The Invisible Gorilla


The Invisible Gorilla

Authors: Christopher Chabris and Daniel Simons


This book is an exposé of human cognitive weaknesses. The authors discuss what they call everyday illusions which greatly impact our lives (page x). They explore the ways our faculties fail us, and demonstrate our profound unawareness of these shortcomings. We see how most people are surprised to discover how vulnerable they are to these “critically important limitations on our cognitive abilities” (page 7).

The authors focus on human weaknesses that hinder our perception, attention, memory, knowledge and understanding. They support their arguments with several classic psychological experiments; the gorilla experiment, which they devised, is perhaps the most striking. In this experiment, participants are asked to count how many times a group of people pass a ball between them. Part way through this, a person dressed in a gorilla suit dances through the scene, waving to the camera. Most participants in this experiment fail to notice the gorilla-suited man, their attention completely focused on their task.

This experiment uncomfortably demonstrates the limits of visual perception, and the authors discuss the impact of this type of inattentional blindness in real life. Radiologists, for example, incorrectly read images, teachers miss overt bullying, and intelligence officials overlook evidence of terrorist planning (pages 34 and 40).

Pink spinning illusion 2. Justin Hanes Magician, Al... on Flikr.
Pink spinning illusion 2. Justin Hanes Magician, Al… on Flikr.

The illusion of memory is perhaps as intriguing as that of visual perception. The book shows how people’s recollection of previous events may be mistaken, even when these are vivid, flashbulb, memories. This is important because, unfortunately, ‘… people regularly use vividness and emotionality as an indicator of accuracy…’ (pages 75 and 79). The authors review other illusions of memory such as change blindness (page 60), failure of source memory (page 63), and memory revision (page 66).

In their discussion of the illusion of confidence, the authors point out that overconfidence is typically seen in the less competent. They refer to the term unskilled-and-unaware, coined by Justin Kruger and David Dunning, to describe this phenomenon (pages 86-89). They show the widespread impact of this illusion, for example in medicine where patients may rely unquestioningly on confident but incompetent doctors (page 107). The illusion of confidence applies as much to groups as to individuals, and the book authors discuss how this influences their decision-making and choice of leaders (page 98). The authors believe that increasing people’s competence is an effective way of countering this illusion (page 90).

The book is replete with interesting anecdotes which the authors use to illustrate their points. For instance, they use the story of policeman Kenny Conley to demonstrate inattentional blindness; he was wrongly convicted for failing to witness a crime committed in his presence (page 9). They refer to Hillary Clinton who wrongly recollected the context of her trip to Bosnia, painting it in more heroic circumstances than it really happened (page 77). They also cite Scott Waddle, captain of the submarine Greenville, who became infamous for failing to see a fishing ship sinking directly ahead of him (page 13). Relevant to medicine, they remark on Andrew Wakefield, the doctor who convinced many people of his fraudulent research linking the MMR vaccine to autism (pages 174-184).


This book discusses important human factors that influence all aspects of our lives. The authors are at the forefront of the field as researchers, and use very illustrative examples to support their arguments. The book is very well-written and it makes a valuable addition to other texts which address similar topics such as Being WrongIrrationality, The Drunkard’s Walk, and Subliminal. The book’s advantage however is its focus on a limited number of illusions, allowing the authors to explore these in great detail.


Human factors are critical to health care, and all the illusions the book discusses are relevant to doctors’ practice. Awareness of these human traps, and knowing how to avoid them, is central to patient safety, and I highly recommend it.

  • Publisher, Place, Date: Harper Collins, London, 2010
  • Number of chapters: 6
  • Number of pages: 306
  • ISBN: 978-0-00-731731-8
  • Price: £8.99
  • Rating: 4 stars


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