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Zacks, R. T., & Hasher, L. (1988). Capacity theory and the processing of inferences. In L. Light & D. Burke (Eds.), Language, Memory, and Aging (pp. 154-170). New York: Cambridge University Press. [Book reprinted in paperback, 1993]


Excerpt from the Chapter: The study of adults age differences in comprehension of and memory for text is an now burgeoning enterprise in cognitive gerontology, in part because of the potential for direct application to the findings to everyday life. To date, the work on discourse processing suggests the existence of age deficits of varying magnitudes, deficits that are largely quantitative rather than qualitative in nature. The work thus suggests that older adults use the same processing mechanisms as younger adults but with poorer results (e.g. Mandel & Johnson, 1984; Zelinski, Light, Gilewski, 1984).

Beyond this summary the literature yields few simple generalizations: indeed, the findings on any given variable (e.g., education level) tend to be complex and inconsistent. Consider the literature on the recall of ideas that differ in their importance to the meaning structure of the text. The usual finding with young adults (called the "levels effect") is that the probability of recalling information from text is directly related to the information's importance level in the text as defined by a model (e.g., Kintsch's, 1974) of the hierarchical structure of that text. When young and elderly adults have been compared, different experiments have produced contradictory results. . . The most frequent findings are (1) parallel levels effects for younger and older adults (e.g., Zelinski et al., 1984); or (2) an exaggerated levels effect for the older adults, with the greatest age deficit seen at low importance levels (e.g. Dixon, Hultsch, Simon, & von Eye, 1984, for high verbal ability subjects; Spilich, 1983). However, there is also an occasional finding of a diminished levels effect for older adults with the greatest age deficit at high importance levels (e.g., Dix et al., 1984, for low verbal ability subjects).

Conflicting results of this sort suggest the likelihood that additional variables are operating. In the case of the levels effect, such variables as education, verbal ability, and characteristics of the experimental texts (e.g., the familiarity of the text structure and/or its content) might mediate the variable aging trends (Dixon et al., 1984, Meyer& Rice, 1981). The suggestion that such variable interact with age differences is consistent with Jenkin's (1979) tetrahedral model of memory which argues that memory performance in a particular situation is a joint function of the characteristics of the subjects, of the materials they are required to remember, of the acquisition conditions, and of the critical tasks.

We are sympathetic with the general goals of identifying and classifying the multiple factors that control age difference in memory for text. However, we believe that the pursuit of these goals will benefit from theoretical analyses which indicated the specific characteristics of subjects, materials, and tasks that might be functional in a particular situation. Thus, we chose a different approach to the general problems of age differences in discourse comprehension and memory.

The theoretical orientation guiding our research on discourse processing derives from limited-capacity attention theory (Kahneman, 1973). We began our research program with a general limited-capacity framework which made few specific claims about either the nature of capacity constraints on text processing or age differences. The initial framework and its associated research led us to elaborate on our capacity model in such a way as to increase the precision of our analysis of age differences in discourse processing. In this paper we trace the development of our thinking by reporting a line of research that at first seemed to support and then to constrain the value of our initial general-capacity model. We also outline our elaborated view on which future research will be based.

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