Comparing the Ability of Motor Simulation in Dyslexic and Typical Children during Action Verbs Processing

A key finding in embodied construction grammar (ECG) is that brain areas related to action and language are interdependent. Specifically, with regard to this idea, several studies have shown that action execution and observation influence subsequent language processing, in that action verbs processing elicit activation of effector-specific regions in primary motor and premotor cortex. However, the relationship between motor skills impairment and action related language processing is still a controversial issue. In order to clarify this issue, we designed image-verb matching task (Bergen et al., 2003) to examine motor imagery ability of children with dyslexia during action verbs comprehension. We used Persian verbs expressing hand and foot actions that were either congruent or incongruent with the images that had been presented.

Thirty four children from grades 2 through 6 (aged between 8 to 13 years old) participated in this study. A group of 17 children with surface dyslexia with mild to moderate degrees of reading disorder (12 boys and 5 girls; mean age= 10.6, SD= 1.51) and a group of 17 typically control children (12 boys and 5 girls; mean age= 10.3, SD= 1.41) were selected. In both groups the children were matched pairwise on chronological age and gender. Children with DD were recruited for participation through rehabilitation centers and special centers for language and learning disabilities. The TD group consisted of a subset of children who were recruited from state primary schools in the city of Shiraz. The diagnoses for dyslexics were based on several sources of information as 1) assessment by psychiatric specialist or teacher report, 2) intelligence test: Persian version of the Wechsler Intelligence Scale for Children (WISC-IV), subjects with IQ level below 80 were excluded, 3) Bender Visual Motor Gestalt test, and 4) informal interview with children and their parents. Potential subjects both in DD and control groups were screened to ensure they didnchr t have any history of neurological and psychiatric disorders that could contribute to motor impairment. In addition, subjects underwent reading examination to evaluate their reading skills and children who had severe reading disability were excluded. All participants were Persian-speaking monolinguals. Ethics approval was obtained from the Human Research Ethics Committee (IR.SUMS.REHAB.REC.1398.021) at SUMS. Before beginning the experiment, parents gave written consent for their children to participate in our study, which was approved by ethics committee at SUMS and they were all paid for participation.

The nonparametric Kruskal Wallis Test showed a significant effect of matching in image-verb verification task, and indicating a better performance of the control children over the dyslexic children; Matching verbs, (DD mean= 3.55, SD= 3.43; TD mean= 2.41, SD= 0.88, p<.001), same-effector mismatches (DD mean= 3.47, SD=1.98; TD mean= 3.32, SD=0.97, p<.001), and different-effector mismatches (DD mean= 4.03, SD=2.92; TD mean=2.43, SD=0.78, p<.001). The chi-Square test showed a better performance of the control children (DD mean=66%, TD mean=87.3%, p<.001) over the dyslexic children. In all verb types, dyslexics scored significantly less than typical children; Matching verbs, (DD mean= 71.8%; TD mean= 88.2%, p<.001), same-effector mismatches (DD mean= 59.7%; TD mean= 75.6%, p<.001), and different-effector mismatches (DD mean= 66.4%; TD mean= 97.9%, p<.001).

The findings reflect different nature of motor imagery used by TD and DD children and support the hypothesis that motor skill impairment affects motor imagery ability during action verbs processing. Furthermore, these findings indicate that action execution and action verbs processing share common representations and lend support to embodied cognition theory in that there is a significant connection between embodied experiences and language comprehension. Therefore, lower ability to simulate the motor representation of action verbs highlights the critical role of embodied experiences on language understanding.