variance (ANOVAS) on gestural performance in the free play segment, and in 3 × 3 analyses of the gesture experiment (with comprehension group as a between-subjects factor, and language input condition as a within-subjects factor).

We carried out additional analyses by dividing the children into two groups, based on their reported production vocabularies. We used only two groups instead of three for production because there is so much less variance in expressive vocabulary in this age range. One half of the sample (n = 21 ) received scores of 10 or less; this corresponds to a stage in which vocabulary development is still quite unstable, with new words appearing and then disappearing for weeks at a time (Vihman, 1986). We will refer to this group as the low producers. The remaining high producers (n = 20) all reportedly produced more than 10 words. Two children in this group obtained scores over 50, the vocabulary boundary that often presages a marked increase or burst in lexical development (K. Nelson, 1973. 1981 ). On theoretical grounds, these children may be qualitatively different from the others, but there were too few to permit a third expressive language group. The two resulting production groups were used as a between-subject variable in analyses of the free play segment and in 2 x 3 analyses of gestural performance across the three experimental language input conditions.

Ideally, we would like to treat comprehension and production groups as orthogonal factors in a complete design, yielding a 3 × 3 × 2 (Lan- guage Input Condition × Comprehension Level × Production Level) mixed between- and within-group ANOVA. But only 4 children fell within the requisite high-production/low-comprehension cell in such a design, precluding meaningful analysis. This pattern is of course in line with the comprehension/production results reported in Study 1, which suggested that comprehension is a necessary but not sufficient condition for the development of expressive language.

Results

Free play segment. Table 4 presents descriptive statistics for gestural performance in the free play segment, compared with performance on the same 12 gestures according to parental report, for the group as a whole and for the respective comprehension and production subgroups. Parents reported that children produced an average o f 7-8 of the 12 target gestures (with a range from 3 to 11). Rates of spontaneous production were considerably lower (averaging 3,49, with a range from 0 to 8); however, with the experimenter 's intervention, total rates of gestural production in the free play segment reached an average of 6.09, with a range from 1 to 10. Hence, the parents ' estimates were roughly comparable with rates observed in the laboratory, when performance was supported by the object (realistic toys) and by adult vocal and gestural input.

As can be seen from Table 4, the number of gestures in the parental report and gestural performance in the free play segment both increase as a function o f reported comprehension level. A one-way ANOVA by comprehension group was significant for reported gesture, F(2, 37) = 9.64, p < .001. In this analysis, the linear component was quite reliable, F ( I , 37) = 17.78, p < .001 ; there was no significant nonlinear component (in contrast with some of the experimental analyses presented later). A similar one-way analysis on spontaneous gesture also reached significance, F(2, 37) = 4.10, p < .03; here too there was a significant linear component , F(1, 37) = 7.88, p < .01, but no nonlinear trend. Finally, a one-way analysis of total gesture in the free play segment also yielded a significant comprehension group difference, F(2, 37) = 6.44, p < .01; the linear component was also significant, k~ 1, 37) = 9.62, p < .01, and the nonlinear component just missed significance, F(1, 37) = 3.26, p < .08. The nonlinear trend reflects a leveling of fofges- tural performance between the middle and high comprehenders (an average of 4.64 gestures by the low group, compared with 6.86 and 6.85 by the middle and high groups, respectively). Hence, the comprehension group difference appears to reach ceiling when gesture is assessed under conditions o f maximal support (with realistic objects, and with adult gestural and vocal cuing).

In contrast with these orderly relations between language comprehension and gesture, differences in gestural production were small for the two production groups: 7.00 versus 8.47 for reported gestures (tow vs. high, respectively), 3.09 versus 3.90 for spontaneous gestures, and 5.81 versus 6.40 for total gestures in the free play segment. The high/low product ion difference was significant for reported gesture, by a one-tailed t test (p < .03). Analogous t tests o f the differences for spontaneous and total gesture in free play did not reach significance.

