Infant Behavior & Development 37 (2014) 235–247

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Infant Behavior and Development

Beside the point: Mothers’ head nodding and shaking gestures during parent–child play夽 Maria Fusaro a,∗ , Claire D. Vallotton b , Paul L. Harris c a b c

San Jose State University, United States Michigan State University, United States Harvard Graduate School of Education, United States

a r t i c l e

i n f o

Article history: Received 9 August 2013 Received in revised form 6 December 2013 Accepted 24 January 2014 Available online 15 March 2014

Keywords: Gesture Parent–child interaction Social context Social learning Pragmatics Language input

a b s t r a c t Understanding the context for children’s social learning and language acquisition requires consideration of caregivers’ multi-modal (speech, gesture) messages. Though young children can interpret both manual and head gestures, little research has examined the communicative input that children receive via parents’ head gestures. We longitudinally examined the frequency and communicative functions of mothers’ head nodding and head shaking gestures during laboratory play sessions for 32 mother–child dyads, when the children were 14, 20, and 30 months of age. The majority of mothers produced head nods more frequently than head shakes. Both gestures contributed to mothers’ verbal attempts at behavior regulation and dialog. Mothers’ head nods primarily conveyed agreement with, and attentiveness to, children’s utterances, and accompanied affirmative statements and yes/no questions. Mothers’ head shakes primarily conveyed prohibitions and statements with negations. Changes over time appeared to reflect corresponding developmental changes in social and communicative dimensions of caregiver–child interaction. Directions for future research are discussed regarding the role of head gesture input in socialization and in supporting language development. © 2014 Elsevier Inc. All rights reserved.

1. Introduction In the first years of life, infants encounter and interpret communicative signals in both verbal and non-verbal forms. Understanding the context for children’s social learning and language acquisition requires consideration of such multimodal (speech, gesture) messages. A rich body of research exists on children’s use and interpretation of pointing gestures (see Tomasello, Carpenter, & Liszkowski, 2007). Infants typically begin using this deictic gesture around 11–12 months (Carpenter, Nagell, & Tomasello, 1998). A number of studies have also elucidated the information that infants can gain from others’ pointing gestures, such as the location of hidden objects (Behne, Liszkowski, Carpenter & Tomasello, 2012; Gliga & Csibra, 2009).

夽 This manuscript is based on data also used in a doctoral dissertation submitted by Maria Fusaro to Harvard Graduate School of Education. The authors wish to thank Barbara A. Pan and Catherine Snow for access to the CHILDES New England Sample parent–child play videos, and Kurt Fischer for comments on a previous version of this manuscript. We also acknowledge the research assistants who contributed to data preparation and coding: Adrian Dede, Julia Hayden, Lindsay Fryer, Dayna Johnson, Sarah Lipson and Rose Wongsarnpigoon. ∗ Corresponding author at: Department of Child and Adolescent Development, San Jose State University, One Washington Square, San Jose, CA 951920075, United States, Tel.: +1 4089243740. E-mail address: [email protected] (M. Fusaro). 0163-6383/$ – see front matter © 2014 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.infbeh.2014.01.006

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Interactions involving additional gestures, beyond pointing, may also be foundational for the child’s social learning. The current study seeks to expand our understanding of gestural input by considering the role of adults’ head nodding and head shaking gestures, subsequently referred to as head gestures, in their messages to young children. We focus on these gestures because, although they are ubiquitous in adult–adult communication, little empirical work exists on their frequency in caregiver–child interaction or the role they play in those interactions. Existing research suggests that head gestures enter into children’s communicative repertoire in the second year of life. In terms of head gesture production, infants in the U.S. typically begin to shake their heads no by around 12 months, and nod their heads yes by 14 months, some months earlier than the typical emergence of the corresponding verbal forms “no” (15 mos.) and “yes” (19 mos.; Fenson et al., 1994). Children use head gestures to convey various communicative intentions, including refusal and answering questions (Carpenter, Mastergeorge, & Coggins, 1983; Crais, Douglas, & Campbell, 2004; Fusaro, Harris, & Pan, 2012). As an initial exploration of children’s comprehension of head gestures, Fusaro and Harris (2013) tested 18- and 24-month-olds’ use of an adult’s head gestures to disambiguate competing pieces of information in objectlabeling and object hiding tasks. Children were invited to choose an object or a hiding location on the basis of an adult’s head nods or head shakes. These gestures were produced in response to the assertions or yes/no questions of an interlocutor who proposed either the correct or incorrect choice. The 24-month-olds readily used the adult’s head nodding and head shaking gestures to identify the correct object and hiding location. Further, the 18-month-olds showed some sensitivity to head gestures when they were responses to a speaker’s yes/no questions about hiding locations. Previous observational studies of mothers’ gestural input have not focused on head gestures specifically. Instead, these have been grouped with other gestures, like waving hello and goodbye, into a broader category of conventional gestures (Bekken, 1989; Iverson, Capirci, Longobardi & Caselli, 1999; Iverson, Capirci, Volterra & Goldin-Meadow, 2008; Iverson & Goldin-Meadow, 2005; Rowe, Özc¸aliskan, & Goldin-Meadow, 2008; Shatz, 1982). These studies provide some insight into the frequency of caregivers’ gesture use. Based on observations of mother–child dyads during the child’s second year of life, about 10–15% of US and Italian mothers’ communicative messages to young children include some kind of gesture (Bekken, 1989; Iverson et al., 1999; Rowe et al., 2008; Shatz, 1982). Mothers use gestures in tandem with speech more often than in isolation (Iverson et al., 1999; Rowe et al., 2008). Iverson et al. (1999) examined twelve Italian caregivers’ use of a broad range of gestures with their children at 16 and 20 months of age. Dyads were observed in their homes, playing with familiar objects and with the experimenter’s standard set of toys, as well as during snack or meal time. Mothers’ head gestures were grouped with other conventional gestures for analysis (e.g., turning the palms up for “all-gone,” finger to cheek for “good”). On average, mothers used conventional gestures approximately 30 times per 45-min observation at both time points. Although a great deal of variability among mothers was detected, the relative frequency of conventional gesture use did not differ significantly between the 16- and 20-month observation periods. The functions of mothers’ gestures were examined at a general level. Most often, mothers’ gestures served to reinforce the mother’s verbal message. Gestures sometimes disambiguated a message (e.g., pointing to a particular location while saying “that one”). Rarely, they added new information to the verbal utterance (e.g., pointing to a toy while saying “pretty”). This broad description provides insight into mother’s gestural communication with infants, but it does not elucidate potential differences in the relative frequency of caregiver head gestures over time, and the meaning behind these gestures in parent–child interaction. Like other conventional gestures, head gestures used within dialog can convey meanings that may be roughly translated into an equivalent verbal expression (e.g., “Yes,” “No,” “That’s right”). Given these features, head gestures can be considered as equivalent to speech acts, and their illocutionary force can be analyzed as such (Austin, 1962; Guidetti, 2000). In particular, head gestures can be used to convey messages such as willingness or refusal to carry out a requested behavior, agreement or disagreement with substantive claims, as well as answers to yes/no questions (Fusaro et al., 2012; Guidetti, 2000, 2005; Kendon, 2002). It is possible that adults support the development of children’s communication by modeling these messages with their own visible head gestures. Caregivers may also use head gestures, in tandem with vocal input, to guide children’s behavior, as a means for socialization. For example, in response to a child’s disruptive use of a toy, a caregiver might lower her prosody, tell the child to “stop,” and simultaneously shake her head “no” and remove the toy. Importantly, the role of parents’ head gestures might change over time, as children’s social and language skills develop from infancy through early childhood. More research is needed on head gesture input and function to begin to address these questions. Understanding the frequency and role of head gestures in communication and social learning requires a fine-grained analysis of the gestural environment. The current study describes mothers’ spontaneous use of head gestures with their young children in laboratory-based play sessions. To examine how caregivers’ messages to children might change over time, head gesture production was observed longitudinally at three points during early childhood, based on videotaped interactions of mother–child dyads from the New England corpus of the Child Language Data Exchange System (Pan, Imbens-Bailey, Winner, & Snow, 1996; Snow, Pan, Imbens-Bailey, & Herman, 1996). The primary research questions were:

