Characterizing the Richness of Maternal Input for Word Learning in Neurogenetic Disorders

Abstract

Promoting language abilities, including early word learning, in children with neurogenetic disorders with associated language disorders, such as Down syndrome (DS) and fragile X syndrome (FXS), is a main concern for caregivers and clinicians. For typically developing children, the quality and quantity of maternal language input and maternal gesture use contributes to child word learning, and a similar relation is likely present in DS and FXS. However, few studies have examined the combined effect of maternal language input and maternal gesture use on child word learning. We present a multidimensional approach for coding word-referent transparency in naturally occurring input to children with neurogenetic disorders. We conceptualize high-quality input from a multidimensional perspective, considering features from linguistic, interactive, and conceptual dimensions simultaneously. Using case examples, we highlight how infrequent the moments of word-referent transparency are for three toddlers with DS during play with their mothers. We discuss the implications of this multidimensional framework for children with DS and FXS, including the clinical application of our approach to promote early word learning for these children.

Keywords

Down syndrome - fragile X syndrome - maternal language input - maternal gesture use - word learning

Learning Outcomes: After reading this article, the learner will be able to (1) summarize early communication development in Down syndrome and fragile X syndrome; (2) explain the transactional model within the context of language learning; (3) summarize the linguistic, interactive, and conceptual dimensions of word-referent transparency; and (4) apply the multidimensional framework to identify word-referent transparency.

Individuals with neurogenetic disorders, such as Down syndrome (DS) and fragile X syndrome (FXS), characteristically struggle with spoken language throughout the life course.[1] [2] Promoting language abilities in these populations is a main concern for caregivers and clinicians, leading researchers to be as invested in this issue, because increased language ability is associated with greater independence and community inclusion.[3] [4] [5] However, our understanding of the mechanistic factors that underlie early word learning and use in these populations is limited. We propose that responsive and lexically rich language input coupled with maternal gesture use are key factors for promoting word learning and use in children with DS and FXS.

It is well-established that the quality and quantity of maternal language input and maternal gesture use contributes to children's vocabulary growth in typically developing children.[6] [7] [8] Given this, it is likely that a similar relation is present in children with DS and FXS, but there is limited research in this area, especially in toddlerhood. Furthermore, much of the research on maternal language input and gesture use have focused on these behaviors separately as predictors of child language abilities, but few studies have examined their combined effect. In this article, we introduce an approach for characterizing the richness of maternal input for word learning in DS and FXS from a multidimensional perspective. First, we provide an overview of early communication development in DS and FXS. Next, we introduce the transactional model as the theoretical framework guiding this work and our application of Rowe and Snow's[9] framework to characterize variation in word-referent transparency in maternal input. With this information, we then present and apply our approach to three mothers of toddlers with DS to reveal differences in mothers' use of nouns that are responsive to the toddlers' engagement states and are supported with maternal gesture during free play. We conclude with a discussion of our approach and its application for intervention in DS and FXS.

Early Language in Down Syndrome and Fragile X Syndrome

Both DS and FXS are associated with intellectual disability, presenting with mild to severe cognitive impairments emerging in infancy.[10] [11] [12] [13] Early delays in spoken vocabulary set the course for later language disorders.[2] The development of prelinguistic skills—the use of eye-gaze, vocalizations, and gestures to communicate—precede the acquisition of first words and support language learning.[14] For infants with DS and FXS, prelinguistic skills are also delayed.[15] In DS, a mixed profile of strengths and difficulties emerges in infancy, indicating impairments in early vocalizations coupled with strengths in gesture use.[16] [17] Although less research has explored prelinguistic skills in FXS, these studies consistently demonstrate early gesture impairments.[18] [19] [20]

Given the established risk for language disorders associated with DS and FXS, children with these conditions usually begin to receive early intervention services within the first year of life as both of these neurogenetic disorders can be diagnosed pre-, per-, or postnatally.[21] [22] However, it is important to note that while FXS can be diagnosed pre-, per-, or postnatally, diagnostic testing is not commonly performed at these times. In fact, the average age of diagnosis for FXS occurs between 35 and 37 months for males and at 41 months for females.[23] Nonetheless, there is strong evidence establishing the need for early language intervention for children with DS and FXS.

