These principles of coherence and correspondence apply to autobiographical memory (Conway 2005): memories are sometimes altered to preserve a coherent self as the past is re-written to make sense of current goals and a new self-image.
Distortions exaggerating continuity between previous and present self may also be psychologically adaptive by enhancing self-appraisal and well-being. One instance of the so-called consistency bias is when we interpret the past in the light of the present (see also Dean 2008). People were asked to rate their attitudes towards major social issues, such as whether drugs should be legalised, whether women should obtain equality of treatment, and whether ethnic minorities should be helped. Nine years later, the participants were asked to provide the same ratings again, and also to report what their attitudes had been the first time around. Participants remembered their past attitudes as much closer to their current attitudes than they actually were (Markus 1986).
Consistency biases are not confined to political views, but affect also how people rate their romantic relationships (Scharfe and Bartholomew 1998). Participants were asked to rate the quality and stability of their relationships twice, several months apart, and the second time they were also asked to report what their previous ratings had been. Participants were more accurate in this case than in the study on political attitudes, probably because the time gap was much reduced, but those who reported their previous ratings inaccurately did so in accordance with the consistency bias. For instance, if the relationship got worse, they reported that at the first interview they had rated their relationship less positively than they actually did.
When the consistency bias is applied in the opposite direction, and we adapt not the past to the present, but the present to the past, it is also known as a failure in updating. In some circumstances, people describe their present selves as much more similar to their past selves than they actually are. For instance, people developing a chronic or degenerative disease may continue to view themselves as they were before the onset of the disease, not acknowledging some of the physical or psychological changes. It was found that people with dementia experience a shift in personality as a result of their condition, becoming more aloof, introverted, unassured, and submissive (Rankin et al. 2005). However, they do not necessarily have awareness of such changes and tend to underestimate how unassured and submissive they have become.
A more widespread bias is the general tendency towards self-enhancement and self-improvement that seems to affect memory in clinical and non-clinical populations alike. Here are some examples. After taking a study skill class, people asked about their performance exaggerated how bad it was before the class, and how good it was after the class, in order to lend support to the view that the class had helped them improve their skills (Conway and Ross 1984). In patients with brain damage, recollections of the past are distorted in such a way as to present their past selves in a better light. One hypothesis put forward by Fotopoulou (2008) is that self-enhancing memories have positive effects on mood regulation: by putting a positive spin on their experiences, people feel better about themselves, with some clinical and pragmatic advantages. Fotopoulou acknowledges also the costs of confabulation. Stories that depart from reality "create significant difficulties in patients’ social environment”.
In a review article on self-enhancement, Alicke and Sedikides (2009) summarise the main costs and benefits of this pervasive tendency. They argue that there are significant physical and psychological health benefits, in terms of stress reduction, active coping, purpose in life, personal growth, resilience, and subjective well-being. Self-enhancers are also unlikely to experience anxiety, neuroticism, and depression. Presenting oneself in a positive light is generally beneficial and leads to success and satisfaction in interpersonal relationships. When self-enhancement tendencies are exaggerated, though, they carry considerable costs. People who are immodest and arrogant are disliked and socially sanctioned.
Schacter and Addis (2007) also find that optimism is generally correlated with reduced stress and good physical and psychological health, but they offer a more detailed account of the possible costs. There are situations in which a tendency to view things in an excessively positive light may be an obstacle to achieving goals as people are not prepared for failure and cannot “respond effectively to setbacks”. Moreover, optimism may engender risky behaviour driven by the false belief that “everything will be alright” and may bring about disappointment if things do not turn out as well as expected. A more realistic attitude is beneficial when important goals are at stake and when the chances of success in achieving one’s goals are low.