1. How often do mothers use head gestures during play interactions with their young children in the second and third years of life? Does the frequency of mothers’ head gesture production differ when children are 14, 20 and 30 months of age? 2. For what communicative purposes do mothers use head gestures with their young children? Do mothers use head gestures for similar functions when children are 14, 20, and 30 months of age?

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Answers to these questions will provide new insight into a potentially significant but understudied component of the young child’s social and communication environment. 2. Method 2.1. Participants Participants included a subset of parent–child dyads from the New England corpus of the Child Language Data Exchange System (Pan et al., 1996; Snow et al., 1996). Data were originally collected from 52 dyads longitudinally, in the 1980s, when children were approximately 14, 20, and 32 months. A subset of 32 dyads (n = 15 girls, n = 17 boys) was used for the current study, including children with all three waves of video and transcript data, and who participated with the same parent (i.e., mother) at each time point. The average child age in months was 14.18 (SD = .25) at Time 1, 20.01 (SD = .55) at Time 2, and 30.69 (SD = 1.65) at Time 3. The original sample, drawn from English-speaking, predominantly White families, included equal proportions of male and female children, of lower-middle and upper-middle class households (MacWhinney, 2000). Children with indications of medical or other developmental problems were excluded. 2.2. Procedure Parent–child dyads were videotaped during three semi-structured play sessions in a laboratory setting. At 14 and 20 months, the sessions began with a 5-min warm-up period, during which several standard toys were available for free-play (e.g., small football, squeaky duck, book, jack-in-the-box, toy car). The parent and child then played with four standard toys, one at a time: a ball, a cloth for peek-a-boo, crayons and paper, and a book. At 30 months, the warm-up period was omitted, and the toys included a book, hand puppets, crayons and paper, and a toy house. At each time point, parents were instructed to use the toys, each contained within a separate box, in succession for a total of about 10 min. Within the session, dyads were free to play with each item for as long as they chose. Sessions were terminated after the parent had tried to engage the child in all four activities. A video camera in the corner of the room (Time 1 and 2) or behind a one-way mirror (Time 3) recorded the caregiver and child’s behaviors. Description of the frequency of mothers’ gesturing was based on mother on-screen time, yielding observations of an average duration of 13:52 (SD = 4:01) at Time 1, 11:34 (SD = 3:15) at Time 2, and 10:41 (SD = 3:08) at Time 3. 2.3. Transcription and coding 2.3.1. Parent–child language Parent and child utterances during the play interactions were previously transcribed using the CHAT conventions of the Child Language Data Exchange System (MacWhinney, 2000; MacWhinney & Snow, 1985, 1990). Transcripts are publicly available through the CHILDES system, and videos are archived at the Harvard Graduate School of Education. The original investigators of the New England data transcribed and segmented parent and child communication into utterances, which were then coded according to the Inventory of Communicative Acts–Abridged (INCA-A; Ninio, Snow, Pan, & Rollins, 1994; Ninio, Wheeler, Snow, Pan, & Rollins, 1991). This inventory, modified from a more elaborate system (Ninio & Wheeler, 1984), is designed to categorize interactions between parents and young children. Communicative acts are coded both for the type of ongoing communicative interchange in which they are embedded (e.g., discussing a joint focus of attention), and for the particular type of speech act produced (e.g., asking a yes/no question). 2.3.2. Identifying mother head gestures For the current study, all instances of maternal head gestures were identified from the videotapes. Head gestures were defined as at least one up-down (nod) or left-right (shake) movement of the head at the neck. Exceptions were made for the following types of head movements: those accompanied by singing or music, those that were used to indicate a particular location (e.g., motioning with the head while saying “Put it over there”), and artifacts of whole-body movement. Ten percent (10%) of play sessions were dual-coded to assess inter-coder agreement. Previous observational studies of gesture production (e.g., Capirci, Iverson, Pizzuto, & Volterra, 1996; Guidetti, 2005) calculate percent agreement based on a method described by Sears, Rau, and Alpert (1965) and Kratochwill and Wetzel (1977); the number of gesture instances identified in common by the two coders is doubled and then divided by the sum of the number of instances captured by each coder. In the current study, this percent agreement for identifying gestures was 88%. Disagreements were resolved by discussion between the coders. 2.3.3. Coding mother head gestures From video, head gestures were categorized in terms of the type of speech act they expressed. To make connections to previous studies, we also coded the relationship between gesture and speech, and the occurrence of an imitation of the child’s preceding gesture. Speech act types conveyed by head gestures included a subset of categories from the INCA-A (Ninio et al., 1994), such as agree with proposition expressed by child, and prohibit/forbid/protest child’s performance of an act. Table 1 summarizes the