Although typically developing infants usually acquire first words between 10 and 15 months,[24] toddlers with DS and FXS say their first words later. The average age of first words for toddlers with DS is 18 months (range: 9–24 months).[25] In contrast, toddlers with FXS say their first words around 26 months of age[26] [27] and the range for age of onset is very large (10–45 months).[26] [28] Less is known about the rate of growth for spoken vocabulary for children with DS and FXS, but from the available studies, spoken vocabulary growth appears to be significantly slower in DS and FXS than it is in typically developing children. For example, while the spoken vocabularies of typically developing children increase to 50 words around 18 months, only 73% of children with DS have spoken vocabularies of 50 words or more by 5 years of age.[17] [29] [30] In other words, there are children with DS who still have not yet acquired a spoken vocabulary of 50 words at the age of 5 years. Given what is known about protracted vocabulary development in DS and FXS, there is a clear need to identify targets and supports for early vocabulary interventions.

Transactional Model

Our approach to understanding the maternal contributions to early vocabulary development in DS and FXS is grounded in the transactional model and its application to caregiver–child interactions. The transactional model proposes that development is the result of bidirectional, reciprocal interactions, or transactions, between the individual and their environment.[31] [32] These interactions are often referred to as a dance between the child and the caregiver, with each partner influencing the participation and responsiveness of the other.[33] When applied to language development, children learn language through social interactions with a caregiver in their environment,[34] [35] [36] which often is a result of the responsiveness of their caregiver to child communication.[37] [38] Importantly, child engagement during these interactions also impacts child language outcomes, such that children who are more actively and reciprocally engaged with their caregiver around an object of interest have better language outcomes.[39] [40] [41] [42]

Influence of Child Communication Acts

Prior to spoken words, children use prelinguistic communication—eye gaze, vocalizations, and gestures—to communicate.[43] Unfortunately, children's prelinguistic communications can be easily missed. That is, eye gaze requires that the caregiver is actively attending to the child and can see the nuanced movement of their eyes in time to respond. Vocalizations can provide caregivers with more cues to communicative intent, but at times these vocalizations may seem undirected, making it difficult for the caregiver to understand the child's intent. When young children add gestures to early vocalizations, their communicative intent becomes clearer to their caregivers because gestures direct the partner's attention to the object or event of interest. This allows caregivers to provide more precise input for children to map words in the input to referents in the world,[44] [45] [46] [47] leading to a bidirectional interaction and more effective caregiver–child communication during the prelinguistic period.

Caregivers often interpret potentially communicative behaviors, including canonical babbles, gestures, and gesture + vocalizations by responding with the language the child would say if they were able. For example, if a child points at a ball, their mother can respond with the label “ball,” connecting the word to the object they are interested in.[48] This example also highlights that the type of gesture the child uses may influence the mothers' language input.[49] Proto-declarative (commenting) gestures—most often points—are more likely to result in maternal utterances that include object labels (nouns). In contrast, proto-imperative gestures—most often reaches—may be more likely to elicit maternal utterances made up of action or mental state words (verbs) related to giving the child the wanted item or the assistance needed. Importantly, proto-declarative gestures are stronger predictors of word learning than proto-imperative gestures.[49] [50] [51] When caregivers combine a gesture with their responsive input, children are also more likely to respond with speech.[52] [53] Once children begin to use spoken words, another bidirectional interaction emerges. As children learn words from their caregiver and their vocabularies increase, caregivers adjust their language input to meet the child's increasing abilities.[7]

Maternal Responsivity

Maternal responsivity refers to a healthy, growth-producing mother–child relationship characterized by warmth, nurturance, and stability, and it is a well-established predictor of language development, including word learning.[54] [55] [56] Mothers demonstrate responsivity through their use of language and gestures when responding to their child's signals during an interaction (see [Table 1] for definitions and examples).[57] [58] For example, if a child's attention is focused on a puzzle, this is a signal of the child's interest that can lead their mother to be responsive. Specifically, the mother can respond to this interest by labeling the piece the child is manipulating, “it's a barn,” while pointing to the corresponding picture where the piece goes on the puzzle. Together, maternal language input, including the precise properties of linguistic input, and gestures provide maximally supportive input for word learning.

Table 1 Definitions and Examples of Common Input and Gestures for Maternal Responsivity

