README: Early, typical, and late talkers: an exploratory study on predictors of language development in the first two years of life 

https://doi.org/10.5061/dryad.wwpzgmsrb

We aim to investigate, between the 3rd and the 18th month of age, which interactive behaviors best predicted the probability to be at 24 months old a typical, late, or an early talker, and at which time point this may occur. If early intervention is to be provided in the critical period for language development, it is necessary to investigate and identify early predictors in younger children as early as possible. Hence the goal of the present study is to add information on an evolutionary period sparsely considered in the extant literature, and that is the study of developmental trajectories of early and late talkers starting from early months. 

This study included 30 monolingual Italian mother–child dyads. The dyads were selected from a larger and longitudinal study on parenting and infant development in Italy at University of Chieti before the lockdown due to Covid-19. The vocabularies of 10 late talkers (LT), 10 typical talkers (TT) and 10 early talkers (ET) were selected out of a pool of 80 MB-CDI forms (Caselli, Bello, Rinaldi, Stefanini, & Pasqualetti, 2015) completed by parents for children (42 males and 38 females) aged 24 months. Specifically:

LT (9 males and 1 female) produced less than 50 words (M = 37; range: 15-59), corresponding to the 10th percentile of productive vocabulary size,

ET (2 males and 8 females) produced more than 500 words (M = 562, range: 509-640), corresponding to the 90th percentile of productive vocabulary size,

TT (4 males and 6 females) produced around 225 words (M = 290, range: 222-350), and their vocabulary size was closer to the 50th normal mean value.

The dataset contains the transcription of 2 trained transcribers,working independently one from the other and using CHAT (CHILDES system) format (MacWhinney, 1991), transcribed all the interactive behaviors at 3, 6, 9 and 12 months directly from the mother – child recorded interaction. The second transcriber was not informed of the subject’s group assignment until the transcription was completed. The interactive behaviors were coded with a multi-dimensional schema:

Vocal productions. Each production was counted as a single unit of analysis when separated by at least one second. Crying vocalizations and sounds of discomfort were not considered. The frequency of the child’s vocal productions per minute was calculated. Child’s vocal productions were coded as follows: vocalization (vowel sound typically produced open-mouthed), grunt (consonant sound produced by closed or semi closed mouth), onomatopoeia (sounds that reproduce the sound of animals, or the noise produced by vehicles or actions), babbling (syllabic sound consisting of a consonant and a vowel), proto words (sounds similar to words that take on specific meaning in certain contexts).

Gaze at mother’s face. The unit of analysis corresponds to a child’s gaze at mother’s face. Every time that the child looked at the mother’s face, the gaze was coded. Gaze at the mother’s body, hair, hands, and gaze to environment was not considered. The frequency of child’s gaze at mother’s face per minute was calculated. 

Gestural productions. The unit of analysis corresponded to a child gestural production. Every gesture accompanied by other behaviors that signal the communicative intent (i.e., direct gaze to the interlocutor) was coded. The frequency of child gestural productions per minute was calculated. Gestural productions included deictic gestures: pointing (extending the index finger in the direction of an object, an event, or a person), giving (put an object towards the hand of the interlocutor), showing (put the object along the line of sight of the interlocutor). Moreover, we included representative gestures: iconic gestures (gestures which refer to objects, persons, or events, reproducing physical or functional characteristics), conventional (gestures with a culturally defined meaning and form e.g., waving bye, asking for silence pressing the index finger against the lips).

Reliability

Transcription reliability was calculated on 25% of the total videos. Point-by-point interactive behaviors comparisons were made, and the intercoder reliability ranged from 0,80 to 0,95. To maintain data consistency, only the material produced by the first transcriber was used for the final analysis. Inter-rater reliability for each predictor was computed by having a second rater that independently scored the subject performance on each measure. The inter-rater reliability was coded on 10% of the sample; the inter-coder reliability ranged from 0.83 to 0.94. Disagreements were solved with discussion to identify a unique score.

