Aging is characterized by declines in a large number of aspects of the cognitive system (e.g. Salthouse, 1991; Kausler, 1994). An important question is whether the number of mechanisms behind these declines is smaller than the number of processes involved. The present application operates within the levels-of-dissociation framework, formulated by Kliegl and associates (e.g. Kliegl, 1996; Verhaeghen, Kliegl, & Mayr, 1997), which states that age-related differences in speed and accuracy are characterized by certain well-defined, discrete transitions between different levels of processing complexity. More specifically, the investigator intends to investigate the distinction between sequential processing (i.e., processing that is carried out in a number of independent processing steps) and coordinative processing (i.e. processing while a need exists for organizing the transfer of information between processing steps, thus forcing the system to store intermediate results in working memory while concurrent processing is going on). Currently, a number of crucial assumptions and implications of the framework have gone uninvestigated. The present application is aimed at remediating this situation. (1) Higher-order regularities in the sequential-coordinative distinction will be investigated. Are the effects truly modular, as Kliegl (1995) has proposed; or should they rather be conceptualized as state transitions? (2) The proposed all-or-none character of the jump from sequential to coordinative processing in late adulthood will be examined. Do substantial increases in working memory load indeed not lead to further dissociations? (3) The coordination assumption will be tested. Is coordination - stacking information into working memory and retrieving it while concurrent processing is going on - truly the crucial factor, or is a passive working memory load hypothesis sufficient explanation? (4) It will be tested whether the mode of processing changes from sequential to coordinative processing, and whether an age differential exists in such mode shifts. (5) Finally, it will be tested whether an artifact/disuse interpretation of the distinction is feasible, or whether the dissociation persists after a period of extended practice.
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