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Table 1 Descriptions of speech act classifications associated with mothers’ head gestures, and average frequency (percent) of mothers’ gestures that conveyed each function, collapsing across mothers and time points.

Both head nods and head shakes State; Make a declarative statement ST SA: Answer a wh-question by a statement TX: Read/recite written text aloud

Average % of head nods

Average % of head shakes

12.4

27.6

YQ

Ask a Yes/No question (gesture is contemporaneous response) RQ: Yes/No question about child’s wishes and intentions which functions as a suggestion (e.g., “Do you want to. . .” “Can you. . .”)

10.7

13.4

RT

Repeat/imitate child’s utterance

4.2

4.4

32.2

1.0

Primarily head nodding speech acts Agree with proposition expressed by child (e.g., “Yeah, picture”) AP CT: Correct, provide correct verbal form in place of erroneous one; (e.g., “Picture” in response to child’s word approximation) AC

Answer calls; Show attentiveness to communications XA: Exhibit attentiveness to child, when child has not made a bid for attention

18.5

0.0

RP

Request/propose/suggest action for child, or for child and parent (e.g., “Come sit over here;” “Keep turning it”). SS: Signal to start performing an act, e.g., to run or roll a ball. Pace performance of acts by child (e.g., “Go ahead.”) CS: Counter suggestion; an indirect refusal (e.g., “You write with it.”) PD: Promise (e.g., to do an act later)

8.2

0.6

AB

Approve of appropriate behavior. Express positive evaluation of child’s or parent’s acts PM: Praise for motor acts, i.e., for nonverbal behavior

4.5

0.0

AA

Answer in the affirmative to child’s yes/no question

2.3

0.0

0.5

35.8

Primarily head shaking speech acts Prohibit/forbid/protest child’s performance of an act PF ED: Exclaim in disapproval WD: Warn of danger DS: Disapprove, scold, protest disruptive behavior. Express negative evaluation of child’s behavior as inappropriate GR: Give reason; justify a request for action, refusal, or prohibition DW

Disagree with proposition expressed by child

0.1

9.9

RD

Refuse to carry out act requested or proposed by child

0.0

5.6

observed gesture functions and is arranged into three sections; first those speech acts encoded by both types of head gestures, then those that were primarily associated with head nods, and finally those primarily associated with head shakes. Given the large number of functions expressed, some speech act types are combined under a primary category for display purposes. For example, statements initiated by the mother (ST), made in response to the child’s wh-question (SA), and read from book text (TX), are grouped under the category Statements. Only categories that comprised at least two percent of either observed head nods or head shakes are displayed. As described above, mothers’ utterances, some of which were accompanied by head gestures, already had speech act codes assigned to them. The same codes were applied to the gestures, when the gesture reinforced the verbal speech. For example, a head nod could accompany the mother’s verbal expression of agreement with the child’s preceding statement; the gesture was likewise coded as expressing agreement. If the speech act categorization of the utterance differed from that of the gesture, the one that applied to the gesture was assigned. For example, if the mother simultaneously read from a book while nodding to show attentiveness to the child’s utterance, the attentiveness code was assigned to the gesture. If the gesture spanned two utterances, the code from the first utterance was used for the analysis. Finally, throughout this analysis, The INCA-A categories of agreement and correcting verbal form codes were combined into a single category. This exception was due to ambiguity in coding mothers’ expression of agreement with children’s utterances, when those utterances were word approximations; for example, a child utters “Ba” and the mother nods while saying, “Yes, that’s a ball.” Codes for the relationship between the gesture and the accompanying speech included reinforce/intensify the verbal message, mitigate the force of a verbal message (as in a head shake conveying uncertainty about an accompanying statement), supplement speech that conveys a different meaning (as in a head shake that accompanied the mother’s neutral yes/no question, as if she is answering her own question), and substitution for speech when there was no overlap between the gesture and an utterance. Finally, gestures were coded as imitations when they occurred within three seconds of the child’s preceding gesture.

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Table 2 Descriptive statistics for the frequency of mother gestures per 10 min, by gesture type and child age (N = 32 mothers). Child age

N gestures

Frequency per 10 min M

Mdn

SD

Nods

14 mos. 20 mos. 30 mos.

201 211 172

4.0 5.8 4.9

3.5 4.2 3.3

3.70 5.17 5.01

Shakes

14 mos. 20 mos. 30 mos.

