The Invisible Gorilla: And Other Ways Our Intuitions Deceive Us

by Christopher Chabris

  2. In Romania, more than four thousand people contracted measles and ten people died during the outbreak that was the source of the missionary girl’s infection.

  3. Evidence that people can recognize their friends by their gait alone comes from J. E. Cutting and L. T. Kozlowski, “Recognizing Friends by Their Walk: Gait Perception Without Familiarity Cues,” Bulletin of the Psychonomic Society 9 (1977): 353–356. Evidence that people can judge teachers from a brief glimpse comes from N. Ambady and R. Rosenthal, “Half a Minute: Predicting Teacher Evaluations from Thin Slices of Nonverbal Behavior and Physical Attractiveness,” Journal of Personality and Social Psychology 64 (1993): 431–441.

  4. Examples of pareidolia discussed in this section come from the following sources: Associated Press, “‘Virgin Mary Grilled Cheese’ Sells for $28,000,” November 23, 2004 (www.msnbc.msn.com/id/6511148/); “Jesus Seen in Cheese Snack,” CNN.com, May 18, 2009 (www.cnn.com/video/#/video/living/2009/05/18/pkg.tx.cheese.snack.jesus.KTXA); “Message from Allah ‘in Tomato,’” BBC News, September 9, 1999 (news.bbc.co.uk/2/hi/uk_news/443173.stm). Other religious pareidolia examples are summarized by Wikipedia, en.wikipedia.org/wiki/Perceptions_of_religious_imagery_in_natural_phenomena (accessed May 28, 2009).

  5. This experiment is reported in N. Hadjikhani, K. Kveraga, P. Naik, and S. Ahlfors, “Early (M170) Activation of Face-Specific Cortex by Face-like Objects,” Neuroreport 20 (2009): 403–407. The researchers showed their subjects pictures from an entertaining book that contains nothing but “found” images of faces in other common objects: F. Robert and J. Robert, Faces (San Francisco: Chronicle Books, 2000).

  6. K. Stollznow, “Merchandising God: The Pope Tart,” The Skeptic (Autumn 2000): 28–34. The winning bid turned out to be a hoax, so Stollznow donated the Pope Tart to the second-highest bidder, a radio station DJ in Texas.

  7. The experiments are reported in D. A. Redelmeier and A. Tversky, “On the Belief That Arthritis Pain Is Related to the Weather,” Proceedings of the National Academy of Sciences 93 (1996): 2895–2896. According to these authors, modern medical textbooks downplay any relationship between the weather and arthritis pain. More recent studies have agreed in finding little to no connection, e.g., F. V. Wilder, B. J. Hall, and J. P. Barrett, “Osteoarthritis Pain and Weather,” Rheumatology 42 (2003): 955–958. The 1972 survey of arthritis patients is from D. F. Hill, “Climate and Arthritis in Arthritis and Allied Conditions,” in A Textbook of Rheumatology (8th ed.), ed. J. L. Hollander and D. C. McCarty, 256–263 (Philadelphia: Lea and Feringer, 1972) (as described by M.S. Shutty Jr., G. Cundiff, and D.E. DeGood, “Pain Complaint and the Weather: Weather Sensitivity and Symptom Complaints in Chronic Pain Patients,” Pain 49 [1992]: 199–204). This tendency to see patterns we expect even when they aren’t present has been known for more than forty years. It can even interfere with our ability to see patterns that actually are present but are unexpected. The seminal research on the effects of expectations on pattern perception involved the use of the Rohrshach “ink blot” test to categorize psychiatric patients as homosexual; see L. J. Chapman and J. P. Chapman, “Illusory Correlation as an Obstacle to the Use of Valid Psychodiagnostic Signs,” Journal of Abnormal Psychology 74 (1969): 21–28.

  8. Examples of correlations like this one, with a clear noncausal interpretation that makes much more sense than any causal one, can be found in almost every introductory psychology textbook (we use Psychology by Scott Lilienfeld and three coauthors). However, we have not been able to find a study in which this particular correlation was actually mea sured!

  9. BBC News, “Sex Keeps You Young,” March 10, 1999 (news.bbc.co.uk/2/hi/health/294119.stm). For details of the original study, see D. Weeks and J. James, Secrets of the Superyoung (New York: Villard Books, 1998).

