Are these cognitive distortions related to environmental stimuli and do these distortions have an impact on emotion and behaviour

This question is equally important because the cognitive model specifies that negative thoughts will not occur randomly, but in response to specific events that are misinterpreted by the individual. Moreover, this misinterpretation is said to fuel a cycle of negative emotions, and influence the behaviour of the depressed individual. Phrased in more technical terms, these ideas have been termed selective processing and primacy. The selective-processing hypothesis states that depression is characterized by a processing bias for negative self-referent information from the environment. The primacy hypothesis posits that negative cognition influences both behaviour and emotion (Clark et al., 1999; Haaga et al., 1991).

It is important to note that the cognitive theory of depression does not suggest that depressed persons are always biased in their information processing (Segal, 1988). Rather such biases are most likely to emerge in situations that are personally relevant, and that offer a degree of ambiguity (Beck, 1967; Clark et al., 1999). Unlike the research on negativity and specificity, which often involves simple self-report, evaluation of the selective-processing hypothesis involves more laboratory-based studies. Participants in such studies are placed in a variety of specifically constructed situations, ranging from imagined scenarios in which an outcome is predicted, to performing a task and receiving feedback from others. Indeed, these studies do suggest that depressed individuals find negative and positive interpretations of ambiguous stimuli equally acceptable, whereas non-depressed individuals prefer positive interpretations (Crowson & Cromwell, 1995, Moretti et al., 1996). Depressed individuals are more likely to perceive their own performance of an experimental task as less positive and more negative (e.g., Dykman et al., 1989; Weary & Williams, 1990), though some studies have suggested that depressed individuals see their performance as less positive only (DeMonbreun & Craighead, 1977). Similarly, depressed individuals judge their social performances to be more negative than do non-depressed individuals (Dow & Craighead, 1987; Gotlib & Meltzer, 1987). Depressed individuals selectively recall more negative self-referent adjectives in memory-based tasks, although in some studies depressed individuals recall fewer positive adjectives and not necessarily more negative adjectives (e.g., Kuiper & Derry, 1982). Moreover, the responses of depressed individuals to standardized, open-ended vignettes of typical achievement and interpersonal experiences often contain negative distortions (Krantz & Hammen, 1979; Krantz & Liu, 1987; Watkins & Rush, 1983), especially when the vignette is itself negative (Krantz & Gallagher-Thompson, 1990). This is true whether the comparison group comprises non-distressed controls or mixed psychiatric controls (Haaga et al., 1991). Similarly, an examination of the thought records of depressed patients in treatment has revealed cognitive errors in response to situations that patients had recorded themselves (Blackburn & Eunson, 1989). Moreover, whether responses are gathered in the context of a laboratory or in the clinic, the types of cognitive errors made by depressed individuals appear to be similar. Arbitrary inference (for example, attributing a cause in the absence of evidence), magnification (such as making a small mistake and seeing this out of all proportion), overgeneralization (as in taking a single case and seeing that as a general, negative rule), and personalization (such as attributing a negative outcome to the self) are the most common cognitive errors reported in these studies (Clark et al., 1999). Such studies certainly support the notion of selective, negative processing of information in depression.

However, there are also several issues in the area of selective processing that have been controversial. In some studies of information processing, depressed individuals have actually been found to be more accurate than those of non-depressed individuals. This effect has been termed "depressive realism" or the "sadder but wiser" phenomenon (Abramson & Alloy, 1981). Obviously, if the perceptions of depressed people are sometimes more accurate than those of non-depressed people, the notion of selective processing and the cognitive model itself are open to challenge. However, closer examination of the experimental findings has suggested that there are specific conditions under which depressed individuals are more accurate, and that the depressive realism notion does not hold uniformly (Clark et al., 1999). Specifically, it seems that depressed people may be more accurate when asked to judge the probability of abstract outcomes, but not when judging personally relevant, everyday situations, which are much more central in the experience of depression (Clark et al., 1999; Haaga & Beck, 1995). Another issue, and one that remains unresolved despite its prominence in the cognitive model, is the empirical status of the cognitive distortions. Depending on which source reference is used, the cognitive model sets out variable numbers and types of cognitive distortions. It has been relatively straightforward to demonstrate that depressed individuals have biases that are negative in tone. It has been more difficult to construct a comprehensive empirical taxonomy of the kinds of distortions depressed individuals make.

The next hypothesis to be explored in this section, that of primacy, predicts that there is a link between negative distortions and the individual's emotions and behaviour. One programme of research has illustrated that ruminative, self-focused negative thoughts are systematically related to enduring negative mood, particularly among depressed women (Nolen-Hoeksema, 1991; Nolen-Hoeksema et al., 1993). Other studies attempt to reduce negative thought content to examine the impact of such cognitive change on affect (Persons & Burns, 1985; Teasdale & Fennell, 1982). Overall, both types of studies demonstrate a reciprocal link between negative moods and negative thoughts. There is also evidence that negative cognition is associated with both peripheral physiological changes and changes in cortical activity. Negative cognition has been linked to increased heart rate (Schwartz et al., 1981) and respiration rate (Schuele & Wiesenfeld, 1983), as well as to cerebral blood flow through the limbic, paralimbic, and brainstem structures in positron emission tomography (PET) studies (George et al., 1995). The difficulty with such physiological studies is teasing apart the nature of relationships between cognition and emotion. The design of these studies has typically been correlational rather than experimental, and the degrees of association are sometimes modest. For better establishment of causality, some studies induce a negative mood and then examine the impact of the mood on cognitive networks, and these studies also support the primacy hypothesis (Ingram et al., 1998).

Unfortunately, less research is available on the connection between depressive thinking, mood, and overt behaviour. Nonetheless, numerous authors have argued that depression is associated with actions that precipitate stress in the long term (Hammen, 1991; Monroe & Peterman, 1988; Monroe & Simons, 1991; Rutter, 1986). Indeed, in one study, depressed women were found to generate more interpersonal stress in a 1-year period, particularly in an interpersonal context (Hammen, 1991). In that study, depressed women had more life stressors that could be seen as random, but the behavioural choices of the women also contributed to the creation of more difficult circumstances. There is also recent evidence from a very large population-based twin registry that supports the notion that self-generated stress contributes to the onset of depression (Kendler et al., 1999; 2000). What is not well understood is whether the correlation between depression and problematic, potentially stress-generating behaviours is cognitively mediated. That is, do the distortions of depressed individuals lead them to select behavioural strategies that are not optimal, and do these strategies lead eventually to increased stressors or other self-defeating behaviours? These ideas could be tested within presently available experimental paradigms and would be further evidence in positing cognition as a central feature in the experience of depression.

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