Simons and Chabris inattentional blindness 1999
Observers counting passes by one team often failed to notice a person in a gorilla suit or an umbrella-carrying woman crossing the scene.
Main paper: Simons, D. J., & Chabris, C. F. (1999). Gorillas in our midst: Sustained inattentional blindness for dynamic events. Perception, 28(9), 1059–1074. https://doi.org/10.1068/p281059
The question
Can people miss a fully visible, unexpected object when attention is on something else?
Design: experiment
The researchers set the conditions and compare outcomes between or within groups. Each profile says whether participants were randomly assigned.
Different groups of observers saw different versions of the video. This profile does not state how observers were assigned or give counts.
Count one team's passes
- Watch two teams pass balls
- Unexpected figure crosses the scene
Result reportedMany do not notice it
Variations
- Change team similarity
- Change task difficulty
Result reportedNoticing rate changes
Original diagram drawn for this site from the descriptions in the sources. It is a simplified summary, not a figure from the paper.
Procedure
Observers watched a video of two teams, one in white shirts and one in black, passing basketballs. They counted passes by one team. Partway through, an unexpected event crossed the scene: a woman with an umbrella or a person in a gorilla suit. After the video, observers were asked whether they had noticed anything unusual.
The authors varied the video, for example by making the action more or less transparent and by changing which team observers counted, so the unexpected object was more or less similar to the attended team.
Findings
A large share of observers did not report the unexpected event. The textbook account of the gorilla version says nearly half of viewers missed it although it was on screen for several seconds. Noticing depended on the version of the task, including how similar the object was to the team observers were tracking.
Interpretation
The authors concluded that noticing depends on attention and expectations, not only on what is in view. Observers who missed the event were often accurate at counting, which indicates that the lapse was not general carelessness.
Limits on what it shows
- The video is staged and the counting task is demanding, so how often real-world events are missed is not shown.
- Not noticing is measured by later report, so some observers may have noticed and forgotten.
- The gorilla video most people know is one version of a larger set of conditions, and it should not be read as a general rule about everyday life.
Ethics
A short video task carries little risk. The result can feel surprising, so a debriefing that explains why missing the object is common helps participants.
Replication and reassessment
The authors varied features of the task, so a single gorilla demonstration is only one example. Task difficulty and the unexpected object’s similarity to attended objects affected detection. Missing an event while accurately counting passes is compatible with selective attention.
Think it through. An original practice question written for this site.
If someone misses the gorilla but counted the passes correctly, what does that say about a claim that they were simply not paying attention?
Show a way to reason about it
Accurate counting shows they were paying attention to the task. The failure to notice happened because attention was directed there, so the lapse reflects where attention went, not how much there was.
Nothing you think or select here is recorded.
Textbook connection
Covered in this sectionOpenStax Psychology 2e, 5.1 Sensation versus Perception
Section describes the pass-counting task and inattentional blindness.
Sources and access scope
Each label says how much of the source was opened while preparing this profile. An unopened source is listed so the claim can be checked, not because it was read.
- Simons, D. J., & Chabris, C. F. (1999). Gorillas in our midst: Sustained inattentional blindness for dynamic events. Perception, 28(9), 1059–1074. https://doi.org/10.1068/p281059Consulted sourceOriginal researchAbstract inspected
Abstract inspected for the effects of similarity and monitoring difficulty. The full article was not inspected; the textbook supplies the familiar gorilla demonstration.
- Spielman, R. M., Jenkins, W. J., & Lovett, M. D. (2020). Psychology 2e. OpenStax. https://openstax.org/books/psychology-2e/pages/5-1-sensation-versus-perceptionTextbook contextSelected textbook passages inspected
Textbook context. The section describes the counting task and the gorilla result in general terms.