To summarize, our findings for observed gesture in a relatively naturalistic situation complement results from Study 1. Spontaneous production of these 12 object-associated gestures tends to increase as a function of language comprehension level. Differences are considerably smaller when children are grouped according to language production levels. However, the child 's reported level o f gestural production varies as a function o f both comprehension and p roduc t ion - - in line with the results o f


Table 4 Gesture Scores as a Function of Re/9orted Language Level

Comprehension groups Gestures with

12 target objects Totals Low Medium High

Production groups

Low High

Parental report M 7.70 5.93 8.21 9.17 7.00 8.47 SD 2.34 2.09 2.08 1.58 2.49 1.95 Range 3-11 3-9 4-I 1 6-11 3-11 4-11

Warmup Spontaneous

M 3.49 2.50 3.71 4.31 3.09 3.90 SD 1.80 1.74 1.63 1.65 1.81 1.74 Range 0-8 0-7 2-7 2-8 0-8 1-7

Totals M 6.09 4.64 6.86 6.85 5.81 6.40 SD 2.11 1.59 1.83 2.15 2.16 2.06 Range 1-10 1-8 4-10 4-10 3-10 1-10

Experiment Totals

M 6.61 4.71 8.57 6.54 5.00 8.30 SD 3.66 3.33 3.56 3.18 2.96 3.61 Range 1-14 2-I 1 1-14 2-12 2-11 1-14

Study 1, in which reported gesture loaded significantly on both the Comprehension and the Production factors.

Experimental results: Analyses by comprehension group. Elicited gesture scores in the experimental segment were entered into a 3 x 3 mixed design ANOVA, l with the three comprehension groupings as a between-subjects variable and language- support condition as a within-subjects variable. This analysis revealed a main effect of language support, F(2, 76) = 3.91,/9 < .03; a main effect of comprehension group, F(2, 38) = 3.29, /9 < .05; and a Group Language-Support interaction, F(4, 76) = 3.2 l, p < .02.

With regard to the main effect for language support, children were most likely to imitate in the supportive condition and least likely to imitate in the contradictory condition. Thus, infants between the ages of 13 and 15 months were more likely to imitate a familiar gesture with a block if the accompanying linguistic label or name corresponded to the meaning of the gesture. This suggests that words and gestures do map onto the same common object meanings, even in the early stages of symbol development. It also provides some support for the comprehension mediation hypothesis--although, as we shall see, the support is mixed.

The comprehension group main effect was significant, but in a surprising direction. Mean imitation scores were 3.42 for the low comprehenders, 5.07 for the middle comprehenders, and 4.0 for the high comprehenders. A one-way ANOVA over the three comprehension levels yielded a significant nonlinear component, F(2, 76) = 5.74,19 < .03, but no significant linear term. Thus, although linguistic input did affect the probability of gestural imitation, the child's propensity to imitate was not a simple, linear function of comprehension vocabulary.

This nonlinear relation is also evident in the Group × Lan- guage Support interaction illustrated in Figure 2. Tukey post hoc tests (/9 < .05) indicate that there was no significant differ-

ence among linguistic support conditions in the low compre- benders. In the middle group, imitation was significantly higher in the supportive condition; the neutral and contradictory conditions did not differ from one another. Hence, it is fair to say that language can help gestural production in this group, but contradictory linguistic input is not powerful enough to over- whelm the child's interpretation of the gestural model. In the high comprehenders, supportive language produced significantly higher performance than contradictory language; performance in the neutral language condition fell halfway between (and did not differ significantly from the other two conditions). In this last group, supportive language apparently cannot push performance levels much beyond the levels observed with no linguistic information at all; however, when forced to choose between the adult's action and the same adult's accompanying speech, the high comprehenders are prone to place their trust in linguistic cues.

