Abstract
Octopuses (Octopus vulgaris) are generally considered to possess extraordinary cognitive abilities including the ability to successfully perform in a serial reversal learning task. During reversal learning, an animal is presented with a discrimination problem and after reaching a learning criterion, the signs of the stimuli are reversed: the former positive becomes the negative stimulus and vice versa. If an animal improves its performance over reversals, it is ascribed advanced cognitive abilities. Reversal learning has been tested in octopus in a number of studies. However, the experimental procedures adopted in these studies involved pre-training on the new positive stimulus after a reversal, strong negative reinforcement or might have enabled secondary cueing by the experimenter. These procedures could have all affected the outcome of reversal learning. Thus, in this study, serial visual reversal learning was revisited in octopus. We trained four common octopuses (O. vulgaris) to discriminate between 2-dimensional stimuli presented on a monitor in a simultaneous visual discrimination task and reversed the signs of the stimuli each time the animals reached the learning criterion of ≥80% in two consecutive sessions. The animals were trained using operant conditioning techniques including a secondary reinforcer, a rod that was pushed up and down the feeding tube, which signaled the correctness of a response and preceded the subsequent primary reinforcement of food. The experimental protocol did not involve negative reinforcement. One animal completed four reversals and showed progressive improvement, i.e., it decreased its errors to criterion the more reversals it experienced. This animal developed a generalized response strategy. In contrast, another animal completed only one reversal, whereas two animals did not learn to reverse during the first reversal. In conclusion, some octopus individuals can learn to reverse in a visual task demonstrating behavioral flexibility even with a refined methodology.
Highlights
During reversal learning, an animal has to discriminate between two stimuli
Behavioral flexibility and the ability to learn more than a mere associate of inhibitory and excitatory reactions to two stimuli as shown when an animal is successful during reversal learning experiments is commonly associated with advanced cognitive abilities (Shettleworth, 1998) beyond mere discrimination learning
Four octopus individuals were trained on a serial visual reversal learning experiment as a first proof of concept of the new methodology
Summary
An animal has to discriminate between two stimuli. after successfully responding to one stimulus with a high performance, the animal has to switch its response pattern because the stimuli will be redefined. In a serial reversal learning experiment, the signatures of the stimuli are changed repeatedly every time the animal reaches a specific performance level. The way an animal solves a serial reversal learning experiment tells the experimenter if it has learnt stimulus specific responses or if it has learned to learn (Harlow, 1949; Shettleworth, 1998). The latter would be clear if the animal adopted a win-stay/looseshift strategy, which could lead to the optimal performance of only one error after a reversal has taken place. Behavioral flexibility and the ability to learn more than a mere associate of inhibitory and excitatory reactions to two stimuli as shown when an animal is successful during reversal learning experiments is commonly associated with advanced cognitive abilities (Shettleworth, 1998) beyond mere discrimination learning
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