109 81 46

2.5 2.5 1.3

2.1 1.5 1.2

2.40 3.45 1.12

A random sample of 15% of maternal head gestures was double-coded to assess the reliability of mother gesture coding. First, we assessed the extent to which coders agreed upon the speech act category (e.g., prohibit/forbid/protest child’s performance of an act) that captured the meaning of the gesture. The value for Cohen’s kappa, which takes into account chance agreement between coders, was .70, which represents substantial agreement (Landis & Koch, 1977). For the coding of the relationship between gesture and speech (i.e., reinforce, mitigate, supplement, or substitute), the value for Cohen’s kappa was .76. Reliability could not be assessed for the coding of mothers’ gestures as imitations of the child’s gesture, because, as described next, these instances were rare. 3. Results 3.1. Frequency of head gestures To examine the frequency of maternal head gestures, Table 2 presents descriptive statistics for head gesture frequencies, by gesture type and child age. Because the duration of sessions was variable, frequencies are presented as the number of observed gestures per 10 min (10 min intervals were chosen for ease of interpretation). Mean frequencies for head nodding varied between 4.0 and 5.8 per 10 min at the three time points. This frequency translates to roughly one head nod every 2–2.5 min, on average. For head shakes, the mean frequency at each time point ranged from 1.3 to 2.5, translating to roughly one gesture every 4–7.5 min. Almost all of the mothers’ gestures were produced spontaneously, as opposed to being imitations of the child’s gestures; in total, 3.2% of mothers’ head gestures were imitations of the child’s preceding gesture. Fig. 1 displays the distribution of mothers’ gesturing frequencies, by child age and gesture type. Horizontal bars indicate median frequencies, shaded boxes represent the 25th to 75th percentile range, and open circles and asterisks represent outliers by observation number. Mothers varied greatly in the frequency with which they used head gestures. At each time point, some mothers produced either no head nods or no head shakes, while others used a head gesture more than ten times per 10 min. At each observation, average head nodding frequencies were higher than head shaking frequencies. Non-parametric tests were used to compare frequencies, because these values were not normally distributed. Wilcoxon Signed-Rank Tests (2-tailed), confirmed that these differences were significant at each time point (Time 1: z = 2.19, p = .029; Time 2: z = 3.14, p = .002; Time 3: z = 3.70, p < 001). Analysis of individual patterns of gesture use revealed that 59% of mothers used more head nods than shakes at Time 1, 72% did so at Time 2, and 63% at Time 3. Collapsing across the three sessions, 88% of mothers (28 of 32) produced more head nods than head shakes, again suggesting that in most cases, mothers’ nods outnumbered their head shakes. Thus, during this age range, and in this dyadic play context, mothers produced more head nods than head shakes, despite the likely need to regulate the child’s behavior via prohibitions during this period of development. Next, for each gesture, frequencies were compared across time points, again using Wilcoxon Signed-Rank tests (2-tailed). As seen in Fig. 1, head nodding frequencies generally peaked at the second time point; 20-month nodding frequencies were significantly higher than 14-month frequencies (z = 2.02, p = .044) though non-significantly higher than 30-month frequencies (z = 1.63, p = .104). In contrast, head shaking rates generally decreased over time; 30-month rates were significantly lower than 14-month rates (z = −2.71, p = .007), and non-significantly lower than 20-month rates (z = −1.57, p = .117).1 Finally, we examined two different aspects of inter-individual stability in head gesture frequency.2 First, at each time point, we examined the correlation between mothers’ frequency of head nods and head shakes. Because our data are frequency count data, and thus exhibit the negative skew typical of frequency data, we used Spearman’s Rank Order correlations rather than Pearson correlations. There were no significant inter-individual correlations between nods and shakes at any of the three waves. Second, we tested the stability of inter-individual differences in the frequency of mothers’ head shaking and head nodding, separately, over time, again using Spearman’s Rank Order correlations. Table 3 provides the 2-tailed Spearman correlations between mothers’ frequency of head gestures at each time. As seen in Table 3, there is more inter-individual

1 2

Paired-sample t-tests comparing mean frequency levels by age and gesture type yielded a similar pattern of findings as the non-parametric tests. We thank an anonymous reviewer for this suggested analysis.

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Fig. 1. Distribution of mother gesture frequencies, by child age and gesture type (N = 32).

Table 3 Results of Spearman’s Rank Order correlations (2-tailed) testing inter-individual stability in the frequency of mothers’ head gestures through children’s second year of life. Head shakes

Time 1 Time 2 ∼ * **

Head nods

Time 2

Time 3

Time 2

Time 3

0.226 –

0.341∼ 0.319∼

0.384* –

0.576** 0.653**

p < .10. p < .05. p < .01.

stability in mothers’ head nodding than head shaking frequency. Nonparametric rank order correlations were small and significant only at the p < .10 level for head shaking, but they were moderate to large for head nodding. Interpreting such frequency-related findings requires consideration of why mothers were using these gestures. We turn next to the results for the relationship between gesture and speech, to provide a context for the findings with respect to our second research question concerning the communicative function of head gestures.

3.2. Relationship between gesture and speech Consistent with previous research (Iverson et al., 1999), most of mothers’ head gestures, 98% of overall instances, occurred with speech. Overall, 2.7% of head nods and only one instance of a head shake (.4% of headshakes) substituted for speech (i.e., occurred in isolation). Most gestures reinforced or intensified a verbal speech act (overall = 91.6%; nods = 91.6%; shakes = 91.5%), whereas 4.9% supplemented (nods = 5.3%; shakes = 3.8%) and 1.5% mitigated the utterance (nods = 0.3%; shakes = 4.2%). Examples of mitigating and supplemental gestures are discussed below, as part of the description of each relevant gesture function.

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*

Agree/Correct

241

*

Show Attentiveness

Statement

Ask a Yes/No Question Suggest an activity Approve of Behavior

*

14 months

*

20 months 32 months

Repeat

Answer Yes 0

20

40

60

Average Percent of Maternal Head Nods

* p < .05; Significant Bonferroni post-hoc comparisons within each category Fig. 2. Average percent of mothers’ head nods used for eight primary speech act categories, by child age.

