khoji parkPsychology · USA · 1999
The Gorilla Everyone Was Looking Past
The instructions had an unexpected cost.
Read in slides1. Count the passes
Participants watched a video containing people passing basketballs. Their assigned task directed attention toward counting selected passes. The scene also contained something the task did not mention. Seeing the screen was not the same as noticing everything.
The instructions had an unexpected cost.
2. The task has a cost
Counting selected passes gave viewers a reason to direct their attention toward particular people and movements. That was an active task, not a request to watch every part of the scene equally. The unexpected figure therefore tested something about attention while it was already occupied, rather than simply measuring whether a gorilla was visible on a screen.
Looking carefully in one direction could hide another.
3. Another visitor
A person in a gorilla costume entered the filmed scene. The appearance was recorded rather than imagined by a participant. It occurred while viewers concentrated on their counting task. The researchers could ask afterward what people had actually noticed.
The surprise was hiding in plain sight.
4. The missing report
Many viewers failed to report the unexpected figure. Their attention had been occupied by the instructed activity. Failure to notice did not mean the video lacked the gorilla. The difference lay between available information and conscious awareness.
The camera had seen more than they had.
5. Check the footage
Rewatching allowed viewers to inspect the unexpected event directly. The second viewing changed what they were looking for. That made the gorilla much easier to notice afterward. Hindsight could make the original omission seem almost impossible.
Knowing the surprise changes the test.
6. The second viewing is a different experience
Once someone knows what to look for, returning to the video changes the task. The figure can seem impossible to miss precisely because attention is no longer organized around the original instruction. That difference explains why watching again is striking without proving that the first group of viewers had been careless or incapable of seeing.
The surprise had rewritten the instructions.
7. What it means
The experiment became a striking example of inattentional blindness. It showed a limitation under particular viewing and task conditions. It did not establish that people never notice unexpected events. The useful lesson is to test confidence against evidence.
Being sure is not the same as seeing.