Cognitive biases and their role in intrusive thoughts

What is cognitive bias?

Cognitive bias is an error in judgment that occurs when people make decisions quickly and with little thought. This can help people decide swiftly but can also cause less-than-perfect choices.

In his best-seller, Thinking Fast and Slow, Daniel Kahneman, a psychologist, refers to two distinct types of thinking.

  • System 1: fast, automatic thinking, and
  • System 2: slower, more purposeful thoughts.

I find it helpful to think of a learner driver as having to use slow, purposeful thought to make the car move without kangaroo jumps. Serious attention is needed as the person learns to drive. Still, over time, this tough act becomes fast and automatic to the extent the person can carry on a conversation and seamlessly make the car move smoothly.

Every day, a constant overload of information bombards us, and it is impossible to interpret each piece of information to make a decision accurately.

For example, if you are driving and approaching traffic lights, your brain can focus on the necessary information and filter out the rest. It takes seconds to approach the lights; you do not need to analyse and interpret information regarding two people chatting outside a shop. Your brain can filter out irrelevant information to save processing power and dedicate all resources to what you need to do to negotiate the traffic lights safely.

Hopefully, you can see why the brain needs to create shortcuts and make sense of the world quickly, as the attention required when learning a new skill would be cumbersome to perform everything a person does during the day.

These rules of thumb or heuristics help you function without analysing all incoming information. However, these mental shortcuts can lead to bias.

As noted in The Atlantic, most people think of race or gender when they hear or read the word bias. But the brain, to be efficient, can produce cognitive bias or errors in how we think and make decisions.

The rest of the article shall note well-known cognitive biases and focus on the bias relevant to intrusive thoughts.

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Common cognitive biases

The confirmation bias

Confirmation bias is a cognitive bias that leads people to favour information that confirms their beliefs and ignore information that conflicts with their opinions or views.

The hindsight bias

The hindsight bias, also called the ‘I knew it all along’ bias, happens when people perceive actual outcomes as expected but only after the fact.

For example, insisting that you knew what team would win a football match once the game was over and the winning team was announced.

The anchoring bias

The anchoring bias can occur when a person decides based on the first piece of information they were presented with. For example, if the salesman tells you the car you are looking at is priced at £15000, you are more likely to pay this figure than if the salesman said the vehicle is £10000.

The misinformation effect

The misinformation effect happens when a person’s memory of an event is less reliable due to post-event information. For example, participants were shown a video of a car accident in a study.

Some participants were then asked about the speed of the cars before the crash, while others were asked about the speed of the cars after the crash.

The results showed that those who were asked about the speed of the cars before the crash remembered it more accurately than those who were asked afterwards.

The false consensus effect

The false consensus effect is a cognitive bias that occurs when people believe they have the same beliefs, attitudes, and values as those around them.

The halo effect

The halo effect is a cognitive bias where the positive impressions of the person or company influence people.

For example, if you like a specific person, and they are selling a product or endorsing a political candidate, you might feel more inclined towards the product or political candidate based on your liking for the figure.

The self-serving bias

Refers to attributing our actions to external influences and other people’s actions to internal ones. For example, if a person fails a test, it is because the test was too hard, whereas others fail. After all, they did not work hard enough.

The availability heuristic

The availability heuristic is a cognitive bias that leads to poor decision-making. This bias is related to an error in memory, with over-emphasis on one type of memory (for example, a person thinking there are more male celebrities than women).

When we rely too heavily on this biased memory, it can distort our view of the world and lead us to make poor decisions.

Inattentional blindness

Inattentional blindness, sometimes called perceptual blindness, is a phenomenon where people cannot notice a stimulus in plain sight.

This can be because the individual’s attention is directed elsewhere or because the stimulus is not conspicuous enough.

The invisible gorilla experiment is a famous example of inattentional blindness. In this experiment, participants were asked to watch a video of two teams of basketball players passing a ball back and forth.

They were instructed to count how many times one group passed the ball between themselves. Near the end of the video, a person in a gorilla suit walks across the screen.

Most participants did not notice the gorilla at all.

The optimism bias

The optimism bias is a cognitive bias that causes us to overestimate the likelihood of good things happening to us.

Cognitive biases relevant to intrusive thoughts and OCD

Having an understanding of the role of cognitive bias in OCD can shed light not only on how intrusive thoughts develop but also on how they are maintained.

The biases of note are attentional biases, where the person focuses more on threat-related information through selective attention and interpretive bias, where the person can decide quickly if something is a threat to them.

According to Rachman 1997, (1) catastrophic misinterpretations of the personal significance of intrusive thoughts are the leading cause of the development and maintenance of obsessions.

Consequently, people with OCD tend to see themselves as, for example, immoral, dangerous, or sinners because of having intrusive thoughts, even though in reality, they have never acted on their thoughts or done something that warrants such negative self-descriptions. This concept is called thought-action fusion.

Thought-action fusion

Thought-action fusion, where the person gives too much importance to the thought, consists of two parts.

  • Morality – where the person believes that having intrusive thoughts is just as bad as carrying out the thought, and
  • Likelihood – believing that the thought itself increases the probability of carrying out the thought.

For example, suppose the person is religious and has intrusive thoughts of shouting something obscene during a religious service. In that case, the person views themselves as morally repugnant, even though they did not in fact, shout out anything during the service.

The main difference between someone who has an intrusive thought and can ignore it and someone who starts to obsess about it is how they interpret it.

Read more on thought-action fusion.

The following cognitive distortions are prevalent among people who may struggle with intrusive thoughts and OCD.

Tolerance of uncertainty – It is essential to consider all possible situation outcomes.

Threat estimation-Things around me are unsafe.

Control of thoughts-I should be able to rid my mind of intrusive thoughts

Importance of thoughts-Having evil thoughts means I am a terrible person

Responsibility-I am responsible for outcomes

Perfectionism-If I don’t do it perfectly, people won’t respect me.

Overcoming cognitive biases

Cognitive Behavioural Therapy (CBT) can help you overcome biases and distortions underlying OCD. Read more on CBT for Intrusive thoughts.


  1. Rachman S. A cognitive theory of obsessions. Behav Res Ther. 1997 Sep;35(9):793-802. doi: 10.1016/s0005-7967(97)00040-5. PMID: 9299799.
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