3.3. Communicative function of head gestures To address the second research question, head gesture functions are described in this section. In Table 1, values in the second and third column represent the average percentage of mothers’ head nods and average percentage of mothers’ head shakes used to convey each group of speech acts, collapsing across time points. Note that sample sizes are variable, as mothers who did not use one or both head gestures at a given time point are excluded in the relevant calculations. As shown in the table, the majority of head nods and headshakes fell into a small number of primary categories. The most common use of head nods was to convey agreement with the child’s propositions. Most commonly after this, head nods expressed attentiveness to the child, accompanied declarative statements, and were produced as a contemporaneous response to the mother’s own yes/no question. Overall, mothers’ head shakes were predominantly aimed at prohibiting the child’s behavior, and accompanied declarative statements. Head shakes as responses to the mother’s own contemporaneous yes/no questions were also relatively common. To consider how mothers’ use of head gestures differed across time points, Figs. 2 and 3 display the average percent of head nodding and shaking gestures that reflect each speech act category by child age. As in Table 1, combined categories are displayed and used for analyses. These results are reported next, by complementary categories (e.g., agreement/disagreement). To examine the statistical significance of differences, two types of analyses are reported. These include comparisons of the mean percentages over time for a given function and gesture type (one-way repeated measures ANOVA), and comparisons across gesture types for complementary functions, for a given time point (paired-samples t-tests).3 3.3.1. Agreement and disagreement At each time point, mothers nodded their heads to agree or disagree with a proposition offered by their child. Mothers’ agreement (AP) responses often referred to children’s labels for objects in the playroom and pictures in storybooks. Mothers

3 In the following sections, we use ANOVA analyses when feasible. Paired t-tests are used to maximize the number of cases included in pair-wise comparisons. Given the exploratory nature of these analyses, and the use of repeated tests, in particular, there is a need for caution in the interpretation of statistical significance.

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***

***

Prohibition

Statement

Y/N Question

14 months

Disagreement

20 months 32 months Refusal

Repeat

0

20

40

60

80

Average Percent of Maternal Head Shakes

*** p < .001; Significant Bonferroni post-hoc comparisons within each category Fig. 3. Average percent of mothers’ head shakes used for six primary speech act categories, by child age.

also confirmed correct sounds associated with animals, and single descriptive words, like “dirty” or “baby’s,” and, at 30 months, multi-word phrases (e.g., “brushing his teeth” “he might wake up”). This category also includes cases at each time point when mothers nodded while providing a corrected verbal form (CT) in place of an erroneous one offered by the child. For example, mothers would nod when children either approximated a word form (e.g., saying “Ba” for ball) or provided an imperfect response to a labeling probe (e.g., saying “Shorts” for overalls). Together, these agreement messages represented the highest average proportion of head nods when children were 20 months of age (M = 34.2, SD = 33.5), and 30 months (M = 34.8, SD = 32.0). A repeated measures ANOVA determined that the mean proportion of head nods used for agreement differed significantly between time points (F(2, 42) = 4.39, p = .019). Post hoc tests using the Bonferroni correction confirmed that the 14-month mean (M = 13.1, SD = 20.9) was significantly lower than the mean at 20 months (p = .046) and 30 months (p = .030). As with agreement, when mothers disagreed with a proposition (DW), the content of that proposition was often a verbal label, such as when the child referred to a picture of a bear as a dog. Other disagreements referred to children’s incorrect animal noises, use of objects, and color words. The average proportion of mothers’ head shakes used to convey disagreement was small at Time 1 (2.0%) but became more frequent at Time 2 (7.2%) and Time 3 (18.4%). However, a repeated measures ANOVA confirmed that these differences were not statistically significant. Overall, the average percent of head nods expressing agreement was significantly higher than the average percent of head shakes that conveyed disagreement with the child’s propositions (paired t-test, t(30) = 4.73, p < .001). Paired-sample t-tests confirmed that this difference was statistically significant at Time 1 (t(21) = 2.54, p = .019, d = .54) and Time 2 (t(22) = 3.25, p = .004, d = .68) and marginally so at Time 3 (t(20) = 1.87, p = .076, d = .41). 3.3.2. Regulating the child’s behavior One of the most frequent uses of mothers’ head shakes was to prohibit inappropriate or forbidden behavior (PF). Mothers conveyed disapproval by explicitly prohibiting the child’s ongoing behavior, by warning children of danger (WD e.g., “You’re gonna fall.”) and by giving reasons for a prohibition (GR e.g., “It [crayon] doesn’t taste good”). Mothers used head shakes while prohibiting inappropriate uses of crayons, such as putting crayons in the mouth, drawing on surfaces other than paper, and breaking crayons. Other attempts to regulate the child’s behavior with head shakes typically included discouraging the child from approaching undesirable objects in the testing room (e.g., power outlet, trash can, experimenter’s desk, mother’s bag). Prohibitions were most frequent when children were 14 months old; on average, 58.4% (SD = 39.5) of mothers’ head shakes at Time 1 served this purpose. At 20 months of age, an average of 13.5% (SD = 17.4) of head shakes were aimed at prohibiting behavior, and by 30 months, this proportion dropped to 2.5% (SD = 8.5). A repeated measures ANOVA, with a Greenhouse–Geisser correction applied for a violation of the sphericity condition, confirmed that the percentage of

