Sunday, July 13, 2014

Book Review: The Invisible Gorilla by Christopher Chabris and Daniel Simons

The book "The Invisible Gorilla" should be required reading for anyone who is called as a witness in a court case, or called for Jury service at one, and also for everyone who drives a car or flies an aircraft.

The human brain is an excellent device for spotting patterns, but sometimes we get so focussed on spotting particular patterns that we think we see ones which are not really there - the original hunt for witches being the classic example - or equally dangerous, filter out real information we need to know because we are looking for something else.

In one of the "Father Brown" stories G.K. Chesterton had his clerical sleuth solve a murder committed by a "mentally invisible man" - a postman who all the witnesses ignored because they tuned him out of their perceptions - he was just a postman.

Chabris and Simons' book demonstrates how, to a truly frightening extent, we make that kind of mistake far more often than we realise.

The book starts with an account of how a Boston policeman, Kenny Conley, was sent to jail because a jury convictem him of perjury and obstruction of justice: Conley, who was white, was one of a number of officers converging on a murder suspect from different directions. The suspect attempted to evade pursuit by climbing a fence. The closest police officer, who like the suspect is african-american and who was wearing plain clothes, attempted to apprehend the suspect while he was climbing the fence, but fell, and was then himself attacked and assaulted by several uniformed white police officers who apparently mistook their colleague for the suspect. Conley climbed the fence in hot pursuit of the suspect within yards of where this beating was taking place, pursued him for a mile, and did in fact arrest the suspect who all the officers involved had been pursuing.

When there was an inquiry into the assault on the plainclothes cop, Conley claimed on oath not to have seen the beating. When it was established that he had in fact passed very near to that incident, neither prosecutors nor the jury could believe that he was not lying to protect his fellow officers.

After Conley's release from jail a Boston journalist, Dick Lehr, who had originally been of the same opinion, brought Conley to see the authors of the book, because he had begun to have second thoughts about whether Conley might have been so focussed on the suspected criminal that he failed to notice an assault taking place almost under his nose.

The authors produce a huge amount of convincing evidence that most of us make exactly that kind of mistake on a frighteningly regular basis, even when we sometimes put our lives at risk or may vote to send innocent people to jail in consequence. When we are focussed on observing one thing, we can sometimes miss other events, some of which might be serious threats, to a greater extent than we might think possible. And worse, we don't realise we have missed them: we can't believe we could have been looking right at something and fail to see it.

The title of the book is taken from the "Gorillas in our midst" experiment which the authors had made: they found that when a group of test subjects is set to watch a film of a basketball game and carry out some moderately attention-demanding task such as count the number of passes in the game, about 50% of them will not even notice if a person in a gorilla suit walks through the basketball court, faces the camera, beats her chest, and walks on.

If you are having trouble believing this, look at the website for this book at

where there is a version of the gorilla video and some similar tests and material, which does not take long to view and is utterly convincing.

But when the experiment was first performed, those who didn't notice were not just shocked at what they had missed: when they were shown the film again they were so convinced that what they had not noticed before could not have been there that they accused the experimenters of switching the tape.

A very important part of this book for those of us who drive is the section on how our failure to notice things can put us at increased risk of accidents, and this book changed my opinion on the reasons for the accident rates for cyclists and riders of motorbikes.

Until I read "The Invisible Gorilla" I was aware of the high accident rate involving motorbikes but believed that the main reason for this was the propensity of some motorbike riders to drive in a more risky way. After reading this book I was compelled to modify my views and recognise that some of the increased accident rate for motorbikes may be down to car drivers' mistakes, particularly a failure to spot motorbikes when the drivers concerned thought they were looking out for other traffic but were really focussed on looking for cars and lorries.

This book is an incredibly useful study, written in accessible and entertaining language, into the way our minds and perceptions focus on the things we think we need to know, so that we are not swamped by all the potential observations which surround us every waking moment, but how this can sometimes lead us to ignore things we really need to notice. And not to notice that we have done so.

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