The repository includes the data, scripts, LENA recording instruction and recording log used in running the experiment. The content of each folder is described below: Data: Data files necessary to run the scripts are in this folder. If you attempt to run the scripts on a local machine, denote the location where these files are downloaded as it must be specified in the Rmd script if the data is saved in a different location than the Rmd script. - _all.txt: This file includes sounds recorded for all participants using LENA device and vocal outputs are segmented using automated algorithm developed by LENA. This file is required to run the .Rmd file in the Scripts folder. - cdi_data_contingency.csv: This file includes important information such as CDI scores and contingency-related response counts. This file is required to run the .Rmd file in the Scripts folder. - female_WG_CDI_comprehension_norms.csv, female_WS_CDI_production_norms.csv, male_WG_CDI_comprehension_norms.csv, male_WS_CDI_production_norms.csv: These files include CDI norms for the Korean population. This file is required to run the .Rmd file in the Scripts folder to compute CDI percentile. Scripts: Contain a R-markdown file that can be run using the data files in the Data folder. - InitiatorEffect_Analyses.Rmd: This file includes the analyses presented in the manuscript. It requires all files in the Data folder to run. Models: Contain a HTML that can be open in a browser and a RData that can be loaded in R to check the analyses and models reported in this study. Given that refitting the models using the R-markdown file could be time-consuming, this serves as a quick starting point for easily examining the finding.s - InitiatorEffect_Analyses.html: HTML version of R-markdown file that show the results output from the script. - InitiatorEffect.RData: This file includes the raw data and any changes made during data cleaning process, as well as all models that were previously computed. LENA Recording Instruction.pdf: Korean instructions provided for correct use of the LENA device. Recording log.pdf: This is the log that mothers have to fill in with hourly activities and special notes to track children activities throughout the day of using LENA device.