Working Memory and the Strategic Control of Attention in Older and Younger Adults

As proposed by Baddeley and Hitch (1974), working memory is a multicomponent, limited-capacity workspace capable of monitoring and transforming information while executing complex cognitive tasks. A crucial function of the working memory system is distinguishing between relevant and irrelevant information while maintaining task goals, often in the face of competing or distracting information (Engle, 1999). Because environmental demands are constantly changing, it is important that the contents of working memory be monitored and updated efficiently. Hasher and Zacks (1988) argue that older adults have deficits in attentional selection, thereby allowing more irrelevant information to enter working memory and occupy working memory resources requisite for efficient processing. Impaired selection can be a hindrance in everyday situations, for it is often necessary to attend to important information while directing attention away from less relevant information. This relates to the strategic control of attention, or the ability to optimally direct attentional resources and selectively encode high-value information (Castel, Balota, & McCabe, 2009). Given limited cognitive resources and an abundance of information in the environment, it is critical that individuals selectively attend to high priority or high-value information at the expense of low priority or low-value information. Consider, for example, wanting to remember the birthdays of loved ones. Although it is rare to remember the birthdays of every person one has known, being able to remember the birthdays of parents or grandchildren, for example, could be considered an efficient use of cognitive resources. Further, the capacity to inhibit irrelevant information is essential to using memory resources and attention in an efficient, goal-directed manner. It is often necessary to disregard certain information, for it may no longer be relevant to current task demands. Consider a change in dosage of medication. Alongside this change, it may be necessary to disregard previous instructions to take one pill every 4hr and now remember to take one pill twice a day. This requires forgetting of the previously relevant information along with maintenance of newly relevant information. To investigate age-related differences in the strategic control of attention, Castel and colleagues (2009) used a value-directed remembering task, wherein selective encoding was operationalized as encoding high-value stimuli in alignment with task goals. Participants were presented with a list of words, and each word was paired with a distinct point value ranging from +1 to +12. Participants were instructed to remember as many words as possible, with the goal being to selectively encode high-value words in order to maximize their total score. At the end of each word list, participants were provided feedback in the form of a summed score for words recalled. A selectivity index was later calculated for each participant by dividing their actual score by an ideal score based upon the number of words recalled (Castel, Benjamin, Craik, & Watkins, 2002). Across numerous variants of the value-directed remembering task, Castel and colleagues (2002, 2009) and Castel, Farb, and Craik (2007) found that older adults were equally as selective as younger adults when encoding high-value information, albeit at a cost of being able to recall fewer lower-value items. Castel and colleagues (2002, 2007) further claimed that older adults were exercising control in limiting attention to lower-value items while maintaining activation of the highest value items. Given that age differences are typically found on tasks requiring controlled processing (Park et al., 1996), the finding that older adults exercised control in maintaining selectivity is particularly surprising. In order to suggest that there are no age-related differences in the ability to strategically control attention, it is imperative that the task poses sufficient attentional demands to measure age-related differences in controlled processing. To increase task demands and investigate boundary conditions wherein age differences in selectivity may occur, the value-directed remembering task used by Castel and colleagues (2009) was modified in the current studies to include negatively valued items. Specifically, word lists were lengthened such that participants must limit the processing of negative-value words while selectively encoding high-value words. Point values were extended to range from −6 to +12. In this manner, the current studies most closely resemble Castel and colleagues (2007, Experiment 2), wherein 16 items were assigned point values ranging from −16 to +16, spaced in increments of four. Castel and colleagues (2007, Experiment 2) found that both age groups were able to maintain selectivity (with only two participants recalling negative-value words), although older adults displayed greater recognition of negative-value words. The inclusion of negative-value items bears semblance to directed forgetting tasks, such that negative-value words could be considered to-be-forgotten (TBF) items. Alternatively, positive-value words could be considered to-be-remembered (TBR) items. By including negative-value items, participants must now inhibit the processing of these items while maintaining activation of task-relevant (i.e., positive-value) items. Zacks, Radvansky, and Hasher (1996) found that older adults were more likely to recall TBF items, relative to younger adults, and this may reflect diminished efficiency of inhibitory control. This diminished efficiency may result in greater intrusion of task-irrelevant items, thereby cluttering the working memory space and limiting resources available for processing goal-relevant stimuli. It was predicted that younger adults would outperform older adults in the modified value-directed remembering task, and working memory capacity (WMC) was expected to support performance. Research suggests that individuals with greater WMC are better able to maintain activation of task-relevant information while inhibiting distracting interference, relative to individuals with lesser WMC, and a relationship between WMC and selectivity performance was expected (Kane & Engle, 2003; McCabe, Robertson, & Smith, 2005).