The significance of nonverbal performance in children with developmental language disorder

Nonverbal deficits are frequently reported in children with developmental language disorder (DLD). In the new diagnostic criteria of DLD, the previous requirement of normal nonverbal performance has been removed and children with below average and even weak nonverbal skills now fit under the DLD definition. However, the significance of the nonverbal cognitive level, and the connection between nonverbal and verbal skills in these children diagnosed according to the new DLD classification is unclear. In the present study, the significance of nonverbal cognitive level on verbal performance was investigated among preschool-aged children with remarkable deficits in language development. Verbal skills were compared between average, below average, and weak nonverbal cognitive level groups. The connection between nonverbal and verbal skills was evaluated with Pearson correlations, and the covariance structure of the subtests used was modeled with Structural Modelling. The connection between nonverbal cognitive level and verbal skills was clear; weaker nonverbal cognitive levels were associated with lower verbal skills. While receptive language skills and verbal short-term-memory (STM) were the most profound weaknesses, relative strengths emerged for each nonverbal cognitive level group in fluid intelligence, especially in nonverbal reasoning tasks without time limits. In addition, fluid intelligence was strongly linked to verbal understanding and reasoning. These results suggest that the relative strength in nonverbal fluid intelligence with specific weaknesses in receptive language, verbal understanding, and verbal STM could be used as basic factors differentiating children with DLD from those with intellectual disability.