1. In this paper the effects of vertical and superior frontal lobe removal are considered in relation to touch learning and discussed in the light of findings from visual experiments.
2. Removal of the vertical and/or the median superior frontal lobe slows touch learning. The operated animals take nearly twice as many trials as controls to learn a simple tactile discrimination. Their performance is more variable than that of controls.
3. Removal of these parts increases the number, but does not alter the sign of errors made. Removal of the median superior frontal does not appear to add to the effect of removing the vertical lobe.
4. The pattern of errors made by controls and experimental animals is similar within groups of massed trials given in the course of training.
5. Once trained to a given standard of accuracy (75 or 85% correct responses) the operated animals remember for as long as controls. Retention tests show little difference in performance 5 and 10 days after the end of training; the difference between controls and experimentals cannot be attributed to more rapid forgetting by the latter.
6. In experiments involving reversal of learned discriminations controls learn in fewer trials than experimentals.
7. Octopuses operated after training show an immediate decline in performance that can, to a considerable extent, be compensated by further training. The operations do not entirely remove the effects of past experience. Again, the effects are quantitative, not qualitative.
8. Octopuses with the vertical lobes removed take about six times as long as controls to examine and reject an unfamiliar object.
9. These results are considered in relation to (a) the effects of lesions to the inferior frontal and subfrontal lobes, which are anatomically similar to the superior frontal and vertical, and (b) current theories of the function of the vertical lobe in visual experiments.
10. It is concluded that the vertical lobe produces quantitative increases in the effects of experience on subsequent actions. It remains unestablished whether it does this by amplifying the effects of events taking place elsewhere in the central nervous system or by adding further units to a pool of neurones alterable by experience. The latter seems more probable in view of experiments on the anatomically similar sub-frontal lobe, where a minimal number of cells must be present if the animals are to learn at all.