Split decisions: problems in the interpretation of results from commissurotomized subjects

It has been widely accepted that there is little if any interhemispheric transfer of perceptual information in subjects following section of the forebrain commissures, although there may be diffuse transfer of emotional and connotative information, and an ability to direct spatial attention between hemispheres. However Sergent has recently shown that split-brained subjects can make rapid and accurate perceptual judgments based on visual stimuli presented simultaneously to the two visual fields. These include judgments of alignment, judgments of relative quantity, and higher-order judgments such as lexical decisions about letter strings straddling the visual fields. However it is premature to conclude that these tasks are accomplished by subcortical transfer of perceptual information; at least some of them can be explained in terms of strategies based on information available to just one hemisphere, or on the transfer of rudimentary information, perhaps accomplished through cross-cueing.