The generation effect, in which items generated by following some rule are remembered better than stimuli that are simply read, has been studied intensely over the past two decades. To date, however, researchers have largely ignored the temporal aspects of this effect. In the present research, we used a variable onset time for the presentation of the to-be-remembered material, thus providing the ability to determine at what point during processing the generation effect originates. The results indicate that some benefit from generation attempts occurs even when subjects have only a few hundred milliseconds in which to process the stimulus, but that more of the benefit occurs later. This finding suggests that the generation effect results from continuous or multiple discrete stages of information accrual or strengthening of memory traces over time, rather than from a single discrete increment upon final generation.The generation effect, first described by Slamecka and Graf (1978), is a robust phenomenon in which recall or recognition ofa stimulus list is enhanced ifa person must generate the list by using some rule (e.g., rhyming, synonym-antonym relations, multiplication) as opposed to simply reading the list. Theories describing this phenomenon include effort (see, e.g., Griffith, 1976; MeFarland, Frey, & Rhodes, 1980) or arousal (Jacoby, 1978); semantic activation (e.g., Graf, 1980;McElroy & Slamecka, 1982); relational processes (e.g., Donaldson & Bass, 1980;Rabinowitz & Craik, 1986); multiple-factor explanations (e.g., Hirshman & Bjork, 1988; McDaniel, Riegler, & Waddill, 1990;McDaniel, Waddill, & Einstein, 1988); and a procedural account (e.g., Crutcher & Healy, 1989;McNamara & Healy, 1995).To date, however, researchers have largely ignored the time-course of the generation effect. It is not clear whether the benefit from generation is derived from a continual strengthening ofmemory traces during the generation process as a whole, from a small number ofdiscrete changes during the course ofgeneration, or from a single discrete change in memory representation at the time when generation is completed. Slamecka and Fevreiski (1983) did study the related question of whether recall or recognition would be improved in the event of generation failures. They manipulated the difficulty ofan antonym generation and found that subsequent recall levels for stimuli that had been attempted but not fully generated were roughly as high as the levels for completely successful gen- -Accepted by previous editor, Geoffrey R. Loftus 135 erations, but that recall was much lower for stimuli that had only been read. Recognition tests showed intermediate levels of the generation effect for unsolved antonyms in this research. Slarnecka and Fevreiski interpreted these findings as evidence that generation in this task involved at least two processes: generation ofa semantic code and subsequent association of this code with a surface representation (an English word, in this case). According to this interpretation, the generation failures...