Octopi Illusions

Here’s an interesting trick: If an individual hides one hand and replaces it with a realistic rubber one, and both the real and the