Changing hemisphere dominance by changing reward probability in split-brain monkeys.

The manifested dominance split-brain monkeys usually show for performing visual tasks through one hemisphere, when perceptual information is equally available to both, was analyzed. Three split-brain monkeys, each being trained similar yet different discriminations to each hemisphere, were allowed the opportunity to choose between the two problems when both were presented simultaneously. Initially all consistently preferred to respond with the right hemisphere. Subsequently, in separate training, the reward schedule for the dominant eye was advanced to FR-6 while the nondominant hemisphere was maintained on FR-1 or continual reward. Simultaneous exposure of the two problems now found the animals altering their original dominance and consistently performing through the nondominant hemisphere. The results are consistent with the view that attentional or preference processes, or both, are amenable to reward probability. Also, each half of the bisected brain can reliably keep different assigned reward values localized and specific to each hemisphere.