Hand laterality and cognitive ability: a multiple regression approach.

Several different associations between hand laterality and cognitive ability have been proposed. Studies reporting different conclusions vary in their procedures for defining laterality, and several of them rely on measures which are statistically problematic. Previous methods for measuring relative hand skill have not satisfactorily separated the overall level of hand skill, which is a known correlate of cognitive ability, from the asymmetry of its distribution. This paper uses a multiple regression paradigm that separates these two components. Support is found for Leask and Crow's [Trends in Cognitive Sciences, 5 (2001) 513] proposal that average cognitive ability increases monotonically with increasing strength of laterality, regardless of its direction. The small average advantage to dextrals stems from them being more strongly lateralised than sinistrals. The paucity of strong dextrals amongst the very gifted is due to a smaller variance in cognitive ability in this group.