Delayed Responses in Octopus

Since Hunter's (1912) original experiment with rats, it has been shown that many animals can learn to choose correctly between identical shapes even though the signal indicating the correct choice is removed before the animal is allowed to make the choice. The period during which an animal can be kept waiting after the signal has been removed and still make the correct choice varies from species to species and with the conditions (Konorski, 1959). It is difficult to judge the significance of these differences since the experimental situation is usually different in each species tested. The times vary from 5 to 10 sec. in rats to several hours in some primates. The cephalopods possess relatively and absolutely larger brains than any other invertebrate, and many experiments have demonstrated the ability of Octopus to learn to attack one of a pair of shapes and to avoid the other. The only experiments that have so far considered the capacity of the octopus to make a delayed response are those of Schiller (1949). He concluded that correct performance was correlated with the maintenance of bodily orientation during the time for which the animal 'remembers' the correct direction. In the present experiment the animals were shown two identical shapes, one of which had been accompanied by a crab. The crab was then removed and after a fixed time the octopus was allowed to attack the shapes. The situation allowed for a disturbance to be introduced during the delay period, in order to disturb the 'bodily orientation'.