1. Blinded octopuses were trained to discriminate by touch between rough and smooth spheres, using the arms on one side only.
2. Intact octopuses learned more rapidly than animals with the supraoesophageal brain split by a longitudinal cut.
3. With the brain split before training no side-to-side transfer occurred. Animals operated upon in this way did not discriminate when tested on the untrained side.
4. When intact octopuses were trained on both sides each side appeared to benefit from the experience gained by the other. The effect was difficult to evaluate because most of the errors in the experiments were due to taking the ‘negative’ object, with the result that raising the rate of training itself tends to improve performance by lowering the proportion of takes.
5. Animals trained on one side and then split continued to discriminate on the trained side, though at a reduced level of accuracy. When tested on the untrained side the performance of these animals was variable, depending upon the exact position of the split. The best scores were made by octopuses with some trained-side tissue left in contact with the test side. Animals with exactly medial cuts continued to discriminate, though at a reduced level of accuracy. Octopuses with the untrained side damaged did not discriminate at all.
6. Side-to-side transfer of the effects of tactile training can occur within the inferior frontal system. It can also be demonstrated to occur elsewhere in the supraoesophageal brain if the inferior frontal system has been split. Presumably this other pathway passes through the superior frontal/vertical lobe system.
7. These results are considered in relation to visual experiments on interocular transfer and it is concluded that memory traces are established on both sides of the brain as a result of unilateral training.