Differences in language performance in variations of lateralization

Language proficiency was studied in 489 primary-school-aged children classified as extreme left-, extreme right-, mild left-, and mild right-handers on the basis of both hand-preference and hand-skill, using a test battery of seven measures. An ANOVA run on factor scores showed neither significant association of language proficiency with variations of lateralization regarding hand-preference and hand-skill nor differences in factor structure derived from a principal component analysis between extreme vs. mild hand-preference and hand-skill groups. Moreover, low language proficiency was not significantly associated with specific patterns of lateralization in hand-preference subgroups. In contrast, low language performers with poor hand-skill were significantly overrepresented both in the extreme left-handed group alone and when combined with the extreme right-handed, in comparison to mild left- and mild right-handed with respect to population. The data are not consistently accommodated by the theory of balanced polymorphism (mainly Annett, 1978, 1985 Annett & Manning, 1989 ). Alternately, factors such as lag of maturation ( Bishop, 1980, 1984, 1990a, 1990b ), delay of growth ( Geschwind & Galaburda, 1985b ), and developmental instability associated with unique patterns of variations in lateralization ( Yeo, Gangestad, & Daniel, 1993 ) are discussed as possible factors accounting for the present results.