Interactive Behaviors in the second year of life

The interactive behaviors in the second year of life at 15-, 18- and 24-months were assessed using the scores assigned by parents at the CDI. Specifically, we considered:

CDI Actions and Gestures. We considered the number of actions and gestures produced by the child reported by the mother at 15 months. This category included communicative gestures, games and routines, actions with objects, symbolic game (i.e., pretending to be mom or dad, imitating the actions of the adult, and playing pretend with objects). Data was missing for a male in the LT group for CDI actions at 15 months.

CDI Productive and Receptive Vocabulary Size. We considered the receptive vocabulary size of the child (the number of words understood by the child) as reported by the mother at 15 and 18 months. At 24 months, we considered the productive vocabulary size (the number of words produced by the child) which was used as a criterion for inclusion in one of the 3 groups (late, typical, and early talkers). The CDI Receptive vocabulary measure at 18 months was missing for two children in the LTs group (1 male, 1 female) and one female in the ETs group.

Description of the data and file structure

The dataset contains 2 sheets. The first sheet is named “language child”. This sheet contains the child interactive behaviors coded by the transcribers during the mother-child interactions, and the MCDI data. In the second sheet the legend refers to the cell “group” in sheets 1 and 2 when 1 is early 2 is typical and 3 late.

Interaction duration in sec 3months: seconds of interaction between mother and child

• Interaction duration in sec x months: seconds of interaction between mother and child
• Vocalizations at x months: number of vocalizations by the child during the interaction
• Gestures x months: number of gestures by the child during the interaction
• Words x months: number of words by the child during the interaction
• Sounds 12 months: number of vocal sounds made by the child during the interaction
• Nouns 12 months: number of nouns produced by the child during the interaction
• People 12 months: number of name of people produced by the child during the interaction
• Routines 12 months: number of name of routines produced by the child during the interaction
• Functors 12 months: number of name of functors produced by the child during the interaction
• Comprehension 15 months: number of words comprehended by the child during the interaction
• Sounds 15 months: number of vocal sounds made by the child during the interaction
• Names 15 months: number of nouns produced by the child during the interaction
• People 15 months: number of name of people produced by the child during the interaction
• Predicates 15 months: number of name of predicates produced by the child during the interaction
• Adverbs 15 months: number of adverbs produced by the child during the interaction
• Functors 15 months: number of name of functors produced by the child during the interaction
• Deictic gestures 15 months: number of name of deictic gestures produced by the child during the interaction
• References 1 5months:number of references produced by the child during the interaction
• Routines 15 months: number of name of routines produced by the child during the interaction
• Fiction 15 months: number of fiction actions produced by the child during the interaction
• Imitation 15 months: number of imitative actions produced by the child during the interaction
• Fiction objects 15 months: number of fiction actions with objects produced by the child during the interaction
• AeG 15 months: actions and gestures produced by the child during the interaction
• Comprehension 18 months: number of words comprehended by the child during the interaction
• Routines 18 months: number of name of routines produced by the child during the interaction
• Actions 18 months: number of name of actions produced by the child during the interaction
• Fiction 18 months: number of fiction actions produced by the child during the interaction
• Imitation 18 months: number of imitative actions produced by the child during the interaction
• Fiction objects 18 months: number of fiction actions with objects produced by the child during the interaction
• AeG 18 months: actions and gestures produced by the child during the interaction
• Sounds 24 months: number of vocal sounds made by the child during the interaction
• Names 24 months: number of nouns produced by the child during the interaction
• People 24 months: number of name of people produced by the child during the interaction
• Routines 24 months: number of name of routines produced by the child during the interaction
• Predicates 24 months: number of name of predicates produced by the child during the interaction
• Adverbs 24 months: number of adverbs produced by the child during the interaction
• Functors 24 months: number of name of functors produced by the child during the interaction
• Production 24 months: number of words produced by the child during the interaction