As a scientist who interacts a lot with the general public, I am often asked to explain phenomena that lay people have observed. I used to take those observations at face value and was often stumped at coming up with an explanation because of the inconsistent elements the observations seemed to contain. But I have found from experience that what people tell me they ‘saw’ is not purely raw observational data but that when you go back and actually repeat the situation, the observations are different from what was originally reported and that much of the paradoxical elements go away.

This raises an important point. In investigating and explaining any phenomenon, we first have to check if what we saw was ‘real’.

The problem is that our brain’s first reaction is dominated by what Daniel Kahnemann in his excellent book Thinking Fast and Slow (2011) calls ‘System 1’ thinking. What happens is that when people ‘see’ something, their brain immediately kicks in and they try to makes sense of what they saw by subtly shaping the data to fit into a plausible narrative. It is this manipulated data that they are convinced they saw and which they then report later. Reporting it cements the distorted version even further into their memory making them even more convinced of its truth. Magicians use this feature of our brains to fool us into thinking that we saw something that was more amazing than it really was.

For example, in response to my post on the Ponzo illusion, commenter Molly said that she had assumed that the moon’s larger size on the horizon was due to the atmosphere acting as a magnifying lens. In this case, she knew that the moon was not actually bigger but she thought that the image of the moon had actually been magnified before she saw it. Hence Molly looked for the cause outside her head and came up with a plausible explanation.

If she had reported to me that she had observed that the image of the moon was more magnified on the horizon than at its zenith and asked me the reason for it, and I had accepted her observations at face value (after all, why would she lie?), I likely would have come up with an explanation similar to hers. But the image of the moon was not actually magnified (as can be confirmed by a simple test) and the effect lay inside her head, by her brain intervening to do some processing even before she become conscious of what she saw.

This interplay of outside stimuli and brain manipulation happens all the time and it takes quite a lot of effort to distinguish between actual observations and subsequent inferences. Sometimes it may be impossible, if the manipulation is hardwired into the brain as is the case with the Ponzo illusion. This is why two people’s recollections of a conversation or event that they both took part in can be quite different and why eyewitness accounts of crimes are notoriously unreliable unless the witness immediately jots down notes of what they saw before their brains can massage the information too much in trying to make sense of it. This is also why journalists should take notes of events and interviews to prevent later distortions creeping in.

Once you are more aware of your brain’s ability to unconsciously manipulate inputs and memories in its effort to create coherence and to tie in with prior beliefs and knowledge, you become better able to take precautions to prevent it, though I doubt that we are ever totally successful.