Rabasa Gamboa, Emilio “Las reformas constitucionales en Materia Político-

Inhibition is one o f the primary constructs that has been applied to interpret age-related differences in the ability to retrieve information from memory (Hasher, Stolzfus, Zacks, & Rypma, 1991; Hasher & Zacks, 1988; Zacks & Hasher, 1994). Hasher and Zacks (1988) proposed an influential framework in which inhibition was characterised in terms o f its operation within selective attention; selective attention was argued to be supported by activation and inhibition processes. Typically, activation processes are characterised as largely unconstrained as compared to the intentional, controlled nature o f inhibitory processes (Hasher & Zacks, 1988; Houghton & Tipper, 1996). Further, attentional inhibitory based processes are argued to allow selection among response alternatives (Arbuthnott, 1995). Inhibition has also been characterised as a more theoretically neutral construct, which is not deterministic (Anderson & Bjork, 1994). The primary locus o f age deficits in cognition are assumed to be within attentional inhibitory processes (Hasher & Zacks, 1988). However, the precise nature o f the attentional inhibition mechanism, as it relates to the identification and suppression o f items, has not been specified with sufficient precision (Arbuthnott,

1995).

In terms o f the framework proposed by Hasher and colleagues, inhibition is argued to suppress the activation o f irrelevant, or selected-against, information that can potentially enter working memory,

attention on previously rejected information (Hasher & Zacks, 1988; May, Kane, & Hasher, 1995). One prediction arising from this view is that there should be reduction in the capacity o f working memory, resulting from the inability to sufficiently suppress irrelevant forms o f processing (Engle, 1996; Stoltzfus, Hasher, & Zacks, 1996), which will, in turn, have a larger effect in older adults because o f the diminished attentional capacity associated with ageing. In addition, these effects are argued to lead to increased processing time and reductions in the conscious retrieval o f relevant information (Hasher & Zacks, 1988).

Several different sources o f experimental work are consistent with the attentional inhibition framework proposed by Hasher and Zacks (1988). These include a wide variety o f complex tasks that involve language comprehension, speech production, and working memory. For example, negative priming and susceptibility to interference from distracting text when reading are both impaired in older adults relative to young adults (e.g., Kane, Hasher, Stolzfus, Zacks, & Connelly, 1994; for a review, see McDowd & Birren, 1990). However, Kramer and Larish (1996) failed to find age-related impairment in tasks such as negative priming, the W isconsin Card Sorting Test (WCST), and the stopping paradigm (Logan, 1994). Nonetheless, Kramer and Larish (1996) did report an impairment in stopping an overt response and adopting new rules in a categorisation task. Kramer and Larish (1996) argued that the selective pattern o f age deficits suggests that inhibitory processing does not undergo a diffuse decline in older adults; rather, the nature o f the decline is better characterised in terms o f selective deficits within a subset o f inhibitory processes (see also, Arbuthnott, 1995; Arbuthnott & Campbell, in press; Dempster, 1992).

In contrast to the conceptualisation o f inhibitory processes proposed by Hasher and Zacks (1988), Jacoby and his colleagues have characterised ageing in terms o f a loss o f conscious control, accompanied by a preservation o f unconscious, automatic processing (Hay & Jacoby, 1996; Jennings & Jacoby, 1997). W ithin this account, the deficit in consciously controlled processes is assumed to reflect a primary impairment in executive control, as conceptualised within the central executive component o f working memory (Baddeley & Hitch, 1974); whereas. Hasher and Zacks (1988) proposed that the deficit in executive control was a secondary consequence o f a decline in inhibitory processes. The impairment in executive control is assumed to be expressed by an increased role for automatic, unconscious processes in older adults. In the following experimental chapters, both the inhibitory deficit and loss o f conscious control accounts will be discussed in a variety o f different experimental contexts.