Notice, nevertheless, that the average number of imitations produced decreases from the middle to the high comprehend- ing groups, in all three conditions. As several investigators have suggested, imitation may be more likely overall in children who are at the midpoint of a developmental milestone--suggesting that these children have a greater need to "sketch out" their new abilities on the plane of action (Harnick, 1978; Kagan, 198 l; Shore et al., in press). In order to obtain a clearer measure of the effects of the independent variables, we decided to remove variance due to overall propensity to imitate from the calcula- tions.

We recalculated responses in terms of the proportion of the

For the analysis of variance (ANOVA) reported here, we used the repeated measures ANOVA option in the Statistical Package for the So- cial Sciences multivariate analysis of variance (SPSS x MANOVA) pro- gram in which tests for sphericity are taken into account.


2 _o

IE

i

supportive

neutral

contradictory

COMPREHENSION GROUP

Figure 2. Effects of linguistic input on total number of gestures imitated for 13-15-month-old children with low, medium, and high levels of word comprehension.

total imitations produced by each child within each language- support condition. Thus, we divided the number of trials on which a child produced a scorable imitation in each language- support condition by the total number of imitations produced across all three conditions. These percentage scores were then analyzed in a 3 × 3 mixed design ANOVA (see Footnote 1) with comprehension group and level of language-support as independent variables (see Figure 3). In this analysis, we again found a significant Comprehension Group x Language-Support Level interaction, F(4, 76) = 4.15, p < .004, illustrated in Figure 3. To explore the interaction further, we first carried out three separate simple effects analyses by comprehension level, within each of the three respective language input conditions. All three comprehension level effects were significant, but they differed markedly in shape. The percentage of gestures occurring in the supportive condition showed a linear increase over comprehension levels, F(2, 76) = 8.43, p < .01, with the nonlinear component just missing significance, F(2, 76) = 3.62, p < .07. The proportion of gestures occurring in the contradictory condition showed a linear decrease with comprehension level, F(2, 76) = 12.84, p < .001, with no significant nonlinear component. Fi- nally, the proportion of imitations occurring in the neutral condition shows no significant effects at all, linear or nonlinear.

These effects are clarified further by Tukey post hoc tests (p < .05) within each comprehension level. Within the low comprehenders, there were again no significant differences as a function of linguistic input; the trend is, if anything, in the opposite direction from the one observed in children with larger comprehension vocabularies (i.e., fewer imitations in the supportive

condition). Within the midlevel comprehenders, gestural imitations were much more likely to occur within the supportive conditions; neutral and contradictory language conditions did not differ. This is identical to the effects reported for raw imitation in the middle group. Within the high comprehenders, gestural imitations were significantly more likely to occur in the supportive and the neutral conditions than in the condition with contradictory language; however, there was no significant difference between supportive language and neutral language.

Because the 14 low comprehenders produced fewer gestures overall, we might ask whether their inability to use linguistic input reflects anything more than a floor effect. This was not the case. Although their total output was low (M = 3.42, with a range from 1 to 7 points, SD = 1.95), the data do not violate assumptions of normality. With 14 low comprehenders in three within-subject conditions, there were 42 scores in all; fewer than 25% of the scores were zeroes within any cell of the design. We conclude that the absence of a language input effect in this group is a straightforward reflection of the fact that they do not comprehend language well enough to exploit it as an aid to gestural production. And yet, they still produced many of the target gestures. Some factor other than comprehension mediation must account for their behavior.

These results suggest that the effect of linguistic input on gestural imitation changes over time. Gestural imitation is un- affected by accompanying language at the earliest stages oflexi- cal development. Language input can play a supportive role at the middle stages, but these children apparently ignored the linguistic cue if it conflicted with the modeled gesture. Finally, sup-

50

40

30

20'

10 i

supportive

neutral

contradictory

COMPREHENSION GROUP

Figure 3. Effects of linguistic input on the proportion of gestures imitated for 13-15-month-old children with low, medium, and high levels of word comprehension.


portive language is apparently unnecessary or not particularly helpful for children at the highest levels of comprehension; however, when there is a conflict between verbal and gestural input, the performance of high comprehenders is negatively affected.

