The invisible gorilla: what inattentional blindness tells us about our work
In 1999, two Harvard researchers showed that people can fail to see a gorilla walking right through the middle of a scene. This now-famous experiment sheds light on a mechanism that traps competent professionals every day.
In brief
- About one person in two fails to see the gorilla when busy counting passes.
- It is not an eyesight problem: when attention is taken, the brain filters out what it does not expect.
- Knowing about the trap does not protect you: you simply miss something else.
- The best defence is collective: a colleague whose role is to look elsewhere.
The experiment
Daniel Simons and Christopher Chabris filmed two teams of three players, one in white and one in black, passing basketballs. They asked viewers to count the passes of the white team. Halfway through, a person in a gorilla suit crosses the scene, stops facing the camera, thumps their chest and leaves. They are on screen for 9 seconds.
Result: about one viewer in two does not see them.
What it reveals
This phenomenon is called inattentional blindness. When our attention is taken up by a demanding task, the brain does not process everything that reaches the retina: it filters out what does not match what it is looking for. We feel we see everything, while we perceive only part of the scene.
What if you know about the trap?
In 2010, Daniel Simons repeated the experiment with two extra changes: the background curtain changes colour and a player leaves the frame. Those who already knew the video all saw the gorilla, but very few noticed the two other changes.
At work, where are our gorillas?
A driver focused on a phone call, a surgeon absorbed by a technical difficulty, a manager engrossed in a dashboard: in each case, the essential may lie right next to what they are looking at. Accident reports in aviation, rail and healthcare often describe this mechanism.
- A meeting where everyone follows the agenda without seeing that the main problem is not on it.
- A project steered by its indicators while the client is leaving.
- A task repeated a hundred times, where the unusual detail is no longer noticed.
How to protect yourself
Willpower alone is not enough: you cannot decide to see what you do not perceive. The defences are mostly collective.
- Share roles: while one person focuses on the task, another keeps the big picture.
- Protect critical phases from interruptions, like pilots below 10,000 feet.
- Encourage everyone to flag what seems unusual, even without certainty.
FAQ
Frequently asked questions
Where can I see the original video?
It is published by Daniel Simons on YouTube under the title “selective attention test”.
Are experts less prone to inattentional blindness?
No. It is part of the brain’s normal functioning. Expertise helps you know where to look, but not to see everything.
Sources
- Overview of the Simons and Chabris study (PMC)
- Time, the follow-up experiment in 2010
- “Selective attention test” video, Daniel Simons
