The mechanisms underlying the improved recall of isolated events (von Restorff effect) were investigated. Participants studied lists of stimuli containing a physical and a semantic isolate while performing a physical task or a lexical decision task. The physical-task group showed a physical but not a semantic isolation effect (IE) in free recall, whereas the lexical-decision group displayed both types of IEs. The recall of the isolates was independent of that of the other words, and isolates were usually reported separately from other words in the list. Event-related potentials recorded at encoding predicted the recall of both types of isolates. In recognition tests, the IE was obtained only when the encoding context was reinstated. These results are consistent with a model of the IE that stresses the role of the encoding processes immediately following the presentation of distinctive events, and that postulates interactions between these processes and subsequent elaboration of the stimuli.