Octopuses Fall for the Rubber Hand Illusion

Amazing!

Photo by Diane Picchiottino on Unsplash

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Here’s something wild: Octopuses fall for the rubber hand illusion, a psychological effect previously only documented in humans and a few other mammals. This surprising finding hints at deeper similarities between our minds and theirs, despite half a billion years of separate evolution.

In the standard human version of the illusion, a fake hand is placed in front of a participant while their real hand is hidden behind a screen. Both the fake hand and the real hand are then stroked in synchrony. Before long, the brain “adopts” the fake hand as part of the body. It adopts it so completely, in fact, that when the fake hand is threatened, the participant involuntarily flinches.

The illusion is a powerful - and often hilarious - demonstration of how the brain stitches together information from multiple senses to construct the feeling of body ownership: the intuitive, usually unnoticed sense that your body parts belong to you.

Here’s a video showing the standard effect:

Until recently, the rubber hand illusion had only been observed in mammals, including humans, monkeys, and rodents. Now, however, researchers have demonstrated the effect in a much more distantly related animal: the octopus.

Here’s the proof:

And here’s a longer video with some background and more details about the research:

That octopuses are susceptible to the rubber hand illusion is deeply fascinating. The last common ancestor of humans and octopuses lived more than half a billion years ago. It was probably a simple worm-like creature with barely a hint of a brain. This means that our cognitive abilities and theirs evolved almost entirely independently. And just as we might expect given that evolutionary backstory, octopuses have a radically different brain architecture from ours, not to mention a radically different body plan. Nonetheless, they and we share a fundamental psychological building block: the sense of body ownership.

The fact that this building block evolved independently in two such different species suggests that body ownership may be more common in the animal kingdom than we might have assumed, and that it may be a crucial component of consciousness, at least for intelligent creatures. It also hints that, as different as we are from octopuses, their minds aren’t entirely alien to ours.

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