Abstract: The "psychic tonus" model or PTM [1] of hemispheric
specialization states that the left hemisphere is a psychic and behavioral
activator and that the right hemisphere is an inhibitor. The PTM predicts that
the tonus of visual representation ought to manifest hemispheric specialization
in the occipital lobes. Specifically PTM predicts that pathological positive
visual tonus (visual hallucination) ought to be associated more frequently with
right occipital lesions. PTM also predicts that pathological negative visual
tonus (loss of visual imagery) ought to result more often from left occipital
lesions. We reviewed 78 cases of post lesion hallucination and 12 cases of post
lesion loss of evocation of images, all following a unilateral lesion. Analyses
of these relevant previously published cases support the predictions. In
accordance with previously published demonstrations of hemispheric
specialization for auditory tonus in the temporal lobes and for somesthetic
tonus in the parietal lobes, the present findings extend the psychic tonus
model of hemispheric specialization to vision in the occipital lobes.
