Bat­ter­ies not re­quired

Popular Science - - HEAD TRIP - by Ni­cole Wets­man

ROLL THIS MAG­A­ZINE INTO A TUBE. NOW, keep­ing both eyes open, look through it with one eye. Com­pared with the plain view, the tube-fil­tered scene will seem brighter, as if lit by a flash­light. This makeshift torch will even make tex­tures and pat­terns pop.

No one has a de­fin­i­tive ex­pla­na­tion for this false il­lu­mi­na­tion. Neu­ro­sci­en­tists’ best guess is that it has some­thing to do with the way our brain in­ter­prets con­trast. Within a tubu­lar sight, the cir­cu­lar bor­der ap­pears darker than the en­vi­ron­ment within it. This trig­gers some­thing called the bright­ness en­hance­ment ef­fect, in which your per­cep­tion of an ob­ject’s lu­mi­nos­ity changes when you view it along­side some­thing else. In fact, re­searchers found that the in­te­rior view ap­pears nearly twice as bright as what’s out­side it.

This trick isn’t just a fun thing to do with Pop­u­lar Sci­ence af­ter you’ve read it cover to cover; it has prac­ti­cal ap­pli­ca­tions too. Ra­di­ol­o­gists some­times use the il­lu­sion’s power to make out faint yet po­ten­tially im­por­tant de­tails on scans, like a slight bone frac­ture or a tiny tu­mor. Even if the light is all in our head, in a pinch, it still works.

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