The discussion in Chapter 1 and the foregoing subsection established that the item and list method directed forgetting paradigms represent a means for fostering a task environment that will be sensitive to age-related differences in attentional inhibition. Nonetheless, as discussed earlier, an additional mechanism has been proposed to account for the item method directed forgetting effect:
Basden et al., 1993), Accordingly, if it is assumed that the item method directed forgetting effect is mediated by differential rehearsal at encoding, evidence o f an age-related decline in the magnitude o f the item method directed forgetting effect would be consistent with the notion that ageing is associated with a deficiency in elaborative processing. However, as discussed earlier, the ability o f older adults to adopt a differential rehearsal strategy is also determined by the selective inhibition o f the rehearsal o f F cued items, which is likely to be particularly demanding because o f the item-by- item change in retrieval instruction (Zacks et al., 1996).
One potential approach to disentangling the contributions o f retrieval inhibition and differential rehearsal is to vary the amount and type o f item-specific, differential rehearsal conferred on R and F items. This can be achieved by varying the type and temporal location o f rehearsal opportunities. Indeed, such manipulations have been shown to have a differential effect on the retrieval o f R and F cued items (e.g., Hauselt, 1998; see also. Chapters 1, 7, & 8). For example, Gardiner et al. (1994) demonstrated that F and R cued items can be held in abeyance at encoding until the directed forgetting cue is provided, before undergoing differential rehearsal. In particular, varying the interval between the critical item and the onset o f the cue allows the systematic variation in the length o f time R and F items undergo maintenance rehearsal; and following cue onset, critical items undergo elaborative rehearsal, in accordance with the cue designation (Bjork, 1972). Therefore, this particular manipulation was utilised with the category exemplar generation task in order to try and disentangle the contribution o f differential rehearsal and inhibition to the item method directed forgetting effect (Experiment 3).
3.2.4 Attention and Memory: Evidence from Divided Attention
The concept o f attention as a processing resource that changes with age, and so determines the way in which certain cognitive processes operate has been espoused by several authors (Craik & Byrd, 1982; Hasher & Zacks, 1979; Plude & Hoyer, 1985). Central to several theoretical accounts o f cognitive ageing is the assumption that conscious, recollective m em ory processes are dependent on attention at encoding, whereas unconscious memory processes are only minimally dependent on attention at encoding (Bentin, 1994; Besson, Fischler, Boaz, & Raney, 1992a; Jacoby et al., 1993b; Jacoby et al., 1989; Parkin & Russo, 1990; Shallice et al., 1994; Szymanski & M acLeod, 1996). This view is also consistent with the more general notion that only controlled or effortful, rather than automatic, processes are dependent on the allocation o f attention (Hasher & Zacks, 1979;
referred to as the attentional view.
3. Conscious and Unconscious M emory Processes and Ageing
The notion proposed by Jacoby and colleagues (Jacoby, 1991; Jacoby et al., 1989; Jennings & Jacoby, 1993) that ageing only impairs consciously controlled processes appears to conflate attentional control with attentional resources, thereby limiting the ability to interpret instances when resource demanding processes, such as self-initiated retrieval, operate automatically (Craik et al.,
1996). Under such conditions, the cognitive effort expended is observed as impaired performance on the secondary task, rather than in impaired memory task performance (Craik et al., 1996; cf. Fem ades & Moscovitch, 2000). However, the difficulty with distinguishing between resource demands and cognitive control is that it is not easily accommodated by single-resource theories o f attention, and for other reasons that are outside the scope this discussion, the notion o f a global pool o f processing resources has been the subject o f much debate (Hirst & Kalmar, 1987).
The attentional view has also been articulated in terms o f a neuropsychological model. In particular, M oscovitch and colleagues proposed a neuropsychological, component-process model in which two components, an associative, automatic modular component and an intentional strategic (‘frontal’) component, interact to determine encoding and retrieval in direct memory tests (Femades & M oscovitch, 2000; M oscovitch, 1994a; Moscovitch & Winocur, 1995). The strategic component operates to direct attention to the information that represents the input to the modular system. Dividing attention at encoding decreases the likelihood that information will be encoded adequately by the m odular system, leading to impaired memory (Bentin, M oscovitch, & Nirhod, 1998), because o f the localised effect on the strategic component (Moscovitch, 1994a). Clearly, when this model is framed in terms o f the ‘frontal lobe deficit’ account o f ageing (West, 1996), a disproportionate impairment in older adults under conditions o f divided attention would be predicted (M oscovitch & Winocur, 1995).
The second approach that can be adopted for interpreting the effects o f divided attention at encoding on memory retrieval is the transfer appropriate processing view. According to this framework, divided attention at study is expected to reduce the amount o f conceptually based processing, but have little or no effect on perceptual processing (Broadbent, 1971; Craik, 1983; M ulligan, 1998). Therefore, the effect o f divided attention at encoding should only be observed with conceptual direct and indirect memory tests, and not perceptual direct and indirect memory tests (Mulligan, 1998). Combining this distinction between perceptual and conceptual processing
requirements for encoding o f semantic information. There is evidence for automatic semantic activation during the course o f word identification (Carr, 1992; Neely, 1991), but word identification is also attention demanding because it involves the elaboration and integration o f words within a spatiotemporal context (Bentin, 1994). In contrast, the context-invariant features o f words are longer lasting and are encoded automatically (Bentin, 1994). The conceptual encoding involved in category exemplar generation is primarily mediated by context-dependent, rather than core, semantic features because less typical category exemplars are normally selected for use in this memory task. Clearly, there is a need for experimental work investigating the effect o f divided attention on conceptual conscious and unconscious processes in order to provide a better understanding o f the role o f attention at encoding for subsequent mem ory retrieval, when the effect o f contamination by conscious retrieval has been excluded.
Other explanatory frameworks such as the response bottleneck view have been proposed (Pashler, 1994), however these appear to able to account for only a subset o f the divided attention and memory data. Briefly, processing bottlenecks are hypothesised to arise because some operations are mediated by a single mechanism that cannot be shared between two tasks. Thus, a switching strategy is necessary under these conditions, rather than the sharing o f a mechanism, as would be the case in the attentional resource capacity model. However, the limited amount o f data investigating this conceptualisation as a means for interpreting age-related differences in dual-task performance precludes an examination o f its explanatory power. Further, given the serial nature o f the divided attention task that was employed in the experimental work presented in the thesis, this model cannot be directly evaluated. Thus, the studies to be reported were conceived and planned to address the sometimes competing predictions o f the attentional view and the transfer appropriate view; accordingly, the following subsection is described prim arily in terms o f these two views.