Intermodal Stimulus Generalization and Retention of Habituation in Earthworms

Abstract

50 mature earthworms (L. terrestris) were assigned randomly to one of five stimulus conditions in an experiment with three phases. In Phase I Group Light-Vibration-Light received 2-sec. presentations of white light (with an 18-sec. intertrial interval) to an habituation criterion; in Phase II vibration was presented on the same schedule; and in Phase III, which began 2 hr. after the end of Phase I, presentations of light were given. Group Vibration-Light-Vibration received vibration in Phases I and III and light in Phase II; Groups Vibration-Rest-Vibration and Light-Rest-Light received no stimulation in Phase II. A control group was observed on the same schedule but received no stimuli. Results indicated that previous habituation to one stimulus reduced responses to the other stimulus, regardless of the type of stimulation (stimulus generalization). Retention of habituation from Phase I to Phase III was reduced in Group Light-Vibration-Light but not Group Vibration-Light-Vibration, relative to their counterparts receiving rest in Phase II. Thus results indicated that the effects of habituation in this organism depend on the presence of stimuli from other modalities.