A Necker cube is bi-stable figure, meaning that it can be perceived as two different three-dimensional objects, depending on how you look at it:
Cube A is ambiguous — the true Necker cube. Cube B and cube C show the two ways you can perceive the Necker cube: either the bottom of the cube is in front, or the top is in front. What’s interesting about figures such as the Necker cube is that once you’re aware of its bi-stable nature, it’s impossible to see it only one way. Don’t believe me? Then take this challenge. Play the movie below (it lasts for two minutes). The figure will flash every couple of seconds, but otherwise there are no tricks involved — the identical, ambiguous figure is portrayed the whole time.
You can choose whether you’d like to see it as bottom-in-front (like cube B) or top-in-front (like cube A). But you won’t be able to maintain that perception for the entire time you watch. Just make sure you’re perceiving it as a cube, and not just a two-dimensional group of lines.
Stop the movie once you see the reverse, and let us know how long you lasted in this poll:
Researchers have found even when they’re trying to avoid a reversal, people switch at least once every fifteen seconds. The flashing makes it more difficult to avoid reversing, but even non-flashing objects are always reversed. People who say they never reversed are lying (with one possible exception, which I’ll get to later).
Jürgen Kornmeier, Christine Maira Hein, and Michael Bach showed ten volunteers movies similar to the one I presented above, asking them to press a key every time they saw a reversal. (This turned out to be agonizingly difficult after repeated trials, so eventually the viewers were given breaks and asked to return several weeks later to complete the experiment). The viewers were sometimes told to try to keep the image stable, sometimes to just relax and let it reverse as often as it would naturally, and sometimes to try to reverse as often as possible. Here are the results:
The three strategies resulted in three different results: Viewers were able to reverse the cube significantly less often when they were consciously trying to do so compared to when they just relaxed and let it happen. And deliberately trying to reverse resulted in more reversals.
But clearly reversal isn’t completely under our control: we can never stop reversing entirely, and changing to a flashing display led to significantly more reversals, whether viewers were trying to reverse the cube or not. Flashing the cube had a similar effect on every strategy the viewers used to reverse (or prevent reversals).
There may be one exception to the rule that everyone reverses Necker cubes: One study found that Buddhist monks were able to prolong the stability of an ambiguous figure after meditation. But it’s unclear whether even they would be able to manage this indefinitely.
J KORNMEIER, C HEIN, M BACH (2008). Multistable perception: When bottom-up and top-down coincide Brain and Cognition DOI: 10.1016/j.bandc.2008.06.005