Maternal responsivity	Definition	Example
Input variable
Follow-in commenting	Talking about the child's focus of attention without telling the child what to do or directing their behavior	Child is looking at a book about farm animals and points to a pig Mother responds, “That's a pig”
Follow-in directing (redirects)	Talking about the child's focus of attention while suggesting the child change some aspect of their play with the toys, or redirecting the child	Child is doing a puzzle Mother says, “Can you put it in?”
Linguistic mapping	Translating a child's nonverbal communication into words	Child is reaching for their cup Mother says, “You want your cup?”
Repeating	Repeating the child's immediately preceding approximation of a word with adult pronunciation	Child approximates, “All Done” Mother says, “You're all done?”
Expansion	Adding words or grammatical structure to the child's immediately preceding spoken utterance	Child says, “Dog in” Mother says, “The dog goes in the box”
Gesture variable
Deictic	Expressing communicative intent—sharing attention, commenting, requesting
Point	Extension of the index finder toward a proximal or distal person, object, location, or event for the purposes of sharing attention or requesting	Child points to their cup
Show	Holding an object toward a communication partner's line of sight while making eye contact or orienting their body to the communication partner	Child finds a rock and holds it up to their mother to show it to her
Give	Extension of the arm while holding an object toward the hand of a communication partner with the intent of them taking the object	Extending arm holding a cup toward their mother to request more water
Representational	Referring to a referent with or without the physical object	Drink = bring toy cup to mouth Phone = put palm of hand to ear
Conventional	Form and meaning are culturally defined	Nodding head “yes”

Maternal Language Input

Investigations of maternal responsive language input have focused on follow-in comments, follow-in directives, repeating, linguistic mapping, and expansions (see [Table 1] for definitions).[59] [60] [61] [62] In these studies, mothers' verbal responsiveness is coded only after determining the child's active engagement (i.e., the child's signal). These studies suggest that verbal responsiveness supports spoken vocabulary development in typically developing infants, and there is emerging evidence for the same relationship in children with autism spectrum disorder. Furthermore, follow-in labeling (e.g., That's a cow {Mom points}) or commenting (e.g., You want your cup {Mom shows}) with a deictic gesture may be particularly supportive because these utterances follow the child's attentional focus and the maternal gesture simplifies the word learning process.[49] [59] [63] [64]

As children are learning their first words, the amount of speech children are exposed to has been linked to differences in toddlers' vocabulary growth.[6] [7] [65] Measures used in studies of linguistic input tend to be based on the number of total words. However, these measures may be too general to characterize the kind of linguistic input children with neurogenetic disorders need to support initial vocabulary development. For example, Trueswell and colleagues[66] recently demonstrated that the extralinguistic information known to support the mapping between words and their referents, such as child attention to the concrete object or parent gesture, were infrequent in naturally occurring play interactions. In a study using adults to simulate infant word learners, only 18% of video segments contained sufficient information for adults to accurately guess the common noun the parent had uttered when a beep replaced the noun in a silent video of parent–toddler interaction. In other words, most exposure to nouns in caregiver input is too ambiguous to support early word learning. This suggests that characterizations of high-quality language input should document the more infrequent, but potentially more powerful moments, of word-referent transparency where maternal noun input is coupled with child engagement, maternal responsivity, and gesture use.

Maternal Gesture

Maternal gesture use is positively associated with early language development in typically developing toddlers.[8] [52] Common gesture forms include deictic (point, show, give), representational, and conventional gestures (see [Table 1] for definitions and examples). In early development, gesture use by mothers is simple, concrete, usually reinforced with speech, and context-based.[52] [67] By using gestures during interactions with their child, mothers are providing a scaffold for communication and word learning.[36] As mentioned earlier, when a maternal gesture is combined with responsive language input (e.g., That's a cow {Mom points}), the gesture provides additional nonverbal support for word learning by establishing a clear connection between the word and its referent.[8] [45] [46] [68] [69] We suspect that the combination of these highly supportive features in the interactive and conceptual dimension are especially important for children with neurogenetic disorders.

Characterizing Word-Referent Transparency

Based on the available research, it is clear that responsive and lexically rich language input coupled with maternal gesture use are key factors for promoting word learning. However, most studies of maternal input quality have focused on maternal responsivity to children's communication acts and attempts[9] [70] with an emphasis on the communicative function of maternal utterances (e.g., labeling, commenting, requesting). To date, little attention has been given to how words are used and how maternal gestures support the learning of early words. The coding scheme presented in this article is designed to identify features of high-quality input that are hypothesized to support the learning of first words for toddlers with neurogenetic disorders. In the next section, we describe this coding scheme and its implementation with mother–toddler dyads, including three case studies of toddlers with DS. Following Rowe and Snow,[9] we conceptualized high-quality input from a multidimensional perspective, considering features from linguistic, interactive, and conceptual dimensions simultaneously ([Fig. 1]).

Figure 1 Framework for richness of maternal input for word learning.

