Intellectual Differences in Relation to Personal and Family Handedness

Abstract

Right, mixed and left-handed college students were given the complete WAIS, and a series of cognitive factor tests. Results showed left- and mixed-handed individuals to have a significantly lower full scale I.Q. than right-handers. There was no difference between the mixed and left-handers. In all three handedness groups, subjects with a positive family history of sinistrality had a lower full scale I.Q. than did subjects without left-handed relatives. Neither handedness nor family history differentially affected the Verbal or Performance subscales, nor did they have a significant effect on scores in the other cognitive tests. These results are discussed with respect to Levy's theory of hemispheric specialization, and to the role of inheritance and brain damage in the causation of left- and mixed-handedness.