Emotion, information processing biases and inhibitory function

2.2.1.1 Anxiety

In her study on attention and anxiety. Fox (1994) argued that those tasks most likely to demonstrate an anxiety-related attentional bias towards threat material were also those most demanding o f selective attention, i.e. those which required effective inhibition o f distracting information. Fox presented evidence consistent with the view that anxiety sufferers are generally more distractible, and she relates the attentional bias towards threat to reduced inhibitory function. She writes:

“It is suggested ... that a deficit in the effective inhibition o f distracting information may be the causal mechanism which produces this preferential allocation o f resources to threat-related information in anxious individuals” (p. 191).

And goes on to say:

“...a defective inhibitory system in anxious individuals would explain why attentional biases are only apparent when there is competition for processing resources” (p. 192).

However, whilst this ‘defective inhibition hypothesis’ describes why the locus of mood-related processing deficits related to anxiety is attentional, the specificity o f this deficit (i.e. that resources are preferentially allocated to threat-related items) is not a natural consequence o f this hypothesis and must be presumed to be a function of present personal concerns in these patients.

2.2.1.2 Repressive coping and depression

Myers et a l (1998) explored inhibition within the context of suppressed recall, or cognitive avoidance, o f negative information in so called ‘repressive copers’. People

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possessing this cognitive style are identified as being those typically reporting low levels of distress on self-report measures but showing high levels o f distress (autonomic arousal) on physiological measures. Such cohorts have also shown impoverished recall of negative autobiographical and negative experimental material (Myers and Brewin, 1994; Myers and Brewin, 1995). In their study, Myers et al. (1998) demonstrated that repressive copers were more effective than normal controls at inhibiting the retrieval of negative information, compared to positive information, when instructed to do so. They interpret these results as providing evidence for a repressive coping style which results in the inhibited retrieval o f negative information, particularly that relating to the self. More recently. Power, Dalgleish, Claudio, Tata and Kentish (2000) demonstrated retrieval facilitation for to-be-forgotten negative words in clinically depressed subjects.

2.2.1.3 The role of inhibitory processes in information processing biases

It is unclear whether the role of inhibitory processes in information processing biases, as conceptualized by the above researchers, is a consequence of the mood disorder or plays a causal role in its development, and/or subsequent maintenance. Myers et al. are clearly o f the opinion that the heightened retrieval inhibition for negative self-related words in repressive copers reflects the functioning of an intentional coping style which has become automatized to some extent. Similarly, it might be the case that in the chronically anxious individual, the heightened levels o f distractibility Fox demonstrated, might reflect the operation o f something that started off as an intentional scanning of the environment for threat-related information (i.e. a deliberate distractibility), but which has become a well-leamed strategy which is now automatic.

However the work by Power et al. suggests the role o f inhibited retrieval in depression is less clear than for those involved in anxiety and repressive coping: sometimes cognitive avoidance and poor recall of negative material is demonstrated in depressed participants but often enhanced recall for such items is also shown. Whether cognitive avoidance/enhanced inhibitory function towards negative material reflects an

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individual difference (trait) variable or a more temporary shift in strategy by individual participants (state variable) is currently unclear.

In addition to empirical demonstrations o f the potentially important role of inhibition in chronic mood states noted above, inhibition has been invoked, at least implicitly, in theories o f cognition and emotion. The hypothesis that inhibition might play a crucial role in the continuation of emotional disorders is arguably hinted at by Teasdale and Barnard (1993) in their discussion of mood maintenance (see section 1.4.3), and it seems plausible that a failure to inhibit information processing may contribute to mood maintenance once a mild mood state has been established. In addition, Williams et al. (1997) argue that the recall bias towards negative information in depressives results from “the facilitated search for associated mnemonics at the elaboration phase” (Williams et a l, 1988; p. 175) whereas inhibition o f such nmemonic search will result in reduced recall or ‘cognitive avoidance’. It seems plausible to suggest that if enhanced specific inhibitory function relates to impoverished recall (as shown in ‘repressive copers’), decreased specific inhibitory function may relate to enhanced recall, such as that shown in chronic pain sufferers for pain-related words. In addition, the study o f inhibitory processes offers two further possibilities:

i) the potential to draw together work on poor overall task performance in chronic pain groups with the demonstration o f a pain-related recall bias, and,

ii) the possibility o f exploring whether retrieval or encoding processes seem principally responsible for the recall bias by exploring retrieval inhibition.

2.2.1.4 Inhibitory processes and pain

Gating, or inhibitory mechanisms, play a central role in the Gate Control Theory of Pain. These are conceived as operating throughout the central nervous system, including the brain. For example, in their discussion o f feelings o f tenderness which accompany injury, Melzack and Wall (1996) state:

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“Early evidence suggests that it (the feeling o f tenderness) does not simply fade away but is positively turned off by restorative control mechanisms” (p.

107).

Whilst physiological models are not necessarily relevant to cognitive models of pain, the role o f inhibition in cognitive processing in chronic pain patients has received scant attention. As noted earlier, inhibitory processes are considered crucial to efficient performance on a number o f different tasks and there is some evidence that performance on cognitive tasks is impaired in chronic pain sufferers. For example, chronic pain sufferers typically recall fewer words than control participants (e.g. Edwards et a l,

1992), have demonstrated slower reaction times in Stroop tasks (Pincus et a l, 1998), and taken longer to perform complex tasks when pain levels are high (Eccleston, 1995) than pain-ffee controls. Impaired task performance has been linked to reduced cognitive ‘resources’, although the exact reasons for reduced resources could be numerous and include the presence o f pain, reduced motivation and the result o f medication.

Inhibitory processes are linked by some researchers, although not all to the concept o f depleted cognitive ‘resources’. The term ‘resource’ is itself vague and has been used by different researchers to refer to different things. However, the aim o f the term is essentially the same as that of ‘attention’: i.e. to account for the limitation on the ability to do more than one thing/task at the same time. This limitation can arise because two tasks require the same structure, or because there is competition for a ‘central pool’ of cognitive resource or attention, unconstrained by specific structures. An example of the latter would be the Supervisory Attention System, proposed in the attentional model o f Norman and Shallice (1986). There has been a great deal o f criticism about the difficulties operationalizing (i.e. measuring) cognitive resources (e.g. Navon, 1984), a central problem being how to determine whether task perfoimance is deficient because too few resources are being deployed in the task (i.e. a motivational deficit exists) or whether cognitive resources are being used on task irrelevant processing (such as intrusive depressive thoughts, pain intensity) at the time o f task performance.

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Nevertheless, the issue does potentially have bearing on information processing biases in mood disorders (see section 2.2.3.3 and 2.2.3.4).

As noted earlier, the information processing biases in chronic pain sufferers demonstrated to date seem to be specific to explicit, effortful, recall tasks, notably free recall. Free recall is regarded as more resource demanding than recognition, cued recall and implicit retrieval and a link between information processing biases and reduced cognitive resources or cognitive efficiency is possible. In line with Williams et a/.’s (1997) conclusions about recall biases in depression, the pattern o f recall biases in chronic pain sufferers suggests that these biases are specific to controlled processes. Inhibitory processes have been discussed with reference to efficient performance and, in particular, have been linked to performance on controlled tasks.

The present study therefore aimed to explore the role of intentionally directed (retrieval) inhibition in recall biases o f pain sufferers by use o f the directed forgetting (DF) paradigm.