Intermanual transfer in the monkey as a function of amount of callosal sparing.

The effects of commissure section, task difficulty and overtraining on the intermanual transfer of tactile learning have been examined. Twenty-one rhesus monkeys were allocated to 4 groups. One group was subjected to complete transection of the corpus callosum, massa intermedia and posterior commissure. Some of this group also sustained a cerebellar section. A second group received a similar division of the commissures but with part of the posterior body of the corpus callosum left intact. A third group received similar division of the commissures but with the posterior commissure left intact. The fourth group formed an unoperated control group. Animals with only the posterior commissure left intact showed little or no transfer. Animals with partial callosal lesions showed significantly greater transfer than animals with total transections, but were impaired relative to the unoperated controls. Estimates have been made of the number of callosal fibres left intact in the animals with partial callosal lesions. These estimates have been correlated with transfer. The correlation was significant on only one task. Neither task difficulty nor overtraining were found to affect transfer significantly. The comparison of transfer of the submodalities of size and roughness was inconclusive.