Cognitive Psychology · Simplified
Change Blindness
Something in this scene keeps changing. It is large, it is not hidden, and you will probably not be able to find it.
With the blank
Find the one thing that changes
The scene below alternates between two versions of itself, with a blank moment in between. Exactly one thing is different. Press the button as soon as you can see what it is.
Before you start. The picture alternates about once a second, which is well below the rate associated with photosensitive seizures, and nothing flashes brightly. If you would rather not have anything change on its own, use Step by hand and move through it one picture at a time. Neither route is timed out.
Which one was it?
The comparison
The blank was doing all the work
Key idea: When something changes in front of you, the change itself produces a signal: a bit of the picture suddenly differs from what was there a moment ago, and that signal pulls your attention straight to it without you having to look for anything. Put a blank moment in between and every part of the picture changes at once, so that signal is swamped and no longer points anywhere. You are left having to compare what is on screen now with what you remember of a second ago, one object at a time, and that is slow. The change was never too small or too subtle. It was never hidden. You simply had no signal telling you where to look.
Two things this does not show. It does not show that you store nothing about a scene: people who miss a change can still describe a great deal of what they saw, and a slow search is time spent attending elsewhere rather than time spent blind. And the two runs here use different scenes on purpose, because running the same scene twice would mean the second search was faster partly because you already knew where to look. That makes this a fairer comparison than the usual classroom demonstration, but it is still one person and two scenes, so treat the two times as an illustration rather than a measurement.
The longer version adds several scenes, a control over what kind of thing changes and where, and a comparison table across every run. It is at Change Blindness in the main collection.