So far it appears that the parallelism hypothesis and the comprehension mediation hypothesis are both correct, but at different points in development and in different children. To obtain further evidence regarding the relation between language abilities and gestural performance, we turn to analyses using language production as a grouping variable.

Analyses by production group. The relative independence of comprehension and production in our parental reports suggests that these two aspects of language may each bear a somewhat different relation to symbolic gesture (cf. Bates et al., 1980). To test this hypothesis, we repeated the Language-Level X Linguis- tic-Input Condition analysis, using expressive rather than receptive vocabulary to define the groups (see Footnote 1).

Not surprisingly, we again obtained a significant main effect of input condition, F(2, 78) = 3.32, p < .05. There was also a main effect of expressive vocabulary, F(1, 39) = 6.18, p < .02, with more gestural imitations produced by the high vocabulary group. However, in contrast with analyses using comprehension level, there was no significant interaction between vocabulary level and input condition, F(2, 78) = .25, ns.

Because the propensity for high vocabulary children to produce more modeled gestures is equivalent across linguistic-input conditions, we can conclude that their advantage in gestural output reflects more than receptive language ability. Compre- hension mediation does occur, but it is not sufficient to account for the developmental relation between language and symbolic gesture at the one-word stage. There may be an additional, specific relation between language production and gesture.

Words and sound effects during the experiment. Meaningful speech was rare in this situation, imitative or not. Only 11 of the 41 children produced any meaningful speech at all across the course of the experiment. Seven children produced one or more sound effects associated with the gesture during their own production (e.g., "whee" with the airplane gesture, "vroom" with the car gesture, drinking noises with the cup gesture, eating noises with the spoon gesture, a marked sniffing noise with the gesture of smelling a flower). Because these sound effects were not produced by the experimenter, such vocalizations must be taken to mean that the child recognized the adult model, adding the relevant sounds in his or her own rendition. There were only seven real words produced in all, by 4 of the 41 children. One child produced three words ("cup' ; "baby; ' and "plane"), another produced two words ("flower" and "dog"), and 2 other children each produced only one word ("doggie" and "'baby;' respectively). Broken down by language condition, 3 followed a supportive model, 4 followed a contradictory model, and none occurred in the neutral condition (where there was no adult model to imitate). Because all seven words matched the adult model, they may constitute instances of vocal imitation.

Although vocal productions were infrequent in this experiment, it is interesting that the vocalization data bear a U-shaped relation to comprehension level: 3 of the 14 low comprehenders produced sound effects, 7 of the 14 middle comprehenders produced sound effects or words, or both, and only 1 of the high

comprehenders produced any vocalization at all (the single word "baby"). With regard to expressive language level (as reported by the parent), 7 of the I 1 children who produced meaningful speech during the experiment had expressive vocabularies of more than 10 words. This difference is in the expected direction, but is not overwhelming.

To summarize, there are similarities between observed vocalizations and observed gestures within the experimental task; vocalizations are somewhat more common for children with high reported vocabularies, but they bear a U-shaped relationship to comprehension level. Because there were too few instances of meaningful speech to justify statistical analyses, these results are merely suggestive. We will return to them later in a discussion of the production mediation account of language/gesture relations.

Factor analysis of parental report and laboratory measures. Principal component analysis with varimax rotation was applied to a selected subset of measures in Study 2 to explore relation between laboratory and parental report measures of language and gesture when cognitive content was held constant (i.e., when all measures pertained to the same set of 12 object concepts). Five measures were selected: scores from the parental report for number of experimental words comprehended, number of experimental words produced, and number of experimental gestures produced; scores from the laboratory session for number of target gestures produced spontaneously in free play; and number of target gestures imitated in the neutral language condition. We focused on the neutral language condition only, in order to obtain a measure of elicited gesture that was maximally independent of language input. Age in days was also included as a variable in the analysis. Table 5 summarizes raw correlations among all six variables; Table 6 summarizes the factor loadings that emerged after rotation.

