The Invisible Gorilla

Tom Shipka

In 1997 two psychologists designed an experiment in which they directed a group of volunteers to view a film that lasted less than a minute in which people assembled in a circle pass a basketball to one another. The viewers were asked to count the exact number of passes. Because they focused their attention on the movement of the ball, over half of them failed to notice something that they didn't expect. Midway through the film, a person dressed in a gorilla suit walked through the circle, stopped, faced the camera, beat its chest, and walked off, spending a full nine seconds in the film. The experiment has been repeated hundreds of times with the same results. (1) Recently, the two psychologists, Christopher Chabris and Daniel Simons, published a book which expands on the gorilla experiment. Entitled The Invisible Gorilla: How Our Intuitions Deceive Us, (2) it demonstrates that all of us are victims of six illusions – attention, memory, confidence, knowledge, cause, and potential.

In the illusion of attention, highlighted in the gorilla experiment, we assume that we see far more of our visual field than we actually do. (3) In this connection, the authors urge people to discontinue the use of both hand-held and hands-free cell phones while driving because studies show that using a cell phone dramatically impairs our ability to perceive unexpected events. (4)

In the illusion of memory, we assume that we remember the past far more accurately than we actually do. (5) For instance, a former basketball player at Indiana University vividly remembered that Coach Bobby Knight had choked him in a rage of anger at a practice but a videotape of the event which surfaced later contradicted the player's story. (6)

In the illusion of confidence, we assume that self-assured people are competent people. (7) Studies show, however, that "the confidence that people project, whether they are diagnosing a patient, making decisions about foreign policy, or testifying in court" is no guarantee that they are as well-informed as they believe. (8)

In the illusion of knowledge, we assume that we know more about a topic than we usually do, whether we're talking about a bicycle, a toilet, a car, or a computer. If we're pressed for explanations, we usually come up short. (9)

In the illusion of cause, we mistake correlation with causality. (10) For instance, because many autistic children are first diagnosed soon after their vaccinations for measles, mumps, and rubella, many parents refuse to have their children vaccinated, despite the fact that dozens of studies with hundreds of thousands of children show that there is no causal link between autism and vaccinations. (11)

Finally, in the illusion of potential, we assume that "simple tricks can unleash the untapped potential" in our minds. (12) For instance, many parents play classical music to their babies to enhance their IQ, despite the fact that there is no scientific evidence to support such a belief. (13)

In a nutshell, then, Christopher Chabris and Daniel Simons challenge all of us to be on the lookout for the invisible gorillas, the everyday illusions that haunt us. To succeed, of course, we must first acknowledge that they exist.


  1. This experiment demonstrates "Inattention blindness," our tendency to miss unexpected objects in our surroundings because our attention is directed elsewhere. When this film was shown at a conference that I attended in Las Vegas in January 2005, most of the audience, myself included, missed the gorilla.
  2. Broadway Paperbacks, 2009.
  3. The Invisible Gorilla, p. 7.
  4. The Invisible Gorilla, p. 25.
  5. The Invisible Gorilla, p. 241.
  6. The Invisible Gorilla, p. 73.
  7. The Invisible Gorilla, p. 231.
  8. The Invisible Gorilla, p. 82. In fact, the authors contend that "the most incompetent among us tend to be the most overconfident." (p. 95) An example of unjustified confidence that the authors use is George Tenet's answer to President George W. Bush's question as to whether Saddam Hussein really had weapons of mass destruction. Tenet replied: "It's a slam dunk." As it turned out, Tenet was wrong. (p. 95)
  9. The Invisible Gorilla, pp. 121-123.
  10. The Invisible Gorilla, pp. 231.
  11. The Invisible Gorilla, pp. 174-176, p. 179. The authors note that "Despite the now-overwhelming evidence that vaccinations are not at all associated with autism, 29 percent of people in our national survey agreed with the statement 'vaccines given to children are partly responsible for causing autism.'" (p. 183)
  12. The Invisible Gorilla, p. 242.
  13. The Invisible Gorilla, pp. 185-197.

© 2012 Tom Shipka