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headshakes used for prohibitions differed significantly over time (F(1.24, 18.63) = 32.94, p < .001). Post hoc tests using the Bonferroni correction revealed that the percentage at Time 1 was significantly higher than the percentage at Time 2 (p < .001) and at Time 3 (p < .001), while the difference between Time 2 and 3 was non-significant. Conversely, mothers used head nods to express approval when children demonstrated desirable behaviors (AB) and motor acts (PM). Mothers often nodded when children appropriately used a crayon to make marks on paper and, at Time 1 and 2 which included the warm-up session, when children attempted to operate a challenging toy (i.e., a jack-in-the-box). At Time 3, a small number of nods were used to praise children’s appropriate use of hand puppets and items in the toy house. At Time 1, an average of 11.9% (SD = 17.6) of head nods were used for these related purposes, more than at later time points (Time 2: M = 1.8%, SD = 5.3; Time 3: M = 2.1%, SD = 4.6).4 A repeated measures ANOVA, with a Greenhouse–Geisser correction, revealed that the percentage of head nods used for approval differed significantly over time (F(1.27, 26.68) = 7.25, p = .008. Bonferroni post hoc tests confirmed that the percentage at Time 1 was significantly higher than the percentage at Time 2 (p = .019) and at Time 3 (p = .047), while the difference between Time 2 and 3 was non-significant. Based on paired-sample t-tests, the average percent of head shakes conveying prohibition-related messages exceeded the percent of head nods that expressed approval for behaviors and motor acts at Time 1 (t(21) = 6.05 p < .001, d = 1.29) and Time 2 (t(22) = 2.78 p = .011, d = .58). By Time 3, the use of head gestures to convey approval and disapproval did not differ in frequency from each other (t(20) = .05, ns, d = .01). 3.3.3. Showing attentiveness to the child At each time point, mothers’ head nods were used to show attentiveness to the child. A mother’s nod and content-less vocalization (e.g., mhmm) signaled that she was paying attention. For example, a child showed his mother a toy car, and in response she said “Yeah” and nodded. These cases included answering the child’s bids for attention (AC) or, at Time 1 and 2, demonstrating attentiveness even in the absence of a bid for attention (XA). Combining these categories, an average of 22.6% (SD = 27.8) of mothers’ head nods at Time 1, 17.4% (SD = 22.8) at Time 2, and 11.2% (SD = 13.9) at Time 3 were used to show attentiveness. A repeated measures ANOVA confirmed that this decrease over time was not statistically significant. Most of the few head nods that mothers produced without speech also fell into this category. Further, mothers occasionally used a head nod to acknowledge the child, but as a supplement to a different verbal act (e.g., while reading from a book, or while asking a follow-up question). Another way mothers demonstrated attentiveness was by repeating the child’s verbal utterances with an accompanying head gesture (RT: nods: Time 1: 2.5% (SD = 10.1), Time 2: 1.6% (SD = 5.6), Time 3: 4.8% (SD = 12.1); shakes: Time 1: 1.0% (SD = 4.9), Time 2: 2.5% (SD = 8.6), Time 3: 6.1% (SD = 15.1). For instance, a mother would repeat the child’s utterance of “No” or “I don’t know” while shaking her head, without evidence of an additional communicative intent. These cases, along with content-free utterances, provided the child with an acknowledgment that the mother was attentive to his or her behavior. 3.3.4. Responding to children’s questions and suggestions Mothers’ head gestures were sometimes part of affirmative or negative verbal responses to their child’s yes/no questions. Nods for “yes” (AA) were not common at 14 months (M = 1.0%, SD = 4.9) or 20 months (M = 1.5%, SD = 5.1), but became slightly, though non-significantly, more common at 30 months (M = 4.4%, SD = 11.4). Only one instance of shaking the head “No” in response to a child’s question was observed across all mothers at each time point. Similarly, only a few head nods were used as part of mothers’ agreement to do something requested or proposed by the child, such as in response to the child’s request for mother to draw a dog (AD: overall average percent = 1.1%). Similarly, shaking the head to indicate a refusal to do a proposed act (RD) was rare at Time 1 (M = .8%, SD = 3.9), though comprised a non-significantly higher average of 6.4% (SD = 21.0) and 4.3% (SD = 20.9) of mothers’ head shakes at Time 2 and 3, respectively (e.g., mother refuses to open her bag to get child a snack, by shaking her head and saying “uh-uh.”). The frequency with which maternal gestures served as a response to children’s questions and statements is constrained by children’s developing ability to ask yes/no questions and to make requests of parents to perform an act. Indeed, some of the yes/no questions to which mothers responded were one-word utterances with rising intonation (e.g., “Daddy?”, “Blue?”, “Mine?”). At 30 months, mothers responded with head nods to a small number of full-fledged yes/no questions like “That way?” (verifying the orientation of the box cover) and “Is that your paper?” 3.3.5. Gesturing while asking a yes/no question While head gestures in response to children’s questions were infrequent, mothers often used head gestures while asking their own Yes/No questions (YQ: nods: Time 1: (M = 10.0%, SD = 13.0) Time 2: (M = 17.3%, SD = 21.9) and Time 3: (M = 14.9%, SD = 23.7); shakes: Time 1: (M = 6.9%, SD = 13.5) Time 2: (M = 7.3%, SD = 13.1) and Time 3: (M = 11.1%, SD = 18.3). Comparisons across time points and across complementary gesture functions revealed no significant differences. These questions often concerned whether the child wanted to participate in or end a certain activity (e.g., Nod + “Should we try the next one?”; Shake + “You don’t wanna play peek-a-boo?”). Others were aimed at clarifying the child’s intentions (e.g., Shake + “You don’t

4 Mothers’ nods sometimes accompanied messages permitting the child to perform an act (PA); these additionally accounted for a small average percentage of nodding gestures at Time 1 (1.5%) and Time 3 (1.8%). In effect, these head nods also provided indication of mothers’ approval of a certain behavior.

