Plants Experience Optical Illusions, Too

You know that the two lines are the same length, or the image isn’t moving, etc., but you can’t force your brain to process the information that way, no matter how hard you try. Per a new study published in Proceedings of the National Academy of Sciences, even organisms with no brains, like plants, can get fooled by optical illusions. According to a team of botanists from Tel Aviv University who uncovered this odd phenomenon, the secret is in the way the plants receive information from light.

Your light receptors are located on the front of your face, but plants have light receptors all over their bodies (and primarily on their stems). It’s a more distributed sensory system. Read more: “12 Mind-Bending Perceptual Illusions” To find out how plants interpret these signals, the team turned to the most iconic light-seeker: the sunflower.

In a series of experiments they subjected sunflowers to light sources of varying intensities and from different directions. In the first experiment, they used a single light source, cranking up the intensity. As expected, the plants bent toward the light, although the team ran into diminishing returns.

Next, they used two opposing light sources of differing intensities. While the plant bent toward the brighter light, the angle of its bend didn’t seem to vary linearly with the difference in brightness. Things got a little crazy when the team confounded the sunflowers with two opposing light sources of identical intensity but added a third, weaker source perpendicular to the two.

Remarkably, the plant bent toward the weaker light. In other words, the two brighter lights seemed to cancel each other out (at least in the sunflower’s “mind”). The team says the signal from light gets transduced in a non-linear way (i.e., doubling the intensity doesn’t double the signal).

To the extent the plant is “doing math,” it’s adding up the direction of the signals after they’ve been transduced rather than the intensity of the light input. With two opposing bright light sources, the vectors cancel out, and that’s what leads to the apparent “optical illusion.” And because this kind of processing is intrinsic to the distributed nature of the sensory system, the implications of the findings could be far-reaching. Subscribe to our free newsletter.