ABSTRACT
Human information processing capacities are the product of a highly adaptive and versatile nervous system that provides individuals with various alternative means for representing, and operating on, information about the world. This versatility and adaptivity can be partly attributed to the conformation of the brain whose two hemispheres are not functional duplicates of one another but are endowed with their own specific skills, thus increasing the brain’s processing capacities while avoiding potential conflicts that would result from promiscuity. Evidence for such a functional hemispheric asymmetry has accumulated for more than a century through the study of neurological patients with damage to one or the other hemisphere, and it has recently been supplemented by research on neurologically intact subjects through the use of techniques allowing an initial segregation of the input to one side or the other of the brain. One such technique is based on lateral tachistoscopic presentation and takes advantage of the anatomical organisation of the visual system whereby the left hemiretinae of both eyes project to the left hemisphere and the right hemiretinae to the right hemisphere. By restricting stimuli to only one visual field, one may determine which of the hemispheres must initiate cerebral processing, and by observing the manner in which responses to various types of stimuli differ for right and left visual field presentations, one may make inferences about the functional asymmetry of the two
hemispheres. The general validity and reliability of this technique have been suggested by its capacity to produce results in broad agreement with findings from unilaterally brain damaged patients as well as to discriminate group-performance of left-and right-handed subjects who typically differ in their respective cerebral organisation (e.g., Corballis, 1983). The relative ease with which tachistoscopic experiments can be implemented, together with the view that knowledge becomes more secure through the convergence of differing lines of evidence, has thus contributed to making visual laterality studies one important source of information about functional cerebral asymmetry.