3. Conscious and Unconscious M emory Processes and Ageing

3.2.2.1 Ageing and Inhibition: Evidence from List and Item Method Directed Forgetting

The current section addresses the role o f inhibitory processes that are assumed to operate within the item and list method directed forgetting paradigms. Only a limited amount o f experimental work has been conducted to investigate the nature o f the inhibitory mechanisms in directed forgetting as a function o f age (see Chapters 7 and 8). The emerging research examining the effect o f designating an item at study as either to-be-remembered (R) or to-be forgotten (F) has been the subject o f a number o f reviews (Bjork, 1972; Bjork, 1989; Epstein, 1972; Johnston, 1994; M acLeod, 1998). As discussed in Chapter 1, several interpretations o f the list method directed forgetting effect have been proposed, however the predominant mechanism is retrieval based inhibition (Basden & Basden, 1996; Basden & Basden, 1998; Basden et al., 1993). In addition, inhibitory based processes have also been implicated in the item method directed forgetting effect, however these are argued to operate to terminate the rehearsal o f F cued items (Zacks & Hasher, 1994; Zacks et al., 1996). Two studies presented in this thesis investigated the relationship between behavioural intentions and inhibition in terms o f the ability to operate according to the list method paradigm (Experiments 4 & 6).

The theoretical motivation for applying the item and list method paradigm was the ability o f these paradigms to invoke inhibitory based processing. Accordingly, the experimental work conducted was designed to extend the understanding o f age-related differences in inhibitory processes to directed forgetting associated with conscious and unconscious processes, as defined within category exemplar generation and perceptual-associative word stem completion mem ory tasks. In particular, utilising the item and list method directed forgetting paradigm enabled the evaluation o f two assumptions within framework posited by Hasher and Zacks (1988): (1) inhibition serves to suppress no longer relevant information; and (2) inhibitory processing is impaired in older adults. A decline in the magnitude o f the list-method directed forgetting effect in older adults would be consistent with the original proposal by Hasher and Zacks (1988) relating to these two assumptions.

More specifically, older adults may be less able to accurately encode and retrieve the R or F cue designation associated with each item, because o f the generalised slowing associated with ageing and lapses in registering the cue designation (Zacks et al., 1996). However, the attentional demands that are likely to lead to such conditions may be more acute in the item method paradigm, but the difficulty with attributing an age-related deficit in the m agnitude o f the item method directed

differential rehearsal o f R and F cued items. Therefore, it is necessary to disentangle the contribution o f inhibition and differential rehearsal based processes to the item method directed forgetting effect (cf. Zacks et al., 1996). This issue will be expanded in the Chapters 7 and 8. Similarly, an attenuated list method directed forgetting effect in older adults can also be attributed, in part, to age deficits in memory for spatiotemporal contextual information (Craik & Jennings, 1992; Spencer & Raz, 1995), since it cannot simply be assumed that strategic differences do not exist between young and older adults in the manner in which the task is performed (for additional discussion o f this issue, see Chapters 7 & 8). Further, m emory for spatiotemporal contextual information is potentially a particularly significant mediating factor at longer study and test intervals, because the effort required to inhibit the rehearsal o f F items will increase as a function o f time (Zacks et al., 1996).

In summary, to the extent that the list method (and to a lesser extent the item method) directed forgetting effect is mediated by the inhibition o f the F items, older adults would be expected to be less able to comply with the instructions associated with F cues, since as discussed, a variety o f paradigms that invoke intentional inhibitory processes have provided evidence o f a decline in older adults (for a review o f such paradigms, see Zacks & Hasher, 1994). However, the magnitude o f the effects that indicate impaired inhibitory processes, although significant, have been relatively small (Hamm & Hasher, 1992; Hartman & Hasher, 1991; Zacks et al., 1996), and it may be that these age effects are contingent, in part, on the nature o f the inhibitory processes that are being invoked (Kramer, Humphrey, Larish, Logan, & Strayer, 1994).