Viral: Train Track Optical Illusion Fries Internet Brains

A UK dad was playing with his son’s toy train track when he noticed something unusual. The video he posted online has since fried a few brains by confused viewers. There is, however, a simple explanation.

Train Track Optical Illusion

The video, posted by Marc Blank-Settle on April 6, 2016, shows two train tracks placed next to each other. The top track appears to be about an inch shorter than the bottom track. When the man stacks the two tracks, however, they appear to be the same size. He then un-stacks and re-stacks them with the same result each time.

My toddler’s train track is freaking me out right now. What is going on here?! pic.twitter.com/9o8bVWF5KO

— marc blank-settle (@MarcSettle) April 6, 2016

Despite the appearance of one track being longer in the un-stacked configuration, the tracks are actually the same size, and this phenomenon was first described in 1889 as the “Jastrow Illusion.”

Jastrow Illusion

American psychologist Joseph Jastrow described the illusion in 1889, noting that when viewing two curved shapes next to each other, one can look larger than the other. According to the New World Encyclopedia:

Scientists are not yet certain what causes one figure in the Jastrow illusion to appear larger than the other. Similar effects have been noted by a number of researchers using a variety of geometric shapes, including trapezia, parallelograms, and lozenges.

The fact that the shorter side of one figure is next to the longer side of the other somehow tricks the brain into perceiving one shape as longer and the other as shorter, although it is unclear exactly why this is so.

Aligning the two tracks in the manner above enhances the illusion. In the video above, when the tracks are placed side by side, the dad aligned the bottom left corner of the top track with the top left corner of the bottom track. Had he aligned them centered with each other, the tracks would have appeared more similarly sized.

As the graphic above displays, the alignment performed in the video gives the appearance of a longer bottom track. Centering the tracks – as shown in the bottom example – reveals that the tracks are in fact the same length.