07-23-2025

Octopuses are tricked by the 'rubber hand illusion' like humans, suggesting self-awareness

Earth.com staff writer

Imagine reaching for a cup and feeling as though your hand is moving, only to discover it’s not your hand, but a rubber replica being touched in sync with your real, hidden hand. You still react, convinced the fake rubber hand is yours.

Humans fall for this trick every time, and now we now know that octopuses fall for it, too.

In a surprising study, scientists found that these famously alien-like creatures respond just like humans and other mammals when exposed to this sensory illusion.

Their brains, which are vastly different from ours, still make the same mistake. That suggests a deeper commonality in how ownership of bodies is understood by living minds, regardless of how those minds are built.

What the rubber hand trick shows

The rubber hand illusion was first demonstrated in the 1990s. It involves hiding a person’s real hand behind a screen while a fake rubber hand is placed in full view.

When both hands, real and fake, are stroked simultaneously, the brain starts to link the sensations to the fake hand.

Eventually, the person begins to feel ownership of the rubber hand. Pinch the fake one, and the person flinches. Later studies showed that mice were also fooled by the same trick.

The illusion appeared to tap into a widespread brain function that integrates vision, touch, and body awareness into a unified sense of self. But these animals are mammals, like us.

Their brains share much of our architecture. So scientists naturally asked: What about creatures with entirely different neural setups?

How the octopus brain sees its arms

Octopuses are unlike any other creature on Earth. They have nine brains – one main brain and eight smaller ones, one in each arm. Their nervous systems are highly distributed.

An arm can even move independently after being severed. This structure makes their cognition incredibly difficult to compare to ours. Still, they’re known for cleverness, problem-solving, and even mischief.

So when researchers at the University of the Ryukyus in Okinawa, Japan, set out to test whether octopuses would fall for the rubber hand illusion, the scientific community took notice.

If octopuses could be fooled too, it would mean their brains also create a kind of body image, despite the alien wiring.

That would change how we understand intelligence and body awareness across the animal kingdom.

How the fake arm test fooled octopuses

Sumire Kawashima and Yuzuru Ikeda led the study. They worked with six captive, plain-body octopuses (Callistoctopus aspilosomatis).

Each was placed in a tank with an opaque barrier that blocked its view of one arm. Above this hidden arm, a fake octopus arm made of soft gel was placed. The fake arm looked natural and matched the posture of the real one.

A researcher then stroked both arms, the real hidden one and the fake, visible one, at the same time using plastic calipers.

This synchronized stimulation mimicked the human rubber hand illusion. After eight seconds, they pinched the fake arm with tweezers and observed how the octopus responded.

Octopus reaction to fake arm

The reactions were clear and strong. All six octopuses showed defense responses when the fake arm was pinched.

Some changed color, some pulled back their arms, and others tried to escape. These are all natural behaviors that octopuses use when they sense danger.

But when researchers removed the synchronized stroking, or when the fake arm did not match the posture of the real one, the illusion failed. No defense responses occurred. The octopus no longer saw the fake arm as part of it’s own body.

This result was striking. The illusion worked only when the visual and tactile cues matched perfectly.

That means the octopus brain was combining multiple types of information to build a sense of its own body. In that moment, the fake arm became real.

What the scientists learned

For co-author Yuzuru Ikeda, the study offers a glimpse into both the power and limits of brain function.

“The illusion would suggest the ability of octopuses to anticipate and predict, which is advantageous for survival,” he said.

“On the other hand, this ability arises as a side effect of a mistake or conflict of processing in the brain and is also a flaw.”

In other words, this illusion is a double-edged sword. The same brain function that helps predict and react to the world can also misfire. And yet, this mistake reveals how sophisticated the octopus’s sense of self may be.

Sumire Kawashima believes the findings push octopuses into an even more important role in neuroscience.

“Our findings suggest the octopus may be an important model for studying the evolution of the sense of body ownership,” she said.

This places octopuses alongside mammals as useful subjects for understanding consciousness and cognition.

More insights on animal consciousness

Peter Godfrey-Smith, a philosopher of science at the University of Sydney, has long studied octopus minds. He was surprised by the results.

“It suggests that octopuses have quite a rich body image,” he said. “I am struck by the fact that the ‘posture incongruence’ condition worked as it did: the octopuses did not see the rubber arm as their own in that case, despite the stroking.”

His reaction highlights just how unexpected this discovery is. Even subtle mismatches between the real and fake octopus arm broke the illusion.

That level of precision points to a complex internal model of the body, something many did not expect to find in a species so different from ours.

This experiment offers more than just an odd glimpse into animal behavior. It challenges deep assumptions about how minds work.

If both humans and octopuses can be tricked into adopting a fake limb, then perhaps the roots of self-awareness are older and more widespread than we believed.