Memory

Memory stage theory separates memory into the temporal, sequential components that define any act of remembering. Information first has to be perceived or experienced (i.e., encoding). Then the information has to be maintained over a retention interval of some length of time (i.e., storage). Finally, the information has to be produced at the time memory is tested (i.e., retrieval). Early researchers believed that adult age differences in memory were located primarily at retrieval, the final of the three stages. Early laboratory research, for example, demonstrated that age differences were large when the recall of a word list was measured (with instructions such as "Write down all the words you can remember having seen on the list presented earlier."). Age differences, however, were greatly reduced or even eliminated when recognition memory was used to test memory at retrieval (with instructions such as "Select the words on this list that were presented on the list that you saw earlier."). Because the use of a recognition memory task is assumed to reduce the retrieval requirement of the memory task, it was then inferred that the locus of the age effect must be retrieval. Such findings were prevalent in the 1960s and 1970s.

More recent research, however, has clearly demonstrated that recognition memory is not totally insensitive to aging, and the stage theory lost its appeal because of the methodological difficulties in isolating one memory stage from another in different age groups. In order to isolate retrieval, for example, everything must be held constant until the time retrieval is tested. This is Figure 1 Age group differences in working memory (as measured by computation span), episodic memory (as measured by free recall), and semantic memory (as measured by vocabulary). SOURCE: Adapted from Park, Lautenschlager, et al. in press. Copyright © 2002 by the American Psychological Association. Adapted with permission. difficult to accomplish in aging research, however, because adults of different ages may process information differently at one of the earlier stages, thus violating the requirement that all be held constant until retrieval (Smith).

The major reason, however, for the loss of interest in identifying the stage at which aging had its effects is clear evidence that age has effects on all stages of memory: encoding, storage, and retrieval. For reasons not directly related to memory stage theory, however, memory research in the 1970s and early 1980s focused heavily on the encoding stage of memory. This focus on encoding was due to the development of a conceptual view of memory, the "levels of processing" framework, which proposed that the ability to remember was determined by the extent of semantic processing during the encoding of the to-be-remembered information (Craik and Lockhart). For this reason, much research on memory and aging during this period focused on the nature of encoding processes in different age groups. Even with the magnitude of the research effort, however, the relationship between aging and levels of processing is still unclear. The research did, however, suggest that encoding is especially affected by adult aging. For example, the memory performance of older adults, relative to younger adults, is more detrimentally affected by performing a divided attention task during the encoding stage of a memory task, but not if the divided attention task occurs at retrieval (Park, Smith, et al.).