Individual Differences in Hemispheric Specialization: Sources and Measurement

Abstract

When we focus on individual differences in hemispheric specialization, we usually design our experiments to detect these differences as group effects. For example, we may include factors such as those listed in Table 1 in any particular study, and, of course, the list can be expanded at will. Although the factors must, for reasons of statistical analysis, be applied to groups of subjects, we often study them not because we are interested in groups of left handers, or schizophrenics, etc. per se, but rather because we want to make a statement about individuals. The individuals within the group are assumed (or hoped) to be alike on all other variables important for brain lateralization. For practical purposes, this is impossible since it would be impossible to form a group of subjects representing each intersection of all the factors listed. There are probably also sources of individual variation in lateralization tests that are beyond any divisions we have managed to make so far. With this perspective, each individual is seen to be a group unto himself to some extent. An intensive case study of the individual, although possible, and laudable (Dywan & Segalowitz, in press), would not satisfy our curiosity about the factors under examination (cf. Caramazza, 1986). We must remain with the traditional group paradigm, but we are left in the traditional, awkward position of having to accept the individual variation in lateralization not controlled for in our study as error variance.