What is the Optimism Bias?
More than 90% of academics rate themselves as above-average teachers . College students think they are more likely than their peers to experience positive events, such as living past eighty or having a mentally gifted child, but less likely to experience negative events such as divorce . Clearly, they can’t all be right; not everyone can be above average. But a tendency to hold beliefs that are biased in favour of positive outcomes –the optimism bias– is seen in many different aspects of human thought, and has been extensively investigated by Dr Tali Sharot, cognitive neuroscience researcher at University College London. The above examples, termed the “superiority illusion” and “unrealistic optimism” respectively are just two of many forms of the optimism bias.
So what happens when we’re faced with evidence against our optimistic beliefs? Dr Sharot’s research  suggests the optimism bias may be maintained from a selective belief-update process that favours positive over negative information. In a recent study, participants were first asked how likely it was that they would experience an adverse life event (e.g., Alzheimer’s disease, or robbery) and then provided general normative statistics of the likelihood of the event before being asked to estimate the likelihood for a second time. The data showed that participants were more likely to adjust their estimates when the average probability of experiencing a negative life event was lower than the participants’ first probability estimate (good news) than in a situation in which the average probability was higher (bad news). To rule out the possibility that participants had simply forgotten the bad information, the researchers administered a memory test on the information given. Information was recalled perfectly well whether it was good or bad, indicating that the optimism bias results specifically from a failure to integrate incoming negative information into the belief system.
This has drastic implications for traditional learning theories, which generally suggest that learning occurs when there is a discrepancy between someone’s expectations about what will happen and the actual outcome of events, regardless of the emotional value it holds . In other words, the greater the absolute difference between expectation and reality, the greater the learning. Sharot’s work on the optimism bias, however, suggests that emotional valence does have an impact, and this insight requires a whole new framework in which to think about learning.
How is this implemented in the brain?
Dr Sharot and colleagues’ then looked to the patterns of fMRI brain activation while their participants were carrying out these belief update tasks. Within the prefrontal cortex, distinct regions were linked to good compared to bad news. The left inferior frontal gyrus (IFG), in particular, was linked to the updating of positive estimation errors, with greater activity in conditions when the information was more positive. By contrast, the right IFG was associated with negative estimation error. The more undesirable this information was relative to participants’ existing beliefs, the lower the activity in this region. It was also found that this correlation between neural activity and estimation error for negative information was diminished in participants who scored highly on a questionnaire assessing optimism, indicating that optimistic people are not as good at representing bad news.
Subsequent research suggested that this frontal activation plays a causal role in the encoding of estimation error valence . Dr Sharot and colleagues used transcranial magnetic stimulation (TMS) to disrupt the activity in different part of the brain. They found that, although disrupting the right IFG did not greatly change participants’ ability to learn from positive or negative information, inhibiting the left IFG led to more learning from bad news. This suggests that this region usually plays a role in inhibiting the ability to learn from bad news.
Why do we have this bias?
Beliefs matter: not only in guiding our decisions, but also in how we perceive and interact with the world. There are some clear advantages of holding positive beliefs, from enhancing exploration and search for the optimal solution, to increasing motivation and vigour so that we are more likely to achieve our goals, and increasing general wellbeing by reducing stress and anxiety. However, if these beliefs differ consistently from reality some problems may arise –driving people to underestimate risk, and thus fail to take precautionary behaviours. It’s hard to see how such biased thinking could be adaptive; so, why do we have it?
The answer may come from the inherent flexibility in belief formation. It has been shown that under high stress conditions, in which participants were told they would be required to give a lecture on a surprise topic, and then judged on this, the optimism bias vanishes . Compared to participants in a low-threat condition (who were told that they would only need to write about a topic, but would not be judged on it), levels of stress-related hormones such as cortisol, and self-reported anxiety were significantly higher. The high-threat group was also better at learning from negative information in a belief-update task, implying that the optimism bias was reduced.
It therefore appears that in general, the optimism bias is a pervasive aspect of human cognition that serves us well in the majority of the situations we encounter. It is by understanding this bias more fully that we may learn how to enhance positive or cautious thought processes and behaviours when the bias is ineffective or problematic. We may then potentially apply this knowledge to a variety of real life problems such as clinical depression and poor financial decision making.
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 Sharot, T., Kanai, R., Marston, D., Korn, C., Rees, G., & Dolan, R. (2012). Selectively altering belief formation in the human brain. PNAS, 17058–17062.
 Garrett, N., González-Garzón, A. M., Foulkes, L., Levita, L. & Sharot, T. (under review). The Optimism Bias Fluctuates in Response to Changes in the Environment. Psychological Science.