  10. The headlines cited in this section and the research underlying them included the following sources: Headline from CNN.com, “Drop That BlackBerry! Multitasking May Be Harmful,” August 25, 2009 (www.cnn.com/2009/HEALTH/08/25/multitasking.harmful/index.html). For the original study, see E. Ophir, C. Hass, and A. D. Wagner, “Cognitive Control in Media Multitaskers,” Proceedings of the National Academy of Sciences, 2009. Headline from Reuters Health, “Bullying Harms Kids’ Mental Health: Study,” February 6, 2008 (www.reuters.com/article/healthNews/idUSCOL67503120080206). For the original study, see L. Arseneault, B. J. Milne, A. Taylor, F. Adams, K. Delgado, A. Caspi, and T. E. Moffitt, “Being Bullied as an Environmentally Mediated Contributing Factor to Children’s Internalizing Problems: A Study of Twins Discordant for Victimization,” Archives of Pediatrics and Adolescent Medicine 162 (2008): 145–150. The article compared twins at age ten, of whom one had been bullied between ages seven and nine and one had not been bullied. Headline from MindHacks blog, “Does Your Neighborhood Cause Schizophrenia?” by Vaughn Bell, July 5, 2007, www.mindhacks.com/blog/2007/07/does_your_neighbourh.html (accessed June 1, 2009). The blog post and subsequent comments discuss various models in which environmental factors might contribute in a causal way to rates of schizophrenia, although the study itself was not a random-assignment experiment and does not permit that conclusion. For the original study, see J. B. Kirkbride, P. Fearon, C. Morgan, P. Dazzan, K. Morgan, R. M. Murray, and P. B. Jones, “Neighborhood Variation in the Incidence of Psychotic Disorders in Southeast London,” Social Psychiatry and Psychiatric Epidemiology 42 (2007): 438–445. Headline from BBC News Online, “Housework Cuts Breast Cancer Risk,” December 29, 2006 (news.bbc.co.uk/2/hi/health/6214655.stm). For the original study, see P. H. Lahmann et al., “Physical Activity and Breast Cancer Risk: The European Prospective Investigation into Cancer and Nutrition,” Cancer Epidemiology Biomarkers and Prevention 16 (2007): 36–42. Headline from Associated Press, “Sexual Lyrics Prompt Teens to Have Sex,” by L. Tanner, August 6, 2006 (www.sfgate.com/cgi-bin/article.cgi?f=/n/a/2006/08/06/national/a215010D94.DTL). For details of the original study, see S. C. Martino, R. L. Collins, M. N. Elliott, A. Strachman, D. E. Kanouse, and S. H. Berry, “Exposure to Degrading Versus Nondegrading Music Lyrics and Sexual Behavior Among Youth,” Pediatrics 118 (2006): 430–441.

  11. D. T. Max, “The Unfinished: David Foster Wallace’s Struggle to Surpass ‘Infinite Jest,’” The New Yorker, March 9, 2009, pp. 48–61 (www.newyorker.com/reporting/2009/03/09/090309fa_fact_max). For a discussion of some methods of inferring causation without conducting experiments, see: S. G. West, “Alternatives to Randomized Experiments,” Current Directions in Psychological Science 18 (2009): 299–304.

  12. J. M. Keenan, S. D. Baillet, and P. Brown, “The Effects of Causal Cohesion on Comprehension and Memory,” Journal of Verbal Learning and Verbal Behavior 23 (1984): 115–126. Reading sentences that require a causal inference also produces increased brain activity in a range of regions that differs from those activated by reading pairs of sentences that do not require an inference. See G. R. Kuperberg, B. M. Lakshmanan, D. N. Caplan, and P. J. Holcomb, “Making Sense of Discourse: An fMRI Study of Causal Inferencing Across Sentences,” Neuroimage 33 (2006): 343–361.

  13. R. B. Cialdini, “What’s the Best Secret Device for Engaging Student Interest? The Answer Is in the Title,” Journal of Social and Clinical Psychology 24 (2005): 22–29; C. Heath and D. Heath, Made to Stick: Why Some Ideas Survive and Others Die (New York: Random House, 2007). Heath and Heath discuss this idea extensively in the course of giving advice on how to create and communicate memorable messages.

  14. From The Simpsons, Episode 723, “Much Apu about Nothing,” first aired May 5, 1996 (www.thesimpsons.com/episode_guide/0723.htm).

  15. From U.S. Supreme Court oral arguments on April 29, 2009, in Northwest Austin Municipal Utility District No. 1 v. Holder (No. 08–322). Official transcript available from www.supremecourtus.gov/oral_arguments/argument_transcripts.html (accessed June 22, 2009).

  16. Although randomized experiments are occasionally conducted in the area of public policy, often to test the presumed effects of financial incentives, they are the exception to the rule that most laws
and regulations are passed based on assumptions that they will change behavior, rather than on evidence that they will. For discussion, see Chapter 3 of I. Ayres, Super Crunchers: Why Thinking-by-Numbers Is the New Way to Be Smart (New York: Bantam Books, 2007).

  17. For a keen analysis of this problem in the business literature, see P. Rozenweig, The Halo Effect … and the Eight Other Business Delusions That Deceive Managers (New York: Free Press, 2007). The problems of the Hush Puppies story are discussed in C. Thompson, “Is the Tipping Point Toast?” Fast Company, January 28, 2008 (www.fastcompany.com/magazine/122/is-the-tipping-point-toast.html).

