Visual Responses by Octopus to Crabs and Other Figures Before and After Training

Abstract

Octopuses were fed for some days with fishes in their homes at one end of the tank, and the effect of figures shown at the opposite end was tested. Any small moving object may then be attacked, but the probability of attack is low and the delay long. Crabs and a black horizontal rectangle were attacked more often than other figures. If a figure is withdrawn on the occasions when it is attacked, then the probability of attacks remains low and may slowly decrease. If the octopus is allowed to eat crabs the probability of attacks on them quickly rises towards unity. If food is given when some other figure (say a black vertical rectangle) is attacked, then this figure will later be attacked. An octopus makes attacks more regularly on a figure that has recently been associated with food than on any other figure. This learning to attack a given figure can take place after removal of most of the vertical lobe, but the learning is slower and responses less accurate than in the normal animal. Octopuses from which the vertical lobe has been removed attack crabs more readily than other figures. The system that ensures attack therefore resides elsewhere, probably in the optic lobes. If shocks are given when a previously neutral figure is attacked, then the probability of further attacks on this figure rapidly approaches zero. Attacks on other figures or crabs remain frequent. If the vertical lobe is then removed, no attacks are made on such an originally neutral figure. If a figure that has been associated with food is then rewarded with shocks, the probability of attack falls more slowly than if the figure had been neutral. If the vertical lobe is now removed, the frequency of attacks rises. The memory preventing attack is therefore partly resident in the vertical lobe. The greater the amount of previous training to attack, the more slowly does the animal learn not to attack. This applies also if the training to attack is given after vertical lobe removal. After vertical lobe removal, shocks given when crabs are attacked rapidly reduce the probability of attack if the octopus had not previously eaten crabs while in the laboratory. If such feeding had taken place, the probability of attack falls only slowly without the vertical lobes. The experiments show that information stores associating a given figure with either food or shock can be set up after removal of the vertical lobes but tend to dissipate more rapidly than in a normal octopus.