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like that?”; Nod + “You want me to draw it?”). Finally, questions were sometimes informational (e.g., Shake + “It’s not a power saw?”). In all cases, mothers at one and the same time posed a question through the verbal modality and provided a response in the nonverbal mode. In one sense, each of these gestures added information to mothers’ verbal messages and could be considered supplemental. However, questions can have an explicit affirmative or negative wording, such as when the mother clarifies the child’s desires (e.g., Nod + “You want me to draw it?”; Shake + “You don’t wanna play peek-a-boo?”). These gestures were scored as reinforcing the verbal message. The relationship between gesture and speech was more clearly supplemental when a yes/no question was worded neutrally (e.g., “Do you want to. . .”), as in cases that concerned topics beyond the ongoing activity. In total, across time points, 36.1% of head nods that accompanied yes/no questions were supplemental. For head shakes that accompanied yes/no questions, 6.5% were supplemental. 3.3.6. Gesturing while making statements At each time point, mothers used nodding and shaking gestures while making statements (nods: Time 1: (M = 16.2%, SD = 22.7), Time 2: (M = 13.0%, SD = 17.5) Time 3: (M = 13.2%, SD = 22.6); shakes: Time 1: (M = 26.7%, SD = 33.8) Time 2: (M = 35.1%, SD = 37.9) Time 3: (M = 32.2%, SD = 40.6). No differences across time points were detected for either gesture. Paired t-tests suggest that the average percent of head shakes used for statements was higher than for head nods at Time 2 (t(22) = 2.56, p = .034, d = .47) and marginally higher at Time 3 (t(20) = 1.99, p = .060, d = 43). In most cases, the head gestures reinforced the affirmative or negative content of these utterances, such as nodding with truth-functional statements like “That’s a kitty cat,” and “When you turn the crank [of the Jack-in-the-Box], it pops out,” but shaking the head while saying “It [toy car door] doesn’t open.” Head shakes sometimes mitigated an accompanying declarative statements; the addition of a head shake can reveal an otherwise implied negation (Kendon, 2002). For example, head shakes produced while saying “There’s only one left,” or “It’s just an orange ball,” could be described as reducing the force of otherwise affirmative sentences by negating a background presupposition (e.g., “There are no others left,” or “No, it’s not a proper orange”). Similarly, a small number of head nods mitigated accompanying utterances. For instance, in response to a child’s yes/no question about his drawing (“Is this like a star?”), the mother’s negative response, “Not really,” was tempered by an accompanying head nod. This sort of tempering aligns with the earlier reported finding that mothers often nod while correcting children’s utterances; rather than being critical, this mother gave a positive, gesture-based evaluation of the child’s drawing attempt, while giving a negative verbal evaluation. 4. Discussion This analysis revealed several intriguing patterns in the frequency and function of mothers’ head gestures while they played with their child, and in how the use of these gestures changed during the toddler years. Here, we review the key findings and then consider areas for future study. 4.1. Higher frequency of head nods compared to head shakes Mothers used more head nods than head shakes in their multi-modal messages to children. This pattern characterized the overall sample at each time point, and the individual behavior of most mothers. This finding parallels Guidetti’s (2005) report of French toddlers’ use of more head nods than head shakes with mothers at 16, 24, and 36 months of age. Given that the current observations occurred during play, the predominance of head nods over headshakes may not be surprising. This pattern may reflect the generally positive tone of parent–child play, or parents’ general optimism in their interpretation of their child’s behavior (e.g., Miller, 1995). A predominant function of mothers’ nods was to reinforce agreement with the child’s propositions, which were often labeling attempts. Rogoff (2003) describes these kinds of interactions as “language lessons.” Mothers in some cultures, including the U.S., encourage children’s early attempts to use verbal language by offering and eliciting labels, while responding with positive affect and sometimes mock excitement. Interestingly, even mothers’ corrections of children’s partially correct utterances were accompanied by a head nod, rather than a head shake conveying disagreement. Indeed, in most cases children only elicited explicit disagreement messages when they made a relatively egregious error, like calling an airplane a boat. It appears that these mothers aimed to encourage rather than criticize their young children’s language attempts. Future research might explore individual and cultural variation in this use of head gestures to support children’s language attempts. 4.2. Head gestures in dialog Most of mothers’ head gestures accompanied their verbal utterances, rather than serving as stand-alone yes/no messages. Aspects of mother–child dialog that incorporated head gestures included making and responding to declarative statements, as well as asking and responding to questions. Mothers’ head gestures were rarely used as responses to yes/no questions initiated by the child, though, by the third time point, head nods as affirmative responses became more common. In contrast, one of the most intriguing uses of head gestures across time points was to accompany the mother’s own simultaneous yes/no question. These gestures appeared to instantiate the response the mother presumed the child would offer to her question.

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By adding a head gesture, the mother creates a condition for the child to be a third-party recipient of both the question and answer in a yes/no question exchange. It is possible that these cases support the child’s participation in dialog, by giving the child opportunities to see question/response interchanges transpire, or, perhaps, by demonstrating how the child’s intentions can be translated into words and visible gestures. More research is needed on children’s comprehension of these gestures. While Fusaro and Harris (2013) demonstrated toddlers’ emerging understanding of head gestures used as isolated responses to yes/no questions, it is not yet clear whether head gestures facilitate the child’s grasp of accompanying verbal messages, such as in these simultaneous question–answer messages. 4.3. Using head gestures for behavior regulation In the course of dyadic interaction, both members of the dyad negotiate their mutual activities (Ninio & Snow, 1996), such as by continuing a certain activity or suggesting another. In this observational setting, caregivers often used head shakes to prohibit certain actions, particularly at the 14 month time point. These gestures may reflect the mother’s emotional response to the child’s behavior and her socialization goals. Observing the child carrying out an inappropriate behavior, like putting crayons into the mouth or drawing on a chair, seemed to trigger an action tendency (Fischer & Bidell, 2006; Frijda, 1986) aimed at stopping the behavior. By changing their voices, uttering prohibitions verbally, and shaking their heads, mothers communicated when the child’s behavior was not aligned with their expectations. The overall decrease in mothers’ head shaking frequencies from 14 to 30 months was largely driven by the relative absence of these messages at 30 months. This change may reflect, in part, fewer disruptive child behaviors involving the play materials at that time point. Another possibility is that, when the older children did engage in a prohibited behavior, they may have needed fewer prohibition messages, or less elaborated (i.e., multi-modal) messages, to regulate their behavior and shift their attention to something else. Messages that included head nods often signaled that a certain behavior was appropriate or presumably valued by the mother. Mothers’ head nods sometimes accompanied messages encouraging children to continue engaging in particular behaviors, or to initiate a particular play action. An open question is whether infants respond systematically to these signals by altering their current behavior and whether they adopt a more enduring positive or negative stance to a behavior or object in light of an adult’s non-verbal signals. For example, multimodal messages of encouragement to draw or to persist with a challenging toy might facilitate the eventual internalization of positive attitudes toward these activities and behaviors. Harris and Lane (2013) discuss evidence that gesture-based interactions can provide infants with a broad range of shortand long-term learning opportunities. Classic social referencing studies suggest that, by about twelve months of age, infants adjust their behavior toward an unfamiliar object or person in response to an adult’s affective facial and vocal cues (Campos, 1980; Mumme, Fernald, & Herrera, 1996; Sorce, Emde, Campos, & Klinnert, 1985). De Rosnay, Cooper, Tsigaras and Murray (2006) further found that infants from 12 to14 months were sensitive to mothers’ positive and negative appraisals of a stranger in the moment, and subsequently maintained their reaction to the new adult, even when the mother no longer provided affective signals. This suggests that the learning that occurs in social referencing interactions may be durable. Whether children incorporate parents’ evaluative head gestures into their own interpretation of a target, and the broader role of gesture in the service of parents’ socialization goals clearly warrant further study. 4.4. Social and cultural dimensions Head gestures can also be examined for their role in maintaining social interaction. In particular, back-channeling refers to the use of head nodding to demonstrate attentiveness to a communication partner (McClave, 2000; Yngve, 1970). This phenomenon is pervasive among listeners in adult-adult communication. Indeed, in the non-coded portions of the videotaped sessions, mothers often nodded in this way as they received instructions from the investigator. A form of back-channeling also appears to be at play in mothers’ responses to their children; in response to requests for acknowledgment, such as showing gestures and babbling, mothers often nodded and vocalized. This use of head nodding became more frequent over time, perhaps paralleling increases in children’s role as speaker in parent–child dialog. Among adults, cultural variation has been noted in the frequency and placement of head nodding and related short phrases (e.g., “uh-huh”) in conversation. In particular, Japanese adults produce head nods about three times more frequently than American English speaking adults as they converse (Maynard, as cited in Kita & Ide, 2007). These head nods, produced by both the speaker and listener, appear to establish positive feelings and social bonds among the conversation partners. These gestures are not solely elicited by the content of conversation, and instead seem to be used to establish coordination between conversation partners for its own sake. The mothers’ use of attentiveness gestures in the current study suggests that socialization in this use of gesture in conversational convention may begin as early as toddlerhood. Future studies should examine whether individual or cultural variation in parents’ use of these attentiveness gestures leads to differences in the developmental timing of children’s use of this non-verbal aspect of communication. 4.5. Individual differences in gesture frequency At each time point, we found no evidence of either a positive or negative correlation between the frequencies of mother’s use of the two head gestures. Thus, it does not appear that some mothers were simply more frequent users of gesture,

