Because hemiinattention is most commonly caused by right parietal lesions, it is possible that the left hemisphere attends to contralateral stimuli whereas the right attends to both contralateral and ipsilateral stimuli. We gave lateralized visual stimuli to 12 normal subjects and recorded the electroencephalograms. Desynchronization was determined by comparing the alpha power 1 second before and 1 second after a lateralized visual stimulus. Although the left parietal lobe desynchronized most after right-sided stimuli, the right parietal lobe desynchronized equally after right or left stimuli. These findings support the hypothesis that the right hemisphere is dominant for attention.

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Monkeys trained to perform with the extremity contralateral to a stimulus had unilateral neglect induced by a parietotemporal lesion. Their performance was normal postoperatively when stimulated on the side contralateral to the lesion, but they made errors when stimulated on the normal side (the side ipsilateral to the lesion), often failing to use the extremity on the neglected side (the side contralateral to the lesion). Although we expected parietotemporal lesions to induce sensory neglect (failure to respond to contralateral stimuli), we could show only that these animals had a defect of intention (contralateral hypokinesia). In this respect, neglect induced by parietotemporal lesions is similar to that induced by frontal or medial thalamic lesions.