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Cognitive Psychology · Simplified
Inattentional Blindness
A counting task on a crowded display. Take it seriously: the count is the point, and it is harder than it looks.
The counting task
Count the solid down-pointing triangles
The display holds a mix of shapes, some solid and some outlined. Count only the triangles that point downwards and are filled in. There is no time limit, and nothing on the display moves or changes.
Once each. This works properly the first time and not afterwards, so do the count before reading anything else on the page.
Count the solid down-pointing triangles
Both things have to be true: pointing
downwards, and filled in. Ignore every other shape.
Take as long as you like.
Now one question about the same display, before it comes back.
This spoils the demonstration for whoever is at this screen.
The display again
The same display, with everything marked
Nothing has been added or moved. This is the display you were looking at. The shapes you were counting are ringed with a solid line. The five-pointed star, which nobody asked you about, is ringed with a dashed line and is the larger ring.
Key idea: Attention and awareness are related but not the same thing. A demanding task on a crowded display takes up the capacity that reporting an unasked-for object would need, and the object can sit in plain view, fully resolved by the eye, without being reported. Nothing was hidden, nothing was brief, and there was no time limit.
Three cautions. Not reporting is not the same as not seeing: this task cannot separate an object that never reached awareness from one that did and was not remembered a few seconds later, and that distinction is still argued over. The result is a property of the display and the task rather than of you, so a different count on a less crowded array would very likely give a different outcome, and nothing here measures your attention. And you are no longer a naive observer: running it again shows how the design works, not whether you would have missed it.
The longer version adds four deterministic display variants, a table of what each design change alters, and a challenge on which change should matter and why. It is at Inattentional Blindness in the main collection.