Because the variables entered into this factor analysis are different in many respects from the variables used in the factor analysis in Study 1, we should not expect identical results. How- ever, the results obtained in these two different principal component analyses are quite compatible. Once again, two factors with eigenvalues greater than 1.0 emerged, with factor loadings summarized in Table 5. The two factors once again reflect a dissociation between word comprehension and word production, analogous in several respects to the two factors that emerged in Study 1. Factor 1 has an eigenvalue of 2.61, and accounts for 43.5% of the variance. Word comprehension loads on this factor at + .85. Factor 2 has an eigenvalue of 1.15, and accounts for an additional 19.3% of the variance. Word production loads on this factor at + .53. Age loads positively on both factors, but it is not the defining variable in either case. As in Study 1, age loads more strongly on the Production factor (.69) than the Comprehension factor (.39).

Of greatest interest here are the factor loadings for the three respective measures of object-associated gesture. Two measures load highly on the Comprehension f a c t o r i t h e number of spontaneous gestures observed in the free play segment (.81) and the number of experimental gestures reported by the parents (.51). Two gestural measures loaded highly on the Production fac- t o r - t h e number of experimental gestures imitated in the lan-

LANGUAGE AND GESTURE

Table 5 Correlations Among a Subset of Measures From the Parental Report and the Laboratory Session

1015

Spontaneous Words Words Gestures Total Variable Age gestures comprehended produced produced imitation

Age Spontaneous gestures .41"* - - Words comprehended .34* .52*** - - Words produced .35** .26* .27* - - Gestures produced .44** .23 .56*** .28* Total imitation .41 ** .01 .05 .25 .30*

*p < .05. **p < .01. ***p < .001.

guage-neutral condition (.87) and the number of experimental gestures reported by parents (.53).

There appears to be a dissociation between the spontaneous gestures observed in a brief laboratory free play segment (with realistic versions of the referent object) and the same gestures elicited out of context (without supporting information from adult language or from the referent object). Our parental report measure appears to be sensitive to both sources of variation, loading on both the Comprehension and the Production factors. This replicates the findings reported in Study 1. These findings also replicate an earlier report by Bates et al. (1980), who found that gestural imitation in a scripted situation correlates with language comprehension, whereas imitation of isolated gestures out of context correlates with language production. Once again, we must conclude that at least two mechanisms are responsible for the relation between language and gesture in this age range, even when we restrict our focus to symbols associated with a common set of object concepts.

Conc lus ion

We began by presenting comprehension mediation and parallelism as competing explanations for the finding that language and gesture develop together. Our results suggest that both hypotheses are correct, accounting for different aspects of the data.

Children in the 12-16-month age range are indeed capable of using adult language as an aid in the acquisition and use of gestural schemes. Evidence in favor of comprehension mediation was apparent in both studies. First, word comprehension and gestural production were highly correlated--part icularly when we considered only those gestures that pointed to or represented objects. Second, the experimental study showed that linguistic input does affect gestural performance.

However, the relation between comprehension and gesture is quite complex, with some surprising curvilinear effects. Lin- guistic input had little or no effect among the low comprehenders, and yet these children did imitate some of the adult gestural models. Children in the middle comprehension group were able to use supportive language to enhance their performance, but they ignored the linguistic cue when it contradicted the adult 's action. Yet another pattern occurred among the high compre- benders; contradictory language suppressed their performance, but supportive language did not increase performance beyond

the levels displayed when the adult provided no linguistic information at all. Comprehension mediation appears to be an option that is available to 1-year-old children, developing within the narrow age window studied here; but it is also apparent that comprehension mediation is not obligatory, nor is it equally effective at every stage of development.

