Variation in Infant-Directed Speech Across Infant Development

Author’s Note

I joined Language Learning Lab at the Center for Mind and Brain and worked with Dr. Katharine Graf Estes as a research assistant from Spring 2023 to Spring 2024. Through this experience, I learned how to recruit participants for studies, study empirical papers critically, and build a solid foundation to understand the various projects that the Language Learning Lab is currently undertaking. I was recommended to apply for the Provost’s Undergraduate Fellowship and pursue a capstone project for my final year of undergrad. Inspired by our discussions in regards to infant language acquisition, I thought of investigating this topic through the data we have been collecting all year from the participants coming to our laboratory. After receiving my acceptance notice, I started my project as a PUF scholarship recipient. Last April 2024, I had the opportunity to present my research at the Undergraduate Research Conference. I hope that this initiative will also inspire future studies about language development that may explore the limitations found in this research study. I give all my appreciation to Dr. Katharine Graf Estes, Jenny-Jiaqi Geng, and Language Learning Lab at the CMB for their support and encouragement.
 

Introduction

How infants acquire language has been studied by researchers for a long time. Developmental psychologists particularly focus on the role caregivers play in facilitating their child’s language development. Research shows that adults have a distinct way of speaking to young children. Infant-directed speech (IDS), or parentese, is a speech style with prosodic features such as higher pitch, wider pitch range, shorter utterances, and more repetitions than adult-directed speech (ADS) (Fernald & Kuhl, 1987; Fernald & Simon, 1984). The distinction between IDS and ADS is fundamental in studying infant preference and its implications for language acquisition. Infants as young as one-month-old (Cooper & Aslin, 1990) and four-month-old newborns (Kaplan et al., 1995; Fernald, 1985) prefer IDS over ADS. Findings from multiple studies suggest that adults’ ability to capture and sustain infants’ attention while using IDS influences the time they spend attending to their caregivers’ speech, thus encouraging language processing in early development (Fernald, 1992; Golinkoff et al., 2015).

Furthermore, increased IDS exposure among infants later predicted efficient speech-processing skills and larger vocabularies by 24 months of age, more specifically when the speech is directed to the child rather than overheard (Weisleder & Fernald, 2013). After establishing that the usage of IDS indeed plays a role in language development, researchers turn to questions that examine how and which of its properties influence infant language acquisition. Exaggerated prosodic qualities in IDS may provide helpful cues for infants to recognize and divide speech into meaningful grammatical units (segmentation). Studies that investigated the relationship between children’s linguistic environment and their language acquisition found that infants were sensitive to segment-marking cues for IDS but not ADS (Nelson et al., 1989; Furrow et al., 1979). With evidence that babies are able to process word segmentation when listening to parentese, these findings may suggest that certain IDS properties provide additional lexical information that signals when words are semantically significant.

Repetition and Language Outcomes

Repetition is a feature of IDS (Snow, 1972) that is related to children’s language development. Infants between the ages of 4 to 6 months started to shift their attention from prosodic aspects (emotional cues) to the linguistic structure of IDS (repeated utterances). This finding may point to the underlying influence of IDS on the development of word segmentation skills that appear among young children after this stage of their language acquisition trajectory (McRoberts et al., 2009). Focusing on this specific IDS feature and its relation to children’s word learning process, Schwab and Lew-Williams (2016) found that repetition in fathers’ language input to 7-month-old infants is positively associated with children’s vocabulary size at 24 months. These findings are also supported by Newman, Rowe and Ratner (2016), who conducted a study examining maternal input (repetition) and their infant’s speech segmentation skills at 7 months, which also predicted the children’s language outcomes at 24 months. Parents’ role in children’s language acquisition through their use of IDS when communicating with their infants continues to be emphasized in these studies.

Current Study

The motivation for the current study is to examine when parents are more likely to repeat words or phrases when speaking to their infants—but instead of asking if parents change the way they interact with their children, we asked how and when parents change their behavior. Previous literature has explored this topic under different circumstances but there is not one notable conclusion widely accepted among researchers. The goal of this project is to understand the way parents structure their interactions in various conditions and contribute additional context across infant development.

Masur (1997) investigated if mothers adjusted their behavior of naming familiar and novel toy animals during play interactions with their infants. At the end of this longitudinal study, the researchers found that the mothers’ provision of novel animal names did not significantly change despite the number of animals considered novel having declined by the infants’ second year of life. On the other hand, the mothers’ references to familiar animal names increased as well as the number of animals considered familiar having increased at the end of the second year. Mothers’ sensitivity to their children’s knowledge is illustrated by the modification of their naming behavior based on the infants’ familiarity with the toy animals. Although the study’s conclusion on how this transformation can directly impact children’s lexical acquisition remains unclear, Masur (1997) findings emphasize the interactive nature of labeling practices among parent-infant dyads, which has also been hypothesized to be an important factor in infants’ preference of IDS (Schroer et al., 2019).

