The Relationship Between Nonverbal Intelligence and Geschwind Scores in Left-Handed Subjects

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Abstract
Under psycho motor hypothesis, the relationship between left-handedness and nonverbal intelligence was studied in left-handed male and female subjects. Handedness was assessed by the Edinburgh Handedness Questionnaire; Geschwind scores (GS) were calculated for each subject. A GS of - 100 indicated consistent left-handedness. Spatial reasoning (nonverbal intelligence) was assessed by the Cattle's Culture Fair Intelligence Test. In the male and female subjects, the IQs increased for GSs from weak up to moderate left-handedness (GSs: -5 to -60), and decreased from moderate up to strong left-handedness (GSs: -60 to -100) linearly; the regression coefficient were found to be statistically significant. Weak-, and strong left-handedness both were associated with lowest scores; the highest scores were found in the subjects with moderate left-handedness (GSs: -55 to -65). It was concluded that the prerequisite for well-developed spatial reasoning should be two-sided development of the brain instead of one-sided dominance, and well functioning parallel processing between two cerebral hemispheres.

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