In the linguistic dimension, we focus on nouns in maternal input because children's first words are primarily names for things. In the interactive dimension, we are primarily interested in maternal responsivity to children's engagement states and communicative behaviors because the use of follow-in labeling and comments has been identified as an input property that promotes early word learning. In the conceptual dimension, we are interested in maternal use of deictic gestures—point, show, give—when coupled with maternal noun use. The addition of a maternal deictic gesture is expected to increase word-referent transparency by making the connection between the noun in the input and the referent in the world more explicit. Taken together, we propose that support for word learning is optimal when maternal input and gesture work together to create maximal word-referent transparency[66] in the context of bidirectional, reciprocal interactions between the child and the mother. Thus, when a mother notices and responds to her child's communication bid and provides them with noun input coupled with a deictic gesture, she has provided the child with high-quality input across all three dimensions.

A Multidimensional Coding Scheme for Word-Referent Transparency

This coding scheme was designed to be used with mother–toddler dyads during a video-recorded free play interaction. The videos of play sessions are then transcribed and maternal language is coded using Systematic Analysis of Language Transcripts (SALT) software.[71] Child engagement states as well as child and maternal gesture are coded from the video recordings using the The Observer XT 14 (Noldus) software.[72] Elapsed time in 30-second increments are noted in the SALT transcripts so that maternal utterances can be aligned with the second-by-second time increments in the Noldus for the behavioral coding ([Table 2]).

Table 2 Multidimensional Coding Scheme for Word-referent Transparency Definitions and Examples

	Definition	Example
Linguistic codes
Referentially transparent noun [N]	A common noun can be identified by a preceding article a/the or plural inflection; it is referentially transparent if it refers to a picture or concrete object in the play environment	Cow [N], spoon/s [N]
Label [L]	Single nouns, noun phrases, or sentences with the linguistic form pronoun + copula + noun phrase	A cow [N], yellow duck [N] That/'s the duck [N] [L]; they/'re spoon/s [N] [L]
Comment [C:S], [C:O]	Simple sentences with declarative word order. Either the noun is the sentence subject, or it is the object of the verb or preposition	Chicken [N] go/s right there [C:S] You have a bracelet [N] [C:O] You put them in the truck [N] [C:O]
Engagement state codes
Object	Child is actively engaged with an object and manipulates it. This can include holding the object and looking at it. Caregiver and child are not interacting with each other	Child focused in building a tower with blocks
Supported joint	Child and caregiver are engaged with the same object, but the child is not actively including the caregiver in the interaction. The caregiver supports the interaction by helping the child shift the focus of attention. The child might look at the caregiver occasionally and briefly but does not display sustained interest in the caregiver. The caregiver can support the interaction by asking, requesting, or gesturing	Child and mother are playing with blocks and she encourages the child's play by saying, “Can you stack them?” The child places one block on another but does not look at or respond to the mother
Coordinated joint	Child and caregiver are engaged with the same object and the child actively and repeatedly acknowledges and includes the caregiver as a participant of the interaction. Child might acknowledge the caregiver as a participant by making repeated eye contact with the caregiver, pointing, gesturing, or conversing with the caregiver	Child and mother are building a tower with blocks together, the child puts on a block, looks at the mother and back to the tower, claps and vocalizes while smiling. The mother puts on another block, the child looks at her then to the tower, and back to her then vocalizes and claps again
Gesture codes
Deictic	Expressing communicative intent—sharing attention, commenting, requesting (point, give, show)	Point—pointing to a dog Show—holding up a ball Give—extending arm holding a wind-up toy toward their mother to request activating it
Representational	Referring to a referent with or without the physical object	Drink—bring toy cup to mouth Phone—put palm of hand to ear
Conventional	Form and meaning are culturally defined	Shaking head “no”
Ritualized requesting (child only)	Requesting a wanted item	Reaching or reaching with an open-close hand motion to a wanted toy
Sign language	Use of American Sign Language or baby sign	Signs, “All done”
Follow-ins
Follow-in commenting	Talking about the child's focus of attention without telling the child what to do or directing their behavior	Child puts blocks in a toy truck bed Mother says, “you put them in the truck?”
Follow-in labeling	Providing the label for the object that is the focus of the child's attention	Child is holding a puzzle piece Mother says, “that's a barn?”