Chen et al. (2021) also explored early word learning in toddlers by observing dyadic interactions. Consistent with the results in Masur (1997), researchers found that parents were more likely to name familiar objects than novel objects. However, children’s attention was more synchronized with the parent’s labeling of novel objects, suggesting the possibility that parents are modifying naming behavior based on their child’s attentional state (Chen et al., 2021). Although the instances were few, the synchrony between parents’ naming of novel objects and the children’s looking behaviors are considered “higher quality of word-learning opportunities” because parents’ increased responsiveness during communicative social exchange with their infants have been previously discussed to promote language acquisition (Tamis-LeMonda et al., 2014).

In this study, we recruited parents and their infants to participate in a book reading and free play task in the laboratory. We recorded video and audio recordings of the participants completing both tasks. The parent-infant dyads were introduced to 12 animals that fall into three categories: book-only condition, toy-only condition, and book and toy condition. We asked two questions based on two specific contexts of this study: infants’ ages and animal conditions. We wanted to examine if repetition rates would differ across the infants’ age range. Are parents more likely to repeat to younger or older infants? Will parents repeat the animal names more while reading or playing with their children? We hypothesized that parents would repeat more to younger infants and the repetition rates will vary across task conditions. This study aims to expand the literature on the role of parent speech in facilitating children’s language development by studying dyadic interactions across multiple contexts and indicate where future research could explore specific contexts that will foster early learning.

Method

Participants

Participants were 46 parent-infant dyads (21 female infants, 38 mothers) and the babies’ ages ranged from 11-20 months old (M = 16.06, SD = 2.92). Infants ages 11-15 months were categorized as “younger” and infants ages 16-20 months old were categorized as “older.” Families were invited to the laboratory to participate in a book reading and free play study in person around the Davis, Woodland, Sacramento, and neighboring areas. To comply with the institute’s COVID policy at the time of data collection, parents and research assistants wore masks inside the building throughout the duration of the study. Monolingual and multilingual families were initially recruited for the study, but parents who did not use English animal names while interacting with their infants were excluded from the analysis of this research.

Procedure

Parents and their infants participated in two tasks alternating in order (22 dyads played with toys first, 24 dyads read books first). One free play session involved eight toy animals, while the other involved two animal-themed books. Overall, the parent-infant dyads were introduced to 12 animals categorized in three conditions: book and toy, toy-only, and book-only. The first set of animals were present in both tasks: cow, sheep, horse, and pig. The second set of animals were only present as toy animals: elephant, monkey, lion, and bear. The last set of animals only appeared in the books: duck, kitten, dog, and goat. Three cameras capturing the participants in third-person viewpoints recorded videos of the play and book sessions. The parents also wore a clip-on microphone that recorded their speech during the task. Parents were instructed to play with the toys and read the books with their child as they naturally would at home. Both play and toy tasks lasted for eight minutes, accumulating 16 minutes of session data to analyze per parent-infant dyad.

Analysis

To examine the parents’ linguistic input through the means of repetition as a measure of IDS, we used the audio recordings captured by the microphone worn by the participants to count how many times they repeated the 12 animal names. Each audio file from the dyads’ session was split in two files: book task and toy task (92 audio files overall). Using the automated transcription software, Sonix, we extracted text from the recordings and ran an analysis using an R script to count the number of target word repetitions during the tasks per participant. We predicted that parents would repeat the animal names more to younger infants than

older infants. As repetition supports learning new words (Schwab & Lew-Williams, 2016), we predicted there would be less repetition among older infants because they are able to recognize more words than younger infants. We also examined whether repetition rates would vary among parents based on the context of playing with toys versus reading books with their babies. We hypothesized that there will be a marked difference in the parents’ repetition of the animal names across the three conditions.

Results

All three conditions yielded significant results (Figure 1). Parents repeated the animal names the most when the animals were in both books and toys. This difference can be explained on the basis that the parents had two opportunities to name the animals in the book and toy condition. There was also a significant difference between the rates of the animal names repeated in the book-only (M = 19.6, SD = 9.8) and toy-only (M = 13.3, SD = 9.3) conditions which illustrates that parents repeated the animal names more when reading books than when playing with toys, t(45) = 3.79, p < .001. In addition, the total repetitions to female infants (M = 55.71, SD = 22.68) and male infants (M = 72.04, SD = 30.44) also demonstrated a significant difference, p = .05. We also calculated the correlation of total repetitions across ages and found no significant relationship between the number of target words repeated and the infants’ ages (Figure 2), which is different from our initial hypothesis that parents would be more likely to repeat to younger infants. 

