Can group differences in hemispheric asymmetry be inferred from behavioral laterality indices?

A large and often contradictory literature purports to demonstrate different patterns-or at least different degrees-of hemispheric specialization across various groups of people. Schizophrenics, dyslexies, stutterers, musicians, Orientals, Jews, and many other groups have been alleged to display idiosyncratic laterality patterns. An examination of this literature reveals three important problems. First the groups concerned are rarely homogeneous. This makes it difficult to know which group characteristics, if any, are responsible for the observed differences. Second, most behavioral laterality indices are of low reliability making group differences highly unstable. Third, the validity of many behavioral laterality indices has not been substantiated. Because of these problems, it is concluded that caution should be exercised in using and interpreting laterality measures to make between-group comparisons. For now at least, group differences in laterality cannot be inferred.