Linguistic Coding

Maternal utterances are coded using SALT for maternal linguistic input (see [Table 2] for definitions and examples). A word-level code [N] is added to all referentially transparent nouns in maternal utterances. Referentially transparent nouns refer to pictures or concrete objects in the play environment. Nouns with abstract referents are not coded (e.g., a good throw; high five, the rest, a minute, noise), nor are addressee terms (e.g., buddy, friend, child's name), or the mother's use of mom to refer to herself. Utterance-level codes are added to maternal utterances with nouns in simple sentences that (1) labeled an object or (2) commented on an object. Labels are coded [L] and include single nouns or noun phrases (e.g., cow, blue pants) or simple sentences with the linguistic form pronoun + copula + noun phrase (e.g., that's the duck; they're spoons).[73] Simple sentences with declarative word order are coded as comments. The utterance code [C:S] is added when a noun appeared as the sentence subject and [C:O] is added when a noun appeared as the object of the verb or preposition. Maternal utterances meeting the syntactic criteria for labels and comments are coded, regardless of rising intonation (e.g., that's a barn? you put them in the truck?) or a tag question (e.g., you love those books, don't you?). However, label and comment codes are not added to complex sentences because these sentences are assumed to be too advanced for the toddlers' developmental level. This linguistic coding scheme allows us to determine total noun use as well as noun use during follow-in labeling and commenting with and without a deictic gesture when aligned with the behavioral coding.

Engagement State and Gesture Coding

Each behavior—child engagement state, child gesture, maternal gesture—is coded within one observation file in separate passes to ensure that no behaviors are missed, while allowing all behaviors to be viewed together (see [Table 2] for definitions and examples). Child engagement is coded using the procedures and coding scheme of Hahn and colleagues[74] based on the work of Adamson and colleagues.[75] [76] In this coding scheme, codes are based on the engagement of the child during a naturalistic interaction (free play). Object engagement occurs when the child is actively engaged with an object and manipulates it, but their mother is not actively involved in their object exploration. This can include holding the object and looking at it. Supported joint engagement occurs when the child and mother are engaged with the same object with the interaction being supported by the mother as she scaffolds their focus of attention. The child might look at the mother occasionally and briefly but does not display sustained interest in the caregiver. In coordinated joint engagement, the child and mother are actively focused and engaged with the same object. This is a dynamic interaction where the child is actively and repeatedly acknowledging and including their mother as an active participant in the interaction. The interaction is characterized by the child repeatedly making eye contact with their mother, as well as pointing, gesturing, or conversing (babbling, vocalizing) with her.

The coding scheme for both child and maternal gesture was developed based on the work of Iverson and colleagues.[52] [77] [78] [79] Specifically, we code deictic (point, show, give), representational, and conventional gestures for both children and mothers. We also include a code for ritualized requesting gestures for children only (not mothers) and a code for sign language for both mothers and children due to its frequent use as an alternative form of communication for young children, especially those with DS. For children, gestures are coded when they have a communicative function (commenting, requesting). For mothers, gestures are coded when they are part of a communication act that is directed toward the child. Gestures are coded as distinct point estimates, such that the hand/arm movement needs to fully change motion for a new gesture to be coded. For example, if a mother repeatedly performs a touch point to the same image in a book (sometimes referred to as a tapping point) this would be coded as one point.

Follow-in Coding for Labels and Comments

Once the linguistic, engagement state, and gesture coding are completed, they are aligned to identify moments of maximal word-referent transparency. Any maternal utterance that contains a noun is located in the video by matching the timing information in the SALT transcripts with the Noldus time codes to determine if the maternal utterance occurs when the child's attention is peaked and can be an opportunity for a follow-in label or comment (see [Table 2] for definitions and examples).[40] [59] [60] If the child is in a state of engagement with an object (i.e., child object engagement, supported joint engagement, or coordinated joint engagement), the coder watches the video to determine if maternal utterances coded as labels or comments in the SALT transcript are about the object the child is engaged with. Reviewing the video is important because the mother and child can be focused on different parts of a toy such as a puzzle with multiple pieces. For example, the child could be trying to put in a certain piece while the mother was labeling a different piece. If the child is engaged with the object and the mother's utterance is a label or comment about that object, it is coded as a follow-in label or comment with or without a maternal gesture. If the follow-in utterance is combined with a maternal gesture, it is coded as deictic, other (i.e., conventional or representational), or sign. The last step is to copy the utterance from the transcript into the comment line in the Noldus. This allows us to have a complete behavioral and linguistic characterization of the whole moment.

