Habituation of the polychaete Nereis to sudden stimuli. 1. General properties of the habituation process

Abstract

1. 1. The polychaete worm Nereis pelagica habituates most rapidly to repeated stimulation by a moving shadow, or by mechanical shock. It habituates less rapidly to a sudden decrease in light intensity and most slowly to a sudden increase in light intensity. 2. 2. The rate at which worms habituate to a sudden increase in light intensity is dependent upon the length of time the light remains switched on at each trial. It habituates most slowly when the light remains on for 30 per cent, of the time at each trial. 3. 3. Habituation becomes slower as the interval between trials increases. 4. 4. Habituation to a sudden increase in light intensity, with trials given at 3-minute intervals, persists for about 17 hours. If trials are given at 1 2 -minute intervals, habituation persists for about 5 hours. 5. 5. Habituation to a moving shadow is independent of habituation to mechanical shock, but habituation to a moving shadow and to a sudden decrease in light intensity are mutually interacting processes. Worms already habituated to one require a greater number of trials than usual before they become habituated to the other. Exposure to stimulation by a sudden decrease in light intensity maintains an already existing state of habituation to a moving shadow, though the reverse is not true. 6. 7. If the worms are repeatedly exposed to a stimulus too weak to evoke a visible response, they become partially habituated to a supraliminal stimulus of the same kind. 7. 8. Habituation is a function of the elicitation rate, is cumulative and impermanent in Nereis as in other animals. Generalization of habituation has not been observed.