  18. All Chris Matthews quotes come from transcripts of Hardball, retrieved from Lexis/Nexis.

  19. The story of Sherry Lansing is discussed in L. Mlodinow, “Meet Hollywood’s Latest Genius,” The Los Angeles Times, July 2, 2006. See also C. Eller, “Paramount CEO Brad Grey Signs on for Five More Years,” The Los Angeles Times, January 8, 2009 (articles.latimes.com/2009/jan/08/business/fi-grey8).

  20. Statistics from the Centers for Disease Control: www.cdc.gov/ncbddd/Autism/faq_prevalence.htm (accessed June 20, 2009) and www.cdc.gov/mmwr/preview/mmwrhtml/ss5810a1.htm (accessed December 23, 2009).

  21. Details about Andrew Wakefield and the subsequent media attention to the alleged link between the MMR vaccine and autism are drawn from a comprehensive book by Paul Offit published in 2008 by Columbia University Press: Autism’s False Prophets: Bad Science, Risky Medicine, and the Search for a Cure. The book documents the history of alleged cures and causes of autism, pointing out how false causes have been promulgated by the media. It is essential reading for anyone whose child has been diagnosed with autism and anyone who has questions about the risks of vaccines.

  22. A. J. Wakefield et al., “Ileal-Lymphoid-Nodular Hyperplasia, Non-specific Colitis, and Pervasive Developmental Disorder In Children,” Lancet 351 (1998): 637–641.

  23. Wakefield’s quote is from Offit (Autism’s False Prophets, p. 20).

  24. Offit (Autism’s False Prophets, p. 55; emphasis in original).

  25. Use of the MMR vaccine ceased in Japan in 1993 (for reasons unrelated to autism), but there was no decrease in autism diagnoses afterward. See H. Honda, Y. Shimizu, and M. Rutter, “No Effect of MMR Withdrawal on the Incidence of Autism: A Total Population Study,” Journal of Child Psychology and Psychiatry 46 (2005): 572–579. One epidemiological study examined all children born in Denmark between 1991 and 1998 (over 500,000 children) and found no difference in the rates of autism for those who had received the MMR vaccine and those who had not: K. M. Madsen, A. Hviid, M. Vestergard, D. Schendel, J. Wohlfahrt, P. Thorsen, J. Olsen, and M. Melbye, “A Population-Based Study of Measles, Mumps, and Rubella Vaccination and Autism,” New England Journal of Medicine 347 (2002): 1477–1482. Other epidemiological studies find the same result, with no association between vaccination and autism or between the timing of vaccinations and autism. For details, see L. Dales, S. J. Hammer, and N. J. Smith, “Time Trends in Autism and in MMR Immunization Coverage in California,” Journal of the American Medical Association 285 (2001): 1183–1185; B. Taylor, E. Miller, C. P. Farrington, M.-C. Petropoulos, I. Favot-Mayaud, J. Li, and P. A. Waight, “Autism and Measles, Mumps, and Rubella Vaccine: No Epidemiological Evidence for a Causal Association,” Lancet 353 (1999): 2026–2029; C. P. Farrington, E. Miller, and B. Taylor, “MMR and Autism: Further Evidence Against a Causal Association,” Vaccine 19 (2001): 3632–3635; and E. Fombonne, R. Zakarian, A. Bennett, L. Meng, and D. McLean-Heywood, “Pervasive Developmental Disorders in Montreal, Quebec, Canada: Prevalence and Links with Immunizations,” Pediatrics 118 (2006): e139–e150. Andrew Wakefield’s claims of an association between MMR and autism later became embroiled in controversy over such issues as how the initial study was funded and how the patients were selected; see Brian Deer, “Focus: MMR—The Truth Behind the Crisis,” The Sunday Times (London), February 22, 2004. That year, most of the original paper’s twelve coauthors, but not Wakefield, published a retraction of the suggestion that their findings could support a causal connection between MMR vaccination and autism. See S. H. Murch et. al., “Retraction of an Interpretation,” Lancet 363 (2004), 750.

  26. Heath and Heath, Made to Stick.

  27. D. Ansen, “Pulp Friction,” Newsweek, October 13, 2003.

  28. V. S. Ramachandran and S. Blakeslee, Phantoms in the Brain: Probing the Mysteries of the Human Mind (New York: Harper Perennial, 1999), xiii.

  29. Jenny McCarthy quotes are from an interview on CNN Larry King Live, September 26, 2007. Describing her initial research process, McCarthy said she “went online, researched, I typed in Google and then autism.”