Case Examples of Toddlers with Down Syndrome

To explore the utility of our multidimensional coding scheme for word-referent transparency, we present case examples for three mothers of toddlers with DS. Mother–child interactions in DS have been examined with some frequency given the social strengths of children with DS,[80] including explorations of early communication development. Research suggests that mothers recode the gestures used by children with DS, providing linguistic input related to their children's nonverbal communication.[81] For example, the child points to a picture of a dog and their mother responds, “That's a dog.” Interestingly, mothers of children with DS and with typical development recode a similar amount of gestures.[69] [81] However, there is a developmental shift with mothers of typically developing children reducing their use of gesture recodes as children age, whereas mothers of children with DS continue to recode child gestures as they age.[81] Therefore, mothers of children with DS may be more likely to interpret potentially communicative behaviors and respond to the child with the words for their communication than mothers of typically developing age-matched[82] and expressive language-matched peers.[77] If there is a tendency of mothers to respond to potentially communicative behaviors, this provides an avenue for early interventions that teach parents to be responsive to their child's communicative acts and, in turn, improve their language outcomes.[83] [84]

There is limited research on maternal language input in DS, especially in children younger than 2 years when they begin to say their first words. Like mothers of typically developing children, mothers of children with DS tailor their language input to match their child's communicative abilities. However, they continue to use simpler language input later in development than typically developing mothers. Generally, they use fewer words, shorter or fewer utterances, and fewer conversational turns than mothers of age-matched typically developing children.[64] [82] [85] Iverson and colleagues[77] also noted that mothers of children with DS used fewer utterances overall than mothers of typically developing children with similar language abilities and that the number of maternal utterances decreased as the lag between chronological and expressive language ages increased. These studies provide important broad descriptions of the linguistic properties of maternal input to children with DS, but do not reveal whether mothers of children with DS enrich the quality of their input to support initial word learning. This remains a crucial question, given that, compared with typically developing children, children with neurogenetic disorders have more limited abilities to use the social and attentional cues for word learning.

The addition of maternal gesture to language input may further support word learning for children with DS. For example, mothers of children with DS are more likely to produce a simple response containing a single utterance supported by a single gesture, compared with mothers of typically developing children.[77] This provides clear one-to-one correspondence. Also, mothers of children with DS tend to use more gestures combined with an utterance when the gap is larger between children's chronological and expressive language ages (i.e., more gestures used when children were older with lower expressive language ages). Thus, it seems mothers of children with DS are sensitive to the fact that children with large gaps require gestures to support comprehension. Nonetheless, there is a need to characterize input quality across linguistic, interactive, and conceptual dimensions to better understand how mothers support word learning for their children with DS and how supportive properties can be enhanced.

Participants and Procedure

Participants were three toddlers with DS (two males, one female) between 24 and 30 months and their mothers (30–39 years of age). As part of a larger battery, mothers were instructed to play with their children as they normally would for least 15 minutes of free play with a standard set of toys. Mothers completed the MacArthur-Bates Communicative Development Inventory—Words and Gestures (CDI),[86] a caregiver-report tool that assesses day-to-day communication and language skills, including 396 early words understood and spoken and 63 common gestures. The coding scheme described earlier was used to code the mother–child free play for maternal linguistic input, child engagement, gesture use, and follow-ins. In addition, maternal utterances were coded following standard SALT conventions and the procedures of Hadley and colleagues[87] to compute three general input measures for descriptive purposes: (1) number of utterances, (2) number of different words (NDW), and (3) mean length of utterance (MLU). See [Table 3] for summaries of the children's performance on the CDI.

Table 3 Input Properties for Three Toddlers with Down Syndrome and their Mothers

	P1	P2	P3
Child
Age in months	24	29	30
CDI words understood[a]	92	301	129
CDI words produced[a]	14	14	39
CDI early gesture[a]	17	15	0
CDI later gesture[a]	19	34	11
Mother
Total utterances	303	206	220
Total words	1187	576	669
Words per min	81.8	40.13	48.53
MLU in morphemes	4.24	2.91	3.22
Number of different words	199	134	138
Total nouns	153	70	50
% of total words	0.13	0.12	0.07
Nouns in follow-in
Label	40	28	10
Comment: subject	3	1	2
Comment: object	12	6	0
All follow-in	55	35	12
% of total nouns	0.36	0.50	0.24
Follow in with deictic gesture	16	13	3
% of total nouns	0.10	0.18	0.06
With any gesture[b]	19	13	4
With a sign	0	0	3
Child initiated word-referent transparency[c]	5	6	0

^a CDI (MacArthur-Bates Communicative Development Inventory-Words and Gestures) uses a raw score count for words understood, words produced, early gesture, and later gesture.

^b Maternal deictic, conventional, and representational gestures.

^c Moments where a child's use of a deictic gesture proceeds a mother's follow-in utterance.

