Aging and the distribution of resources in working memory

While limitations in human information processing capacity have long been acknowledged, the conceptualization of these limitations in experimental psychology has evolved from that of a passive storage system to one of an activated subset of an extended knowledge net; rather than a unitary system, this working memory is thought of as a group of distributed capacities or modules, both dynamic and flexible in their operation. The focus of the present chapter has been on age differences in how resources are distributed within this working memory system, particularly in the course of language comprehension. Brinley analyses of reading times do not appear to conform to the patterns observed in response times for correct responses in discrete-trial tasks, e.g., lexical decision, mental rotation. While similar to discrete-trial data in showing an orderly relationship between the latencies of younger and older adults, the slope of the resulting functions appear to be routinely close to unity rather than to the 1.5 typically found in discrete-trials tasks in which time is measured for successful performance. Unlike those of discrete-trial tasks, the Brinley plots of reading time are not directly relevant to the Slowing Hypothesis. Rather, because any individual reading time does not necessarily correspond to a unit of successfully completed processing (e.g., orthographic decoding, lexical access, contextual instantiation, intraconstituent organization, interconstituent integration, integration with world knowledge, etc.), Brinley plots of reading times reflect the relative allocation of processing resources by young and old as text demands increase. The slope of unity suggests a large measure of similarity between resource allocation strategies of younger and older readers. Subsequent memory and comprehension performance, however, often reveal age differences favoring the young, suggesting that age constancy in reading strategy may not be adaptive. The Brinley approach was augmented by the use of regression analyses of reading time in which specific cognitive constructs underlying the reading times could be identified. These analyses substantially supported the Brinley analysis in showing great similarity between how younger and older readers responded to specific text demands, but also suggested that older adults were allocating somewhat less time to developing a cognitive representation of the text-based meaning of the discourse. Older adults who showed high levels of memory performance were those who used a more top-down approach, thus implicating the importance of developing new styles of resource distribution to accommodate processing declines.