Objective: Dyslexia is characterized by difficulties with accurate and şuent word reading and spelling. Speech-language impairment in preschool years places a child at high-risk of reading disorder, particularly if the child has low general cognitive ability. Moreover, nonverbal IQ was considered as a protective factor. Using neuropsychological measures, we aimed to study the effects of Verbal/Performance (V/P) IQ discrepancies and language-based skills on reading performance in dyslexia. Our hypothesis was that language-based measures would be correlated to the reading performance of children.
Method: Twenty five children (6 female) aged 7-15 years (mean age: 9.48±1.78) referred with reading difficulties to Marmara University Medical Faculty Hospital participated in the study. The neuropsychometric test battery of specific learning disability has been used to diagnose learning disorders, and K-SADS diagnostic interview has been used to screen psychopathology in subjects. The following skills of subjects have been evaluated neuropsychologically: Full Scale IQ with Wechsler Intelligence Scale For Children-Revised (WISC-R), selective attention with Stroop Task, lateralization dominance with Head and Harris scales, auditory/verbal, visual immediate and working memory with Digit Span and Visual Span subtests of Wechsler scales, Semantic Fluency with Category Naming Test, Phonetic Fluency with phonemic verbal şuency task, visio-spatial perception with Line Orientation Test, spatial attention and processing speed with Letter Cancelation. Statistical analyses were performed in two ways:
1) Subjects were divided into two groups according to verbal/performance IQ discrepancies (22 points were considered as cut-off) and groups were compared with t-test.
2) Correlation analyses were conducted to evaluate the relationship between reading performance and neuropsychological measures.
Results: Reading performance of subjects was not different between the groups, although reading comprehension scores were higher in high V/P IQ discrepant group. In the high V/P IQ discrepant group, VIQ was lower significantly (p=0.002); PIQ was higher significantly (p=0.003); total IQ was not different when compared to the low V/PIQ discrepant group. Similarities, vocabulary and comprehension subscale scores were higher in low V/P IQ discrepancy group (p=0.007, p=0.038, p=0.008 respectively). Object assembly subtest performance and line orientation scores were higher in high V/P IQ discrepancy subjects (p=0.009, p=0.02 respectively). Lateralization dominance scores were lower in this (high V/P discrepant) group (Head cross score: p=0.03 and Harris score: p=0.024). Correlation analyses revealed that reading performance of subjects were positively correlated with semantic and phonetic şuency, auditory working memory and processing speed (p=0.008, p=0.017, p=0.040, p=0.007 respectively). The count of inattentive symptoms were negatively correlated with the reading performance (p=0.015).
Conclusion: In line with our hypothesis, for this sample, reading performance was correlated to processing speed and language-based skills, semantic and phonetic şuency, verbal working memory performance. High V/P IQ discrepant group was associated with higher visio-spatial and comprehension skills but lower lateralization dominance. Not only language-based skills but other cognitive advantages and deficits would be considered in the evaluation and intervention process of these children.