Another curious pattern involves the U-shaped relation between comprehension level and total gestural imitation scores. Imitation was most likely among children in the middle comprehension group. This finding parallels a report by Shore et al. (in press) for a separate sample of 28-month-old infants, and it is compatible with a theory of imitation proposed by Kagan (1981). Specifically, Kagan proposed that imitation is most likely when the model lies just outside the child's current level of competence, that is, when it is neither too easy nor too hard (see also K. E. Nelson & Nelson, 1978). Such U-shaped func- tions are chastening because they alert against the assumptions oflinearity that lie behind the linear correlational statistics used in most developmental studies--including our own--(see Bates et al., 1988, for further discussion ofthis point.)

Table 6 Factor Loadings in Study 2

Measure Communalities Factor 1 Factor 2

Parental report Experimental

words comprehended .7523 .8510 .1675

Experimental words produced .3770 .2994 .5361

Experimental gestures produced .5488 .5091 .5381

Laboratory Gestures produced

spontaneously in free-play condition .6585 .8088 .0656

Gestures imitated in language- neutral condition .7987 -.2036 .8705

Age .6323 .3926 .6915


Although the relation between comprehension and gesture is quite robust, appearing in both the observational and parental report data, some version of the parallelism hypothesis is still needed to account for the independent relation that holds between gesture and expressive language. This was made particularly clear in the contrast between the respective comprehension and production group analyses. Comprehension level inter- acted with the language support manipulation; production level did not. Children with high expressive vocabularies produced more gestural imitations in the experiment in all three language support conditions.

The same conclusion falls out of the factor analyses in Study 1 and Study 2. Two significant factors emerged in both these studies, reflecting a dissociation between comprehension and production in this age range. Because the factor scores are made up of different ingredients in Study 1 and Study 2, the two analyses may be telling slightly different stories. But the similarities are interesting, and they offer us some possible directions for future research.

In both studies, we argued that the Comprehension factor reflects developments in symbolic/conceptual content. In Study 1, this factor was associated with deictic gestures and enactive naming (i.e., gestures that are used to recognize, explore, and communicate about a world of familiar objects). In Study 2, the factor was again associated with measures of enactive naming, in free play and parental report. These measures all tap into the spontaneous use of gesture under relatively naturalistic condi- t ions-wi th realistic objects and with supporting gestural and vocal activity provided by the parent.

Both studies also yielded a second factor, associated with variance in word production. In Study l, this factor was associated with routines that make reference to nothing but themselves (e.g., "pattycake," "bye-bye"), although it also received some contribution from object-associated gestures. In Study 2, this factor was associated with "decontextualized" gesture--action schemes produced without support from the target object, independent of the adult's accompanying narration. Parental report loaded on both factors, in both studies, suggesting that the gesture inventory picks up variance in the production of recognitory gestures under a wide variety of eliciting conditions.

To interpret these dissociations correctly, we must remember that factor analysis maximizes orthogonality. Hence, the Pro- duction factor in both studies reflects those aspects of expressive language that are not shared by comprehension--presumably some kind of performance variable. There are (at least) three possible interpretations of this independent link between word production and aspects of production in the gestural domain:

1. Imitativeness. In the linguistic domain, some children may have receptive vocabularies far beyond their expressive speech because they are "cautious," unwilling to attempt reproduction of adult speech until they are absolutely certain what it means. The same children might be reluctant to imitate an adult gesture out of context, without additional cues from language or the referent object. Other children may be willing to imitate an adult model in either modality, whether they under- stand it or not. Differences in "propensity to imitate" might in turn reflect several different factors: temperament (e.g., shy-

ness), aspects of the mother-child relationship (e.g., whether or not the parents encourage and reward imitation), and cognitive style (i.e., whatever factors are responsible for the curvilinear relation between comprehension and imitation observed in Study 2).

2. Conceptual progress. Production of both gestures and words for common objects may be based in part on advances in symbolic understanding above and beyond the level required for comprehension--a different cognitive system or, alternatively, a higher level of sophistication within the same symbolic system.

3. Motor planning. Progress in gestural and vocal production in the 12-16-month age range may be based on some kind of shared articulatory/motor development for which comprehension is a necessary but not sufficient condition.

