Ignoring the obvious – invisible gorillas and sex-change tourists

If you haven’t seen the ignoble-winning work of Daniel Simons, take a look at this video. Concentrate on counting the number of times the people wearing white pass the ball. Try it on a friend. Pressure them to concentrate on the white team by re-inforcing how hard the task is and the necessity of counting all the passes but not the bounces. If they don’t know about the gorilla that walks through the basketball game, thumping it’s chest, chances are they won’t see it.

How can someone miss a large gorilla???? Obviously your eyes must “see” it, but it is never brought to your conscious attention. You only really consciously notice something if you are trying to see it, or it is new, interesting or dangerous. In the case of this video, you concentrate on the people in white, ignoring anything black. If you concentrate hard enough, you won’t see the gorilla. It’s part of the attentional bottleneck theory – that you only have finite resources and thus if you are really attending to something, you will not be able to process anything else.

And it’s not just videos. The same research team tested students at a university by having a “tourist” ask them directions on a map. Whilst giving directions, a couple of people carrying a door walked between the tourist and the person asked for directions. Whilst passing, the tourist changed places with one of the door carriers – thus leaving a different “tourist” to complete the discussion. Around 50% of people asked did not notice the change despite enormous differences in accent, clothing and appearance.

It seems ridiculous that we could evolve a sensory system that can’t see something like a gorilla, but it really isn’t. It’s a useful adaptation. Imagine walking into a room and being instantly aware of all the furniture, the paint, the title of every book etc. It would be overwhelming and pointless. Instead the sensory system has evolved to see only the things of importance in the room – the open champagne, the strawberries and the cute blonde (for example).

But ignoring too much is also dangerous – what if the gorilla was armed? Thus attention is a careful balance. Notice too much and you may overwhelm the senses – making it hard to see a lurking predator. Notice too little and the predator could be upon you in seconds.


Simons, D. J., & Rensink, R. A. (2005). Change blindness: Past, present, and future. Trends in Cognitive Sciences, 9(1), 16-20.

Simons, D. J., & Chabris, C. F. (1999). Gorillas in our midst: Sustained inattentional blindness for dynamic events. Perception, 28, 1059-1074.

Simons, D.J., & Levin, D.T. (1998). Failure to detect changes to people during a real-world interaction. Psychonomic Bulletin and Review, 5, 644-649



Filed under Curious Science, Science

4 responses to “Ignoring the obvious – invisible gorillas and sex-change tourists

  1. It’s funny you should mention weapons (though my wife would, I’m sure, not hesitate to mention the similarities between me & an armed gorilla) …

    One of the interesting things that self defense trainers have noticed is that in stressful situations, people often don’t notice weapons, but focus entirely on body language (and especially the eyes).

    E.g. in one scenario, trainee policemen were given a series of open-ended role-playing exercises. Most were simple requests for directions, parking tickets, etc. In one, however, the other participant (one of the trainers) would produce a rubber knife, brandish it, shout “I’m gonna cut you up, pig!” and then attack the trainee.

    In most cases, the trainees reported not noticing the knife, despite the brandishing & verbal threats, until feeling a strike. In a few cases, the trainees never noticed the knife, and had to be shown a video of the interaction before they’d believe there was a weapon involved.

    Likewise, members of hostage rescue teams have to be trained to consciously look for weapons, rather than staring at the eyes of people in a room they’ve just breached.

  2. Wow. This experiment is one of my favorites, and has so many many implications. If something doesn’t fit into out model, we don’t see it? Maybe things like UFOs and sea monsters are “real” but most people don’t see them because of this tendency? How many gorillas do we not see?

    This is useful information. I once used a public bathroom other people were afraid to use cause two peeps were having a knife fight in it. I knew darn well they wouldn’t even see me, and they didn’t.


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