Psychology and Aging 1998, Vol. 13, No. 2, 256-266 Copyright 1998 by the American Psychological Association, Inc. 0882-7974/98/S3.00 Adult Age Differences in the Temporal Characteristics of Category Free Recall Arthur Wingfield, Kimberly C. Lindfield, and Michael J. Kahana Brandeis University Two experiments are reported that examined the temporal structure of recall for categorizable word lists by younger and older adults. All participants showed response bursting, in which recall order is clustered by semantic category, with longer interresponse times (IRTs) appearing between catego- ries than within categories. Experiment 1 demonstrated that older adults, even when matched to younger adults in overall accuracy, differed in the rate of increase of between-category IRTs with output position, but not in within-category IRTs. Experiment 2 showed that this interaction is elimi- nated when the names of the response categories are provided to the participants. Results are interpreted in terms of combined effects of an age-compromised episodic memory system (between- category IRTs) accompanied by a comparatively preserved semantic system (within-category IRTs) in healthy aging. Since the pioneering work of TUlving (Tulving & Pearlstone, 1966; Tulving & Psotka, 1971), it has been generally accepted that retrieval failure is the dominant cause of forgetting in stud- ies of verbal learning and memory. It thus follows that to under- stand forgetting we must understand the mechanisms of retrieval. What are the relevant retrieval cues, and how does the remem- berer use them under varying circumstances? In some memory tasks, such as recognition memory, fragment completion, and cued recall, retrieval cues are directly available. In free recall, however, the individual must initiate the formation of the re- trieval cues that may facilitate access to the desired information. After some years of neglect, the cognitive literature has shown a resurgence of interest in the retrieval dynamics of free recall from episodic memory (Kahana, 1996; Kahana & Loftus, in press; Rohrer, Wixted, Salmon, & Butters, 1995; Wixted & Rohrer, 1996). The focus of these studies on episodic memory honors Tulving's (1972, 1983) distinction between episodic memory (memory for events, to include stimuli such as word lists learned in an experiment) and semantic memory (general knowledge not tied to a specific context). The temporal output pattern observed in the free recall of verbal items such as digits or word lists is characterized by a Arthur Wingfield, Kimberly C. Lindfield, and Michael J. Kahana, Department of Psychology and Volen National Center for Complex Sys- tems, Brandeis University. We acknowledge support from National Institute on Aging Grants R37 AG15852 and T32 AG00204 and National Institute of Mental Health Grant R29 MH55687. We also acknowledge support from the W. M. Keck Foundation. We thank Kelly Sullivan for help in running the participants in Experi- ment 2 and Anthony J. Velez for help with the latency measurements and technical support. Correspondence concerning this article should be addressed to Arthur Wingfield, Volen National Center for Complex Systems, MS 013, Bran- deis University, Waltham, Massachusetts 02254-9110. Electronic mail may be sent to wingfield@volen.brandeis.edu. phenomenon known as response bursting (Bousfield, Cohen, & Whitmarsh, 1958; Bousfield & Puff, 1964; Bousfield & Sedge- wick, 1944; Bousfield, Sedgewick, & Cohen, 1954). A clear case of this effect was described by Pollio, Richards, and Lucas (1969) who had participants learn lists of randomly arranged words drawn from several semantic categories. Under these con- ditions, participants tend to recall words clustered by category, with short interresponse times (IRTs) between items recalled from within a category and longer IRTs at the transitions between categories (Pollio, 1974; Pollio et al., 1969). Although IRTs generally increase exponentially as recall proceeds, Pollio et al. found that for categorized lists the increase in between-category IRTs was much larger than the increase in within-category IRTs. This increase in between-category IRTs, however, is eliminated when the names of the categories used in the study list are provided to participants either at the start of the study trials or at the time of recall (Patterson, Meltzer, & Mandler, 1971; Pollio & Gerow, 1968). Patterson et al. (1971) postulated that between-category IRTs reflect the combined effects of the time needed to determine that no more items from a category can be recalled (category exit time) plus the time needed to gain access to the next cate- gory (category-access time). Once accessed, the participant may then use the category-retrieval cue to obtain the first word in the new category (word access). This characterization of IRTs is consistent with the view that in list learning, the learner spontaneously organizes the list into higher order units and then uses these higher order units to cue the recall of the individual words (Tulving, 1968; Wingfield & Byrnes, 1981, pp. 80-86). In this regard, Tulving and colleagues (Tulving & Madigan, 1970; Tulving & Pearlstone, 1966) have drawn an important distinction between cue-dependent forgetting and trace-depen- dent forgetting. Cue-dependent forgetting refers to the failure to retrieve a higher order unit such as a category name that can serve as a retrieval cue. Trace-dependent forgetting refers to the failure to retrieve an elementary unit such as an individual word belonging to a given category. In the free recall of categorizable 256