We cannot decide among these interpretations at this time. They are not mutually exclusive, and they are all compatible with the parallelism hypothesis. However, one final counter to parallelism could still be entertained: Perhaps children with high vocabularies perform better on abstract symbolic play tasks because they are talking to themselves. That is, the infant may use covert production (rather than comprehension) as an aid to his or her gestural activity. We certainly cannot rule out this possibility because it may account for some of the advantage that the children with larger expressive vocabularies displayed in our task.

However, there are reasons to believe that covert speech plays a minimal role in this age range. First, very few children produced any overt object labels in this experimental situation. Second, descriptive statistics from the parental report and observations in the laboratory both suggest that gestural production is developing ahead of expressive language. This fact makes it unlikely that children produce gestures by first retrieving an associated word, using that covert or overt word as a guide to gestural production. Third, children at the earliest stages of symbol development tend not to have a large number of overlap- ping words and gestures in their repertoires (Volterra et al., 1979). If the child has a word for an object, he or she is slightly less likely to have a corresponding gesture; conversely, if the child has a gesture for a given object, he or she is initially somewhat less likely to acquire or make use of the corresponding word. This trend is compatible with an argument first raised in the bilingualism literature by Volterra and Taeschner (1977): Children in the earliest stages of lexical development tend to avoid assigning two words to the same referent, so that words from their respective languages lie in complementary distribu- tion with few if any translatable pairs. The rule seems to be "one referent, one symbol." Slobin (1985) also reported this effort to keep things simple in the early stages of grammatical development. He described it as the principle of "one form, one function." Taken together, these findings suggest that covert linguistic production is probably not going on while a "gestural name" is being produced, at least not in the early stages of symbol development.

At some point in development, it is both possible and likely that language "wraps back around" to provide support for symbolic play activity, through comprehension mediation (which we have demonstrated), and possibly through covert or overt language production (a point for further investigation--cf. Vy-


gotsky, 1967). There is, nevertheless, still ample evidence for some form of parallelism in the development o f language and gesture, This finding is impor tant for those practitioners who would like to use the child 's level o f functioning in a nonlinguistic domain as an aid in the interpretation o f language delays (Leonard, 1988; Rice, 1983; Thai & Bates, 1988a, 1988b).

Given the complexity of our findings, such assessments must be carried out with extreme caution. Results may vary, depending on the conditions under which gesture is assessed (i.e., with or without perceptual support from the object, and with or without either gestural or vocal cuing from an adult). Also, results will most certainly vary depending on whether the investigator is interested in receptive or expressive language development. As we have seen, comprehension and production o f language can be dissociated to a remarkable degree in normally developing children (Bates et al., 1987) and in children who are delayed or impaired in language (Tallal, 1987; T h a l & Bates, 1988a). Our results suggest that the same dissociation is re- flected in the relation between language and gesture. There are at present no convincing explanations for this dissociation in- side or outside o f the language domain. However, it is possible that further comparisons o f language and gesture may help to solve the problem.

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Appendix

Object Words and Gestures Used in Experiment

Word Gesture

% of children % of children % of children % of children reported to reported to reported to producing

produce comprehend produce gesture in gesture word word experiment

Cup Baby Phone Spoon

Comb Car Toothbrush

Hat Flower Soap Dog Airplane

Drink with head back, cupped hand 95 62 0 63 Hug with rocking motion 90 71 38 12 Put to ear 88 71 2 29 Put to mouth (open and close 86 58 2 39

mouth, hand to side of mouth) Comb hair 86 71 0 37 Back and forth motion on table 84 67 24 37 Brush teeth with horizontal back 61 56 0 49

and forth motion Put on top of head 54 40 7 22 Put to nose and sniff 45 53 11 37 Wash hands 22 29 4 17 Hop across table 18 82 69 44 Back and forth motion in the air 9 38 7 17

Received M a r c h 11, 1988 Revision received M a r c h 22, 1989

Accepted M a r c h 23, 1989 •

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