An intuitive analysis reveals that different ProM activities are associated with different conscious experiences. For example, waiting for the pot to boil is a short-term task; it is likely to be kept active in working memory and to dominate conscious awareness. By contrast, if we plan in the morning to get groceries en route from work later in the day, this involves a different type of conscious experience. This plan is not likely to remain active and dominant in working memory; it is out of conscious awareness for most of the retention interval (i.e., the period between making the plan and executing it). Instead, the retention interval is filled with other activities, the ProM-task-relevant cue (e.g., the supermarket) appears incidentally as a natural part of these other activities (e.g., driving home from work), and what is of interest is whether the cue succeeds in bringing the previously formed plan back into conscious awareness (Einstein & McDaniel, 1996; Graf & Uttl, 2001; Kvavilashvili, 1998; Mantyla, 1996; Meier & Graf, 2000).
The different conscious experiences associated with these different prospective activities seem analogous to the experiences that characterize performance on primary- and secondary-memory tasks, and thus it seems reasonable to proceed in the spirit of William James's work. James stipu lated that "memory proper'' requires "the knowledge of an event, or fact, of which meanwhile we have not been thinking, with the additional consciousness that we have thought or experienced it before'' (1890, p. 684). By analogy, we propose to define ProM proper as requiring that we are aware of a plan, of which meanwhile we have not been thinking, with the additional consciousness that we remember making the plan earlier. By this definition, ProM proper does not encompass the prospective equivalent of primary memory, that is, when a plan or intention remains active in working memory throughout the retention interval. The latter situation is more typical of vigilance or monitoring tasks, and thus such labels seem more appropriate for the ProM equivalent of primary memory (cf. Baddeley & Wilkins, 1984; Craik & Kerr, 1996; Einstein & McDaniel, 1996; Meacham & Leiman, 1982).2
We regard vigilance and ProM proper as part of a continuum of possible prospective-memory activities. At one end of this continuum, the prospective task dominates working memory and conscious awareness during the retention interval. At the other end, the ProM-proper end, the plan is out of working memory during the retention interval and conscious awareness is focused on competing activities. We hypothesize that what varies along the continuum is the proportion of available processing resources allocated to the prospective task during the retention interval. For vigilance, all or most of the available resources are allocated to the prospective task, whereas for ProM proper, all or most of the available resources are allocated to competing activities. Other tasks, such as waiting for the arrival of a limousine or for the cupcakes to finish baking may fall between these extremes (see Ceci & Bronfenbrenner, 1985; Dobbs & Reeves, 1996; Harris & Wilkins, 1982). Such tasks may recruit a more equal allocation of resources to prospective and other activities.
The domain of ProM proper seems further circumscribed by the distinction between episodic and habitual tasks (Harris, 1983; Meacham, 1982), which appears analogous to the distinction between episodic and semantic memory tasks. Buying groceries en route from work is an episodic task, like an episodic-memory task, in the sense that the plan arose out of a single event and is to be executed only once. By contrast, taking medication and brushing one's teeth at bedtime are habitual tasks; they are similar to semantic-memory activities that have been shaped by many previous repetitions. Episodic and habitual tasks are radically different from each other: they arise out of different needs, they are associated with different conscious experiences, and they are marked by different histories (i.e., number of occasions for thinking about and practicing them). For these reasons, by analogy with Tulving's (1972) distinction between episodic and semantic memory, we use the label ProM proper only in reference to episodic or one-off tasks.
Our focus in this chapter is on ProM proper, specifically, on responding to cues as telltale signs of previously formed intentions. ProM proper seems to be the direct complement of explicit episodic RetM. For this reason, an investigation of ProM proper is most relevant to theoretical assumptions about age-related changes in prospective and retrospective memory (see Craik, 1986).
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