HANDEDNESS AND COGNITIVE-ABILITIES IN A R EPRESENTATIVE SAMPLE OF ADOLESCENTS 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 include d other measures of laterality as well. We found, as Annett did, that strong right-handedness was associated with a weak left hand rather th an a strong right hand. However, we could not confirm two other predic tions bt the rst with our data: The nonverbal IQ was significantly low er 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 kin ds of grouping for handedness. We could not find the linear decline in nonverbal IQ from the left to the right extreme of handedness as pred icted by the rat. In spelling, too, there was a rather small, but sign ificant effect of handedness, explaining 2.4% of the variance. Spellin g in the first (left most) quartile of handedness was worse than in qu artiles two and four. The predicted poorer spelling in the extreme gro ups than in the middle groups (inverted U) was not found in our sample . Tn multivariate analysis with variables explaining larger proportion s of the variance in spelling (education, nonverbal IQ and sex) the sm all effect of handedness on spelling completely disappeared. A weak re lationship 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 rat are discussed.