Figure 1

Word Repetition Across Conditions

 

Note. This figure illustrates the t-test results that compared the rates of target words repeated per participant (represented by the dots on the graph) across conditions. After completing the analysis, we found significant differences in every comparison of the three sets of animal names. 

Table 1: Means and Standard Deviations for the Three Conditions

Figure 2

Total Repetitions Across Infants’ Ages in Months

Note. This figure is a scatterplot that visualizes the lack of correlation between the overall number of target words repeated by parents and the infants’ ages. Parents did not repeat the animal names more or less whether the infant was younger or older.

Discussion

The present study was conducted to investigate how parents modify their interactions with their infants by focusing on repetition as a measure of infant-directed speech input. Activities such as free play and book reading may generate word-learning opportunities for infants as they engage in linguistic interactions with their caregivers. In pursuit of understanding what aspects of caregivers’ labeling behavior might facilitate enhanced language acquisition, we designed this current research to identify differences in repeated utterances produced by parents in various contexts across infant development. Our findings expand the existing literature on parents’ role on infant language acquisition by identifying when and where they modified their labeling behavior (repetition) depending on the activity they are doing with their children.

We asked two questions: (a) Will the rates of the target words repeated by the parents differ across the three conditions we set in this study? (b) Will parents repeat the animal names less as the infant grows older in age? First, our results saw that parents repeated the target words more when reading books compared to when the participants played with toys. In relation to prior research, shared reading between parents and infants is related to enhanced language skills (Karrass & Braungart-Rieker, 2005). Our findings may suggest that repetition is one way parents support learning during reading, as they use more sophisticated vocabulary and language than when engaging in free play with their children. However, further investigation is necessary to clarify when the presence of this repetition, shared reading, or the quality of interaction will have significant effects on later language outcomes in terms of the trajectory of infant development.

Second, we wanted to answer if the number of target words repeated by parents was related to the infants’ ages. We found no significant relationship between the infants’ ages and the total repetitions. The same results were found when calculating for the other conditions as well. The age range of the participants in the sample was small which may have been a factor in the lack of significant correlation between age and repetition. McRoberts, McDonough and Lakusta (2009) included six-month-old infants in their sample of participants who showed notable preference for repetitive cues (a measure of IDS) which is considerably younger than the youngest infant in this current study at 11 months old. Repetition in IDS has been hypothesized “to prime the child’s ability to segment” (Newman et al., 2016). Furthermore, one study’s results showed repetition rates declining in relation to children’s vocabulary size, suggesting that “fathers whose children possessed larger vocabularies used less repetition” (Schwab et al., 2016). Future analyses may look to broaden the age range of the participants and potentially find significant differences in parents’ input in relation to the children’s later language outcomes.

Additionally, an interesting finding came up in this current investigation that offers a contrasting result with previous research in the context of infants’ sex difference. Previously, mothers of female infants were observed to repeat more than mothers of male infants (Masur, 1997). In this study, we found that parents of male infants in this sample significantly produced more repeated utterances compared to parents of female infants. Future research needs to be conducted to further establish the presence of infants’ sex differences in the context of caregivers’ naming practices.

Limitations

Repetition is one of multiple characteristics associated with infant-directed speech. Other prosodic and lexical features (pitch range, vowel articulation, utterance duration, etc.) that set this speech style apart from adult-to-adult communication may also offer a deeper and more complex insight to parents’ role in infant language acquisition. Another significant limitation of this study is the exclusion of multilingual contexts in the analysis. The use of IDS is not to be considered the sole standard and universal caregiver-infant experience (Cristia et al., 2019; Schieffelin & Ochs, 1983). Parental differences such as communication style, personality, and other measures of participants’ demographic information such as race, age, and social-economic status were also not considered in this research. Isolation of these factors might be a helpful starting point for the design of future studies in the context of infant language acquisition.

Conclusion

The topic of language acquisition will involve exploring the role caregivers play as infants’ primary communication partner in their first year of life. As previous research established that adults indeed modify their behavior in regards to their child’s growing linguistic knowledge, identifying where and how they change their actions is the next step in this investigation. This study illustrated how the significant difference between parents’ IDS modification across multiple contexts may point to how their input facilitates word learning during parent–child social interaction. We found that parents were more likely to repeat target words while reading books over playing with toys. Expanding the frame of reference concerning how parents structure their interactions with their children will guide the fundamental elements that will foster early language development. 

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