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

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 Questionaire; 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.

Key Words:

• handedness
• intelligence
• left-handedness
• lateralization
• manuel asymmetry
• man