The invisible gorilla


The experiment in which observers were asked to count the number of passes made by one team in a three-a-side passing/space finding exercise, is well known because someone in a gorilla costume strolls into the game, pauses to face the camera, and then strolls off. More than half of those participating in the original experiment, by carefully counting passes, did not notice ‘the gorillia’ at all. They would not believe what they were told by those who did see it until shown the video again, when they were not involved in counting passes. Subsequent reruns of the experiment involving participants who were not aware of the previous ones produced the same results, even in (more so in) large audiences watching a cinema screen. There are number of these awareness/observation type video. Some ask for focus on a particular type of action shown and then ask “Did you spot (some other incident/object/change) taking place? Others just require observation and ask how many changes to a scene you noticed. The following observation/awareness videos range in difficulty from simple/easy to difficult and/or very complex – and then I have added three video clips of passages of play in hockey matches where focus on a particular aspect was asked for – and comment on the effects of a focused search by a video umpire.

The following video is another version of the ‘invisible gorilla’ but there are two changes made to the set up, not many people spot both of them, although one is quite easy to see. Try it.

The following, deliberately ‘corney’ ‘Who done it?’ play has a large number of changes to the stage set-up. So many that it will probably be necessary to make written note of them as the video is watched, so that if they are spotted, they can be recalled. The butler is holding a rolling pin at the start but is then to be seen holding a candlestick; other changes are just as obvious, but some are subtle.

In contrast, this section of a security video has only one incident of note, a pickpocket ‘at work’. The thief is not easy to spot because there is a lot of distraction and the clip is almost three minutes long. It’s somewhat like noticing a well rehearsed and executed third party obstruction during a penalty corner: not all skills are desirable.


The following match incidents led to a question about dangerous play on and the participants in the discussion were so focused on whether or not there was a dangerous play offence that they missed several other offences. (The umpire awarded a goal). Count the missed offences.



This play, from a match between ARG and ENG, led to a video referral by the ARG team, who wanted a penalty corner awarded because of a claimed ball-body contact offence by an ENG player. The video umpire was asked to look for a ball-body contact, similar to observes being asked to count the white team passes in the invisible gorilla ciip, and failed (as did the commentators) to take note of any other offence prior to the claimed contact. (A penalty corner was awarded and the ARG team scored from it. That goal, in the last moments of the match, gave them a draw and secured their place in the World Cup, which they won).



I wrote a blog article about the incident some time ago.

In another blog article I have previously commented that denying a team, against whom a video referral has been requested, opportunity to put in a counterclaim (which would not take a significant amount of time) unfairly ‘slants’ the video referral process in favour of the first team to request a referral, because it is likely to give rise to the kind of blindness to other events that a focused viewing of an incident can produce. In the above example a video umpire, asked to look for a ball-body contact offence, failed to notice what were very obvious obstruction offences (invisible gorillas). I believe the referral process ought to allow counterclaim for incidents that can be looked for by the video umpire at the same time as the initially referred incident (Video umpire are supposed to take other relevant incidents into account when they make a recommendation but they generally fail to do so).

Here is another case of a focused search by a video umpire, this time for a ball-foot contact. What was missed was more difficult to see  in this case than in the ARG v ENG incident above. There is no evidence that the ball hits the foot or leg of the ENG player after it is squeezed upwards between the sticks of the GER player and the ENG player, but then the GER player contests for the ball without trying to present his stick to it, his stick, was trailing behind him as he leaned on, barged, impeded and obstructed the ENG player. (GER were awarded a free ball) The ENG team could not even ask for a referral because such a request would have interfered with the original referral.

Books in which reference is made to the phenomena of the ‘invisible gorillia’ (and many more interesting ideas besides)

Daniel Kahneman     Thinking, Fast and Slow.
Cass R Sunstein       Simpler, The future of Government.

(Contains good chapters on simplification of rules and also on looking back at previous regulation to see if it still (or ever) fulfilled the intentions of the legislators after they enacted it.


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