Slow processing in DLD (Zapparrata et al., 2023)
Purpose: Individuals with developmental language disorder (DLD) often exhibit slower processing on time-based tasks in comparison with age-matched peers. Processing speed has been linked to various linguistic skills and might serve as a global indicator of individual differences in language abilities. Despite an extensive literature on processing speed in DLD, it remains unclear whether slower processing is domain general or restricted to linguistic and/or auditory tasks.
Method: This meta-analysis used robust variance estimation to compare response/reaction times (RTs) of DLD and age-matched groups (N = 812 DLD, 870 neurotypical; Mage [DLD] = 8.9 years, range: 4.3–22.7 years). Moderators included task (simple RT, choice RT, naming, congruent/baseline conditions of interference control tasks), stimulus type (linguistic/nonlinguistic), stimulus modality (auditory/nonauditory), and response modality (verbal/nonverbal). Age and publication year were covariates.
Results: The overall effect based on 46 studies and 144 estimates indicated longer mean RTs in DLD groups (g = .47, p < .001, 95% CI [.38, .55]). Moderator analyses indicated larger effects when tasks required verbal as opposed to nonverbal responses. No other moderators approached significance. All subgroup analyses were significant, indicating longer mean RTs in DLD groups across tasks, stimulus types, stimulus modalities, and response modalities.
Conclusions: Individuals with DLD exhibit longer RTs across verbal and nonverbal tasks, which may contribute to observed difficulties in language, motor skills, and executive functioning. Simple processing speed measures should be included in screening for language delays but may not be suitable for differential diagnosis, given that slower processing may occur across multiple disorders.
Supplemental Material S1. Spreadsheet of each effect with the following information: sample sizes, mean ages, % male for each group (DLD and typically developing), the language profile and nonverbal IQ for the DLD group, the diagnostic label and method of diagnosis for language impairment, and descriptions of the task, task condition, and stimulus.
Supplemental Material S2. Text file that includes the search strings used in each database and other information about the systematic search process of the manuscript.
Supplemental Material S3. The full data set, with outliers included, is the data set that is read into and described in the R script for analysis.
Supplemental Material S4. The dataset with outliers removed is the data set that is read into and described in the R script for analysis. It is identical to the full data set, except the outlying effects are removed from this data set.
Supplemental Material S5. The R script with embedded instructions for the analysis contains the comprehensive script for the entire statistical analysis reported in the manuscript. The R packages used for the analysis are mentioned in the results section of the manuscript and can be accessed through their reference in the reference section.
Supplemental Material S6. Forest plot of all effect sizes, including outliers.
Zapparrata, N. M., Brooks, P. J., & Ober, T. (2023). Developmental language disorder is associated with slower processing across domains: A meta-analysis of time-based tasks. Journal of Speech, Language, and Hearing Research. Advance online publication. https://doi.org/10.1044/2022_JSLHR-22-00221