Global processing speed in children with low reading ability and in children and adults with typical reading ability:...

To investigate processing speed as a latent dimension in children with dyslexia and children and adults with typical reading skills.

Exploratory factor analysis (FA) was based on a sample of multigenerational families, each ascertained through a child with dyslexia. Eleven measures--6 of them timed--represented verbal and nonverbal processes, alphabet writing, and motor sequencing in the hand and oral motor system. FA was conducted in 4 cohorts (all children, a subset of children with low reading scores, a subset of children with typical reading scores, and adults with typical reading scores; total N = 829).

Processing speed formed the first factor in all cohorts. Both measures of motor sequencing speed loaded on the speed factor with the other timed variables. Children with poor reading scores showed lower speed factor scores than did typical peers. The speed factor was negatively correlated with age in the adults.

The speed dimension was observed independently of participant cohort, gender, and reading ability. Results are consistent with a unified theory of processing speed as a quadratic function of age in typical development and with slowed processing in poor readers.