  30. Paul Offit quotes are from National Public Radio Morning Edition, December 11, 2008.

  31. Quotes in this paragraph are from an essay by Jenny McCarthy and Jim Carey: “Jenny McCarthy: My Son’s Recovery from Autism,” CNN.com, April 4, 2008 (www.cnn.com/2008/US/04/02/mccarthy.autismtreatment).

  32. For a detailed history of purported cures for autism that have proven to be nothing but snake oil, see Offitt (Autism’s False Prophets). For evidence on the genetic bases of autism, see R. Muhle, S. V. Trentacoste, and I. Rapin, “The Genetics of Autism,” Pediatrics 113 (2004): e472–e486. For evidence on the differential brain development of children with autism, see E. DiCicco-Bloom, C. Lord, L. Zwaigenbaum, E. Courchesne, S. R. Dager, C. Schmitz, R. T. Schultz, J. Crawley, and L. J. Young, “The Developmental Neurobiology of Autism Spectrum Disorder,” Journal of Neuroscience 26 (2006): 6897–6906. For a compilation of many studies examining the effectiveness of behavioral interventions, see J. M. Campbell, “Efficacy of Behavioral Interventions for Reducing Problem Behaviors in Autism: A Quantitative Synthesis of Single-Subject Research,” Research in Developmental Disabilities 24 (2003): 120–138. See also the following report from the American Academy of Pediatrics: S. M. Myers, C. P. Johnson, and Council on Children with Disabilities, “Management of Children with Autism Spectrum Disorders,” Pediatrics 120 (2007): 1162–1182. The possibility that McCarthy’s son Evan was misdiagnosed and never actually had autism was suggested by Dr. Daniel Rubin in a letter to the editor of Neurology Today, a publication of the American Academy of Neurology: D. B. Rubin, “Fanning the Vaccine-Autism Link,” Neurology Today 8 (2008): 3, www.neurotodayonline.com/pt/re/neurotoday/pdfhandler.00132985–200808070–00005.pdf (accessed June 20, 2009). Rubin argues that Evan might have had a seizure disorder known as Landau-Kleffner syndrome, which is often misdiagnosed as autism. The disorder is described on the website of the National Institute of Neurological Disorders and Stroke, www.ninds.nih.gov/disorders/landaukleffnersyndrome

  /landaukleffnersyndrome.htm (accessed June 20, 2009).

  More generally, autism is a descriptive term for a set of symptoms that can have many different causes. The spectrum of children diagnosed with autism is broad, ranging from kids who are completely nonverbal and unable to interact with others to people who successfully integrate themselves into society and have highly productive careers and relationships. Moreover, the range of behaviors exhibited in autism varies widely, with some people with the diagnosis showing aggressive antisocial behavior and others exhibiting extreme shyness and passivity. Behavioral therapies can be effective in treating the symptoms of autism for many children, helping them learn to interpret and understand the social behaviors of others or eliminating undesirable behaviors. Yet, like cancer, autism is not a single thing. There can be no single cure for cancer because cancer is not a single disease, and there can be no single cure for autism because autism represents a constellation of neurological and behavioral atypicalities that can manifest themselves in a wide assortment of ways.

  33. Evidence about secretin comes from the following sources: D. Armstrong, “Autism Drug Secretin Fails in Trial,” The Wall Street Journal, January 6, 2004 (online.wsj.com/article/SB107331800361143000.html?); A. D. Sandler, K. A. Sutton, J. DeWeese, M. A. Girardi, V. Sheppard, and J. W. Bodfish, “Lack of Benefit of a Single Dose o
f Synthetic Human Secretin in the Treatment of Autism and Pervasive Developmental Disorder,” New England Journal of Medicine 341 (1999): 1801–1806; and J. Coplan, M. C. Souders, A. E. Mulberg, J. K. Belchic, J. Wray, A. F. Jawad, P. R. Gallagher, R. Mitchell, M. Gerdes, and S. E. Levy, “Children with Autistic Spectrum Disorders. II: Parents Are Unable to Distinguish Secretin from Placebo Under Double-Blind Conditions,” Archives of Disease in Childhood 88 (2003): 737–739. The subject is also discussed extensively by Paul Offit in Autism’s False Prophets.

  34. Recall our example of the perceived link between arthritis pain and the weather. In that case, even when people had all of the necessary numbers to properly calculate the correlation, they did not do so. Instead, they judged the strength of a relationship primarily from the number of cases where the putative cause and the putative effect were both present. In the weather/arthritis case, those were the times when the weather was cold and rainy and pain was higher. In the autism example, those were the cases in which kids were vaccinated and later developed autism. In both cases, people ignored all of the other critical numbers. This reasoning error was discovered nearly fifty years ago: J. Smedslund, “The Concept of Correlation in Adults,” Scandinavian Journal of Psychology 4 (1963): 165–173.