Inattentional blindness is the failure to notice something fully visible because your attention is taken up by something else. It has nothing to do with eyesight: people often look directly at the thing they miss. In the best-known demonstration, almost half of the viewers counting basketball passes did not see an unexpected event walk through the middle of the scene. It is a normal side effect of focused attention, not a sign of low intelligence.

The invisible gorilla experiment

In 1999 Daniel Simons and Christopher Chabris, then at Harvard, made four 75-second videos of two teams, one in white shirts and one in black, passing basketballs. Viewers were asked to count the passes made by one team. Partway through, an unexpected event lasted 5 seconds: either a woman carrying an open umbrella walked across the scene, or a person in a full gorilla suit did.

  • Across all 192 viewers, 46% did not notice the unexpected event at all, even when asked directly afterwards.
  • The gorilla was harder to see than the umbrella woman: 44% noticed the gorilla overall, against 65% for the umbrella woman.
  • What you attend to matters. Among viewers counting the white team’s passes, only 27% saw the black gorilla; among those counting the black team, 58% did.
  • Harder tasks cause more misses. Viewers who kept two separate counts noticed the event less often (45%) than those who kept one (64%).

The study built on an older one. In 1975 Ulric Neisser and Robert Becklen showed that people following one of two overlaid games often missed odd events in the other. The term inattentional blindness itself comes from Arien Mack and Irvin Rock, whose 1998 book argued that there is no conscious perception without attention.

Why we miss what is in front of us

Attention is a filter. To follow the passes, your brain boosts what looks like the team you are tracking and suppresses what looks like the team you are ignoring. That is attention doing its job, and the research points to four things that decide whether an unexpected object gets through:

  • Similarity to what you are tracking. In experiments with moving shapes, the more an unexpected object resembled the attended items, and the more it differed from the ignored ones, the more likely people were to notice it. That is why the black gorilla was easier to see for people tracking the black team.
  • How hard the main task is. More mental load leaves less spare capacity. Our page on cognitive load explains why that capacity is so limited.
  • Expectation. A gorilla does not belong in a basketball drill, so nothing primes you to look for it.
  • Looking is not seeing. Eye-tracking studies show that many people who miss the unexpected object look right at it — in one study of children, for about one second, as long as those who did report it.

Inattentional blindness vs change blindness

The two are related but not the same, and they are often confused.

  • Inattentional blindness is missing an unexpected object or event that is present while your attention is elsewhere — the gorilla.
  • Change blindness is failing to notice that something has changed from one view to the next. In a 1998 field study by Simons and Daniel Levin, an experimenter asked a passer-by for directions; two people carrying a door walked between them, and the experimenter was swapped for a different person. Many passers-by carried on giving directions without noticing that they were talking to someone new.

A common summary says change blindness is about slow or gradual changes. That is too narrow: the classic demonstrations use large, sudden changes that happen during an interruption — a blink, a camera cut, a door. What both effects share is that we keep far less detail from moment to moment than it feels as if we do.

Outside the laboratory

  • Experts in their own field. Trafton Drew and colleagues asked 24 radiologists to search chest scans for lung nodules and inserted a gorilla 48 times the size of an average nodule into the last case. 83% did not see it, and eye tracking showed that most who missed it looked directly at its location.
  • A fight beside the road. In a re-creation of a real Boston police case, people jogging after a target ran past a staged fight while counting how often the runner touched his head. Only 35% noticed the fight at night and 56% in daylight, and a harder counting task lowered noticing further.
  • Phones while walking. In a 2010 study, people walking while talking on a phone were less likely to notice a unicyclist in a clown costume than people walking alone, listening to music or walking in pairs.
  • Missing still has a cost. In experiments at the University of Padua, 97 of 165 observers missed an unexpected moving object, and the object lowered their accuracy on the main task only when they did not consciously see it.

Is it related to intelligence?

Weakly at most. In a 2011 study, 58% of viewers noticed the gorilla, and among those who counted accurately, people with higher working memory capacity noticed it more often (67%) than those with lower capacity (36%). But a larger 2015 study by Carina Kreitz, Philip Furley, Daniel Memmert and Simons tested several kinds of task and found that working memory, attention breadth and other cognitive measures mostly did not predict noticing; the one link they found was fairly weak, and people who noticed in one task were only weakly more likely to notice in another. The authors concluded that noticing depends more on chance processes common to everyone than on stable individual differences.

So missing the gorilla says nothing useful about your IQ, and the gorilla video is not an intelligence test. Intelligence tests measure reasoning on problems you are asked to solve; inattentional blindness is about what reaches awareness when you are not looking for it. The closest link is through executive function, the control processes that hold a goal in mind — the same processes that make the filter work.

Can you reduce it?

  • Knowing about it is not enough. People who knew the gorilla video spotted the gorilla in a new version, but were slightly less likely than newcomers to notice two other unexpected changes in it.
  • Domain expertise helps a little. Basketball experts noticed an unexpected object in a basketball task more often than novices, but the radiologists show that expertise does not make you immune.
  • Lower the load. Fewer simultaneous tasks leave more spare attention: no phone while driving or crossing a road, one task at a time when errors matter.
  • Build in a second look. Checklists and a deliberate final scan for “anything else” are how safety-critical professions work around a limit no one can simply train away.

For how attention spreads across a busy screen, and why action games train it only narrowly, see do video games make you smarter?

Trust and scope notes

This page summarises published research for general information, with the figures taken from the studies listed below. Nothing here is medical or safety advice. The IQ Revealed test is an online reasoning test of 40 original items for adults aged 18 and over; it is not a clinical assessment and it does not measure attention or perception, and our guide to how IQ tests work explains what an online test can and cannot tell you.

IQ Revealed is not affiliated with, endorsed by or connected to Daniel Simons, Christopher Chabris, the universities, journals, publishers or researchers named on this page, or any owner of the “invisible gorilla” video. Names are used only to identify the research being described.