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Tricks your brain uses

Thank you for joining me for my fifth blog of the series, highlighting decision-making and the brain. This is my public exploration as to what drives decision-making and how we can use that information to make better decisions. I met old colleagues yesterday, some of whom I had not met for 15 years. It reminded me that, whilst I thought I had remembered them, I was surprised by things that I had forgotten. I will make sure I research memory soon!

Back to our epic journey. Our brain is a decision-making machine that models the world around us to encourage action that increases our chances of survival and reproduction. The world around us is very complex, so our brain simplifies our model of the world to help us react quickly, conserve decision bandwidth and save energy.

Today’s question is, how do we filter the massive input information we receive each moment? Remember, we see in three dimensions and smell, hear and experience time. That is a huge amount of data - imagine how many gigabytes a day’s worth of your data is!

Other ways we make intuitive decisions is by both filtering information we receive and simplifying the nature of problems we respond to, by using subjective, rather than objective information, which makes it easier to answer. BTW, I'm not a downer on human thinking in general, quite the opposite, but how do we operate this ancient machine without a user guide? Consider this a troubleshooting section at the end.

One topic we discussed last week is how we ease our bandwidth by relying on intuitions (Intuitions - can we trust them? (, which is a model of the world we have constructed from our observed data points. We sometimes take a few data points and feel we understand how it works.

One common mistake is to think of cognitive effort as being a purely mental impact. Two notable physical effects can be seen when we try to solve a challenging puzzle 1) our pupils dilate noticeably 2) our heart rate rises.

Dilated pupils indicate engagement

The starting point of simplification can be at source - our senses. Have you ever heard your name being said in a noisy room? How can we filter the noise vs signal to make this happen?

My reading points to our mind constantly looking for deviations from the norms - particularly if it is dangerous. Mostly it looks for cues that we already recognise or are specifically looking for. This means we are not taking in all the information around us and assessing all the information in an unbiased way as I would have initially thought. As an example, when I am looking for a restaurant, I rarely even notice the shops I pass. It is not relevant to my objective - it just doesn’t register and has been filtered out. In that sense we do not use all the information we come across, it is heavily weighted towards what we already recognise or are searching for.

This weighting of information means we can miss out on things that are not very prominent, recognisable or expected. It also means that the model in our head will be simpler, as factors that are not obvious but still have an impact will be excluded.

We filter to save bandwidth

Another type of simplification is when we substitute one question for another. We often do not know we are doing it.

For example, if someone asked you how much terrorism is there in the world, in the absence of hard numbers we might say there is a lot of terrorism. This is because it gets a lot of media attention and evokes quite a fearful response. We are answering a different question, 'how much has terrorism come to your attention'. This is called ‘Availability bias’, we tend to think of something more if it is more commonly in our face.

Availability bias, is where selling ideas come to play. If people are continually told about a problem needing a solution they will back ever more draconian measures to prevent it. Another example of availability bias is thinking that they will have success in the stock market after hearing about a friend’s success.

Whilst availability bias might be a simplifying algorithm for us to decide whether something is worth focusing on, the subjective nature of the way we try and substitute one question to another means we will likely make errors and should try and make sure we use objective information where we can.

Another example of simplification we often make is substituting ‘what are the chances of Trump winning the next election‘ to ‘what do people you know think of him’. This switch of questions allows me to use less mental energy as it can allow me to utilise subjective information again.


Today we have covered examples of how we filter the information that comes from our senses and how we simplify our thought process by answering easier questions. The three take-aways are:

1) We do not take in all the information that comes to us in an unbiased way, we are constantly looking for things that are relevant to us which will make us miss things

2) We are influenced by how easily we can recall things (availability bias), so something in the news appears like it’s happening much more than it might be statistically

3) We easily slip into answering a different question that requires less brain power. We do this without knowing.

Thank you for joining. Next week, I will focus on a topic that is really fascinating to me decision fatigue and decision leverage (which decisions should we focus on).


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