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systematically using more nods and more head shakes. Nor were mothers who more frequently used head shakes demonstrating a negativity bias by using fewer head nods. This finding may indicate that mothers’ use of head nodding and head shaking serve very different functions, even within one parent–child interaction, and are responses to different elicitors. Analysis of mothers’ gesture use over time revealed differences in inter-individual stability for the two gestures. We found more evidence of stability in head nodding frequencies over time, than in head shaking frequencies. This finding provides additional evidence for the interpretation that these two head gestures serve different functions in mother–child interactions during the child’s second year of life, and thus may draw on different sources for variation. For head shaking, which showed little evidence of inter-individual stability, the child’s behavior, which requires regulation by the mother, is the primary eliciting context of mother’s gestures. Such behavior is quite variable both within and across children in the second year of life. Further, children’s receptive language skills, and thus their abilities to understand verbal prohibitions, are extremely variable at this age, and mothers whose children have greater receptive language skills may not need to use as many head shakes to regulate behavior as those whose children have lower receptive language. Therefore, the lack of inter-individual stability in head shaking may be because head shaking is primarily elicited by the children’s behavior and is less reflective of a characteristic of the mother or the general qualities of her communication. On the other hand, we found a great deal of inter-individual stability in mothers’ frequency of head nodding. This finding suggests that the functions of head nodding in mother–child interactions are more reflective of a broader communication style. For example, the two most common pragmatic purposes of mothers’ head nods, making up more than 50% of all head nods across mothers, were to convey agreement with a speaker’s message and to show attentiveness. These are purposes that are relevant to dyadic interaction regardless of the age or roles of the speaker and listener. Head nods may be a strategy some mothers use to signal their attentiveness and responsiveness during interactions with their child.

4.6. Context-specific influences on gesture use As noted earlier, the specific context of this laboratory play session necessarily impacts the ways in which mothers use head gestures. In some cases, the setting poses limits on mothers’ gesture use. For example, other unique uses of head gestures may be evident in settings with multiple children, or during non-play interactions. On the other hand, the availability of picture books and the novelty of the testing room provided opportunities for parents and children to produce and respond to verbal labels; gesture use may vary as a function of the availability of such interesting things to talk about. Another relevant contextual feature is the extent to which the setting offers a physically safe space for the child to navigate. In this particular setting, children had a rather limited space in which to move about, and mothers were often concerned about the child’s meddling with other materials in the room. These features likely impacted the relative frequency of prohibition messages. Other novel settings, such as doctors’ offices, and cultural institutions like libraries and churches might also elicit similar responses. Nonetheless, in the current laboratory setting, mothers were relatively free from distractions, which may have helped them keep the child engaged in the mutual activities and away from the extraneous features of the setting. Future studies should consider these types of environmental constraints on parent–child communication.

5. Conclusion This study provides insight into the use of two conventional head gestures in mothers’ communication with their young children. Mothers used head nodding and head shaking gestures to convey a wide variety of communicative messages. The distribution of these messages shifted across the three time points, reflecting changes in the child’s motor and language behavior that elicited different types of responses from mothers. Marked individual differences at each time point were detected in caregivers’ gesture production, warranting further study. In particular, the stability of head nods over time suggests that this aspect of parent behavior may be part of a broader difference in communication style. These patterns in gesture use raise new questions about the extent to which differential use of head nods and head shakes impacts children’s involvement in communication and their behavioral regulation. Head gestures in adult–child communication provide insights into infants’ developing social and communication skills that extend beyond what we can learn from exchanges involving pointing. Caregivers’ head gestures likely facilitate children’s language learning in at least two ways: by providing feedback and encouragement in the early uses of vocabulary, and by providing practice in question–answer discourse patterns through mothers’ combined production of yes/no questions and answers. Further, the use of head gestures for behavior regulation essentially creates natural social referencing encounters that could impact social learning. Caregivers’ head gestures might help children bridge from their understanding of the social interaction context to an understanding not only of (a) the verbal utterances they accompany, but also (b) how the tools and objects in their culture can and should be used, (c) norms about appropriate behavior more broadly, and (d) various communicative exchanges that involve head gestures, such as the format for asking and answering questions, and for expressing agreement and disagreement. Future studies of children’s comprehension of head gestures are needed to understand whether and when these gestures facilitate the child’s comprehension of caregivers’ verbal messages and the child’s internalization of the values expressed through those messages, even when early language production skills are just emerging.

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