Learning of leg position in the shore crab,carcinus maenas

Decerebrate crabs were trained to raise their legs to avoid electric shocks. Compared with yoked controls, experimental crabs received significantly fewer shocks after 6–7 minutes training and also during the first minute of a subsequent testing period when both experimental and control crabs were in a training situation. There was considerable variation in the performance of different crabs. Some learned quickly, some slowly, while others did not learn at all. In some, the raised leg position was maintained without further reinforcement. In others, periods when the animal was receiving few shocks were interrupted by periods when the leg was lowered and several shocks were received. A variety of leg movements were utilised by crabs to avoid shocks, the most common being flexion at the mero‐carpopodite joint.