Changes in Textural Preferences in Octopus After Lesions

Abstract

ABSTRACT Octopuses repeatedly tested at alternate trials with rough and smooth spheres presented without reward take more of the smooth than the rough spheres. The individuals that take most often show the greatest preference. The overall tendency to take decreases within each session of sixteen trials and recovers by the next session some hours later. There is a slight decrease in mean takes over the first few sessions but the level then remains at about 36% over ten sessions of sixteen trials. Animals without vertical lobes tested in the same way without rewards take more often (at 60% of all trials). As with the normals there is a decline in take within each session: Extinction is therefore not exclusively the result of changes in the vertical lobe. The preference for smooth is less marked in animals without the vertical lobes than in normals. Animals with the supraoesophageal lobes split by a vertical cut (‘half-brain animals ‘) and animals with the supraoesophageal lobes removed except for the buccal and ventral subfrontal take fewer objects than normal octopuses. The same animals show reduction or reversal of the smooth preference manifest in normal octopuses. Removal of the whole of the inferior frontal system produced animals that take more often than normal, at 63% of all trials. These octopuses showed a marked preference for smooth. The system for release of objects is defective in these animals and this may act to give the appearance of excesss of takes of smooth. The fact that blind but otherwise normal octopuses prefer smooth objects was confirmed in a discrimination training experiment. Normal animals trained with a smooth sphere as positive performed better initially than those trained in the other direction, though the asymptote reached was the same for both. Animals without vertical lobes showed in training about the same preference for smooth as normals but were variable. They learned more slowly than normals. Half-brain animals showed a strong preference for rough in training. The animals trained with smooth positive learned very slowly and had not reached the level of those trained with rough positive after 160 trials.