Inattentional blindness

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Inattentional blindness is a common but under-estimated phenomenon in human sense-making - a lack of attention or a 'blind spot' to unexpected information. It is a psychological lack of attention that is not associated with any vision defects or deficits, and even experts are subject to it, as in the often-quoted gorilla study.

In a famous experiment, radiologists were asked to spot anomalies in a batch of X-Rays, but 83% failed to see a picture of a gorilla, 48 times the size of a cancer nodule, which was in plain sight on the final X-Ray... and the 17% who do see it came to believe they were wrong when they talked to the 83% who didn't. See this Clip: Dave Snowden on Inattentional Blindness

Why does inattentional blindness happen?

Inattentional blindness is a cognitive heuristic - not a cognitive bias, because if you look at the various cognitive biases, they have all evolved. At the species level, cognitive biases reduce the energy cost of decision making, meaning they are a part of our evolution.

The most you scan available data before making a decision is 3-5% if you are really focused. That rapid scan then triggers a series of cognitive, mental, and social memories that influence your next possible actions.

Relevance to anthro-complexity & Application

Dave Snowden often highlights inattentional blindness as both a warning, and one example of the use of science to gain insight into what is and is not possible in anthro-complexity.

One applicable lesson from these experiments is that someone always sees the Gorilla, but as people with a particular perspective start to discuss a situation they tend to converge into a dominant view, or conflicted views in which small differences that could be vital are readily lost. The true insight from the 17% is lost.

We cannot get rid of cognitive biases/heuristics, we must work with them. You can’t train people not to make this error, so you have to build systems that make the 17% visible to leaders before they conform to the majority belief.

Examples, papers and research

"We like to think that we would notice the occurrence of an unexpected yet salient event in our world. However, we know that people often miss such events if they are engaged in a different task, a phenomenon known as “inattentional blindness.” Still, these demonstrations typically involve naïve observers engaged in an unfamiliar task. What about expert searchers who have spent years honing their ability to detect small abnormalities in specific types of image? We asked 24 radiologists to perform a familiar lung nodule detection task. A gorilla, 48 times larger than the average nodule, was inserted in the last case. 83% of radiologists did not see the gorilla. Eye-tracking revealed that the majority of those who missed the gorilla looked directly at the location of the gorilla. Even expert searchers, operating in their domain of expertise, are vulnerable to inattentional blindness." - Drew, Võ & Wolfe (2013): The Invisible Gorilla Strikes Again - Sustained Inattentional Blindness in Expert Observers. Psychological science, Sep 2013; 24(9): 1848–1853

Another common example of this experiment also involves a gorilla - participants are asked to watch a short video (for example in which six people - three in white shirts and three in black shirts - pass a basketball. While they watch, participants are asked to keep a silent count of the number of passes made by the people in white shirts. At some point, a gorilla strolls into the middle of the action, faces the camera and thumps its chest, and then leaves, spending nine seconds on screen. Almost everyone assumes they would notice the gorilla - however this experiment finds that up to half of the people who watch the video and counted the passes miss the gorilla entirely.


  1. Drew, Võ & Wolfe (2013): The Invisible Gorilla Strikes Again - Sustained Inattentional Blindness in Expert Observers. Psychological science, Sep 2013; 24(9): 1848–1853
  2. Simons DJ, Chabris CF. Gorillas in our midst: sustained inattentional blindness for dynamic events. Perception. 1999;28(9):1059–1074. [PubMed] [Google Scholar]
  3. BLOG: Bias or heuristic? Dave Snowden, August 30, 2019