Results

[Table 3] summarizes the linguistic properties of the mothers' input, including general input measures such as total utterances, MLU, and NDW. Noun use with different degrees of interactive and conceptual support is also described. Comparison of the general input measures across mothers revealed that two mothers were similar on general input measures (P2, P3). Both produced approximately 200 complete and intelligible verbal utterances in 15 minutes, used an average utterance length of approximately 3 morphemes, and exposed their children to 130 to 140 different words. Interestingly, their two toddlers were close in age at 29 and 30 months, respectively. In contrast, the mother of the youngest toddler (P1, 24 months) produced 303 complete and intelligible verbal utterances and used longer utterances and many more different words. Analysis of maternal use of nouns revealed one primary similarity. Nouns made up only 7 to 13% of the words addressed to the three children. Despite playing with the same set of toys, only eight nouns (i.e., bag, book, bear, cat, cow, duck, house, and puzzle) were used by all three mothers, and only 11 nouns were used collectively more than 10 times (i.e., animal, baby, bag, book, duck, goat, hat, kitty, pig, puzzle, and truck). Thus, in most cases, children were exposed to names for objects with minimal input frequency.

Moving to the use of nouns during follow-in labels and comments, all three mothers had a higher frequency of noun use during follow-in labeling than during follow-in commenting ([Table 3]). Recall that follow-in labeling and commenting were coded only when the mother's utterance aligned with the child's focus of attention. Follow-in utterances with nouns accounted for less than 20% of mothers' total utterances, but when nouns were used, they followed in to the child's attention 24% to 50% of the time. The addition of a maternal gesture to a follow-in utterance with a noun created optimal word-referent transparency. Mothers used a gesture in 33% to 42% of their follow-in labels or comments. However, less than 20% of mothers' total nouns had this maximum degree of support. Finally, to examine the full bidirectional interaction, we also identified which follow-in utterances were initiated with a child deictic gesture. Only the two children (P1, P2) who had more advanced gestural repertoires according to the CDI experienced these rich child-initiated learning moments.

This analysis demonstrated that although children showed moments of focused attention to objects during play and mothers were responding with clear gestural and linguistic input that provided children with high-quality input for word learning, rich moments were relatively rare. It is also important to note that not all nouns coded as labels or comments in the transcripts were coded as a follow-in when juxtaposed with the video data. Specifically, they were not coded as follow-in when the child was engaged with an object and the mother labeled another object that was not in their child's direct line of sight. For example, one child, located to the left of their mother, was intently exploring a cat figurine, when the mother picked up a dog figurine to her right saying, “it's a dog,” but the mother did not bring the dog to the child's attention. This example demonstrates that not all words in parent input provide high-quality word learning opportunities. In this example, the mother could have created a richer and more supportive moment by pointing to the cat that had captured her child's attention and saying, “you have a cat,” providing clear and optimal word-referent transparency.

[Table 3] also includes instances of multimodal input, when parents both said and signed a word. It is common for parents and clinicians to use sign language with infants and toddlers with neurogenetic disorders, especially those with DS. Sign language represents a form of unaided alternative and augmentative communication, which involves mapping the sign to the referent. However, if the child has not yet learned that the sign represents the referent or object in the play environment, the connection between the object, sign, and word will still be unclear. As such, we have included the use of follow-in labels and comments with a sign in [Table 2] for informational purposes, but do not view these as gestures that maximize word-referent transparency.

Implications for Maximizing Input Quality for Children with Neurogenetic Disorders

To date, no studies have focused on noun input to children with DS or FXS as they are learning to say their first 50 words. Although providing linguistically rich and supported word learning opportunities is important for all children, this need is even greater for those with neurogenetic disorders with established risk for language disorders. Children typically learn nouns for common objects during social interactions with their caregivers. Learning words in this context requires robust use of social and attentional cues because unambiguous moments of word-referent transparency are rare during naturally occurring interactions.[66] Use of these cues is likely to be more difficult for children with neurogenetic disorders because many have difficulties with attention shifting abilities. For these children, we need to enrich the linguistic properties of input as well as the supportive interactive and conceptual properties of input. Thus, to help caregivers support their children's early word learning, we need to help them enrich their input along all three dimensions. This will result in caregivers talking differently, not talking more. Specifically, we recommend coaching caregivers to follow in to their child's engagement state, to notice the object the child is attending to and give the object its name, and to combine the name with a deictic gesture. Caregivers may also need to be coached to increase wait time between their utterances to give children time to comprehend the words in their input and to open up space for their children to initiate.

Application of our coding scheme through the case study revealed differences in the quantity and quality of noun input to toddlers with DS from a multidimensional perspective. Specifically, we observed differences in the number of instances of maternal noun use characterized by word-referent transparency, supported by maternal or child gesture. High degrees of word-referent transparency may be particularly important for facilitating spoken vocabulary growth for children with neurogenetic disorders. However, we suspect that differences in behavioral phenotypes associated with each neurogenetic disorder[88] may result in different profiles of maternal input quality across populations.

