Long-term habituation to a danger stimulus in the crab Chasmagnathus granulatus.

A shadow moving overhead acts as a danger stimulus and elicits an escape response in the crab Chasmagnathus granulatus, that habituates after 15 stimulus presentations at 3-min intervals. Here, the habituation was induced by 3 diverse shadow stimuli and the habituated response persisted after 24 hr in every case. This long-lasting effect failed to appear if the testing stimulus did not keep the same spatial specificity as that of the training one. A partial stimulus generalization was detected, when training and testing stimuli differed in size. The adaptive value of a high danger stimulus specificity in long-term habituation is discussed. Extinction of the long-term habituated response failed to occur although crabs were exposed to the context in the absence of danger stimulation.