Saturday, July 29, 2017

Why the Muller-Lyer Illusion Disappears in the Future

Familiar with the Muller-Lyer Illusion?  Well, if not, here it is.  Many people perceive the line on the right to be longer than the one on the left.  Up to 20% longer, and it’s not.  It’s the same length.  Do we know what causes this illusion?  Well, maybe. 

I won’t bore you with the details (well, not all of them anyway), but one popular theory is that we ‘learn’ it from our experience in right-angle environments, the so-called ‘carpentered worlds.’  The line on the right looks like an inside corner – like the corner of a room, if you’re sitting in one.  The line on the left, an outside corner.  Since the inside corner is receding in distance, we perceive it to be longer than the outside corner that is sticking out toward you, even if physically (e.g., by a ruler) they are the same length.

Got that?  Amazing what our brains do, even if they fool us once and a while…or more.  But, the question for today:  what happens to the Muller-Lyer in the future?  I have my guess – it disappears.

It’s not that we stop carpentering our worlds in right angles.  I doubt that.  But our experience with depth becomes stunted.  Our friends and family don’t live down the block.  They live on our 2D phone and tablet surfaces.  Even film and game makers give up on 3D glasses and head-mounted displays.  The body’s sense that we aren't moving never lines up with 3D when it says we are.  And besides, who needs 3D when our heroes save the world from an alien invasion using their 2D, battle-command interface?  A 3D film to show a 2D screen…huh?

But what about just plain getting around in the future?  Between virtual work and every retailer dropping orders into your drone-delivery chute, it’s rare.  And when we do go out, the first thing we do in our self-driving car is turn all the windows into 2D displays.  Wouldn’t want to miss the latest 2D video of a dog chasing its tail.

So, I’m telling you this as a favor.  You see, the next time I’m in a fender-bender or even have a disagreement with a light pole, I’m telling the officer, “Sorry, but it’s not my fault.  See, I’m just ahead of my time in losing my depth perception.”

Image by Twincinema at sv.wikipedia [GFDL ( or CC-BY-SA-3.0 (], from Wikimedia Commons