[Handedness and cognitive abilities: findings in a representative sample of adolescents and young adults].

Handedness and cognitive abilities in a representative sample of adolescents and young adults. The relationship between laterality and cognitive ability was examined in a representative sample of adolescents and young adults between 16 and 30 years of age. The study was designed as a possible replication of Annett's data supporting her right-shift theory (rst), but included other measures of laterality as well. We found, as Annett did, that strong right-handedness was associated with a weak left hand rather than a strong right hand. However, we could not confirm two other predictions of the rst with our data: The nonverbal IQ was significantly lower in both extreme groups of handedness than in the two middle groups. Because of the sample size this rather small effect, explaining only 1.9% of the variance, is significant, but it disappears with other kinds of grouping for handedness. We could not find the linear decline in nonverbal IQ from the left to the right extreme of handedness as predicted by the rst. In spelling, too, there was a rather small, but significant effect of handedness, explaining 2.4% of the variance. Spelling in the first (left most) quartile of handedness was worse than in quartiles two and four. The predicted poorer spelling in the extreme groups than in the middle groups (inverted U) was not found in our sample. In multivariate analysis with variables explaining larger proportions of the variance in spelling (education, nonverbal IQ and sex) the small effect of handedness on spelling completely disappeared. A weak relationship between left-handedness and dyslexia was evident only with the strictest definition of dyslexia, regardless of how handedness was defined. The implications of these data for the rst are discussed.