THE systematic study of behavioural differences related to differential functioning of the cerebral hemispheres has increased markedly in recent years. The studies of Sperry and his collaborators1 on cerebral commissurotomy patients have stimulated many investigations into the hemisphere specialisations of normally functioning subjects. There are now many reports2,3 of statistically significant differences in hemisphere performance. Although hemisphere differences are consistent across independent experiments, they are small, occasionally inconsistent, and found within a limited experimental context, and so the generality of hemisphere differences remains to be established. We present here brief accounts of six experiments on cerebral lateralisation, four of which failed to find any differences and two which produced highly significant hemisphere differences. On the basis of this and published work, we believe that we can offer both a possible explanation for both the presence and absence of cerebral lateralisation effects in visual half-field experiments and also procedural guidelines that will produce cerebral lateralisation effects.
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