For populations with gesture strengths, such as DS,[17] [81] [89] more instances of word-referent transparency may be driven by the child as illustrated by two of our three case examples. For children with weakness in gesture, such as those with FXS,[18] [19] [20] [90] it may be even more difficult for mothers of children with FXS to provide follow-in comments because their children are not using gestures frequently. Although other potentially communicative behaviors, like vocalizations or eye-gaze, can be used by children to indicate their interest, vocalizations may occur infrequently, and eye gaze is more difficult to notice. Thus, the available research on FXS suggests that opportunities for linguistically rich and supported maternal input may occur with even less frequency.

Implications for Clinicians

Although we acknowledge that it is not feasible for clinicians to code their behavioral samples using our coding scheme, clinicians can begin to view their samples through a multidimensional lens to determine whether caregivers are providing interactive and conceptual support for early word learning for children with DS and FXS. Specifically, clinicians can help caregivers begin to notice when their child is socially engaged with attention on an object and provide a follow-in label or comment. They can also help caregivers learn to create comment-worthy moments by making objects appear, move, and change. Clinicians can also coach caregivers on the linguistic properties of their utterances. In this early period of word learning, isolated nouns or nouns in the final position of a labeling sentence (e.g., that's a pig; here's a cow) or comment (e.g., you found a pig) may be most salient.[64] Clinicians can also coach caregivers to couple the follow-in label or comment with a deictic gesture to increase the conceptual support for word-referent transparency.

There is a clear need for evidence-based naturalistic language interventions that are designed to provide children with DS and FXS with more support for early vocabulary learning.[15] [84] [91] [92] [93] [94] [95] Language intervention studies in DS have indicated that high levels of maternal responsivity lead to child language growth[95] and that mothers can be taught to be responsive.[83] [96] [97] [98] However, it has also been suggested that children with DS need to be taught words more directly.[98] Therefore, our multidimensional approach is well positioned to support and expand our understanding of the efficacy of parent-implemented vocabulary interventions for toddlers with DS.

Maternal responsivity has been established as a predictor of language development (receptive language, expressive language, rate of different words) in early childhood[92] and over the course of childhood[93] and adolescence[94] in FXS. In the only intervention study in mother–child dyads with young children with FXS, McDuffie and colleagues[91] used a single-subject design to enhance maternal verbal responsiveness. They found that mothers increased their use of follow-in commenting over the course of the intervention; however, intervention effects were not observed for maternal contingent responding to child communication acts. Although these findings suggest that mothers of children with FXS can learn to use follow-in commenting, the findings should be interpreted with caution given the study's small sample size (n = 6). It is also important to note that maternal responsivity relies on the behaviors of the child. That is, children with FXS who have higher rates of communication tend to have more responsive mothers, due in part to these mothers having more opportunities to respond contingently to child communication acts.[91] [99] In addition, maternal gesture use is related to language abilities in children with FXS, similar to other populations.[53] Furthermore, the combination of a maternal utterance with a gesture is more likely to lead to a verbal response from a child with FXS, suggesting that maternal input with a gesture is a powerful tool for language development. Taken together, the stage is set to examine how maternal language input and gestures support word learning in FXS.

Conclusion

In this article, we have presented a multidimensional approach for examining word-referent transparency in naturally occurring input to children with neurogenetic disorders. Based on the current evidence, it is clear there is a need to characterize the complex, bidirectional interactions in which word learning occurs. Unfortunately, existing methods for analyzing language input, child engagement states, and gesture typically focus on parts of the whole, whereas the current approach brings all three dimensions into alignment. Clinicians can use this framework as a lens for examining and enriching properties of caregiver input that promote early word learning for children with neurogenetic disorders.

Conflict of Interest

The authors declare that this research was supported by grants from the National Institute on Deafness and Other Communication Disorders (1R21DC017800–01A1) and the Center on Health, Aging, and Disability's Pilot Grant Program at the University of Illinois at Urbana-Champaign.

Acknowledgments

This research was supported by grants from the National Institute on Deafness and Other Communication Disorders (1R21DC017800–01A1) and the Center on Health, Aging, and Disability's Pilot Grant Program at the University of Illinois at Urbana-Champaign. We would like to thank Jana Iverson for her assistance in developing our child and maternal gesture coding schemes and Daniela Fanta Alarcon and Madison Larocca for assisting in coding child engagement.

Financial Disclosure

No relevant relationships exist for either author.

Nonfinancial Disclosure

No relevant relationships exist for either author.

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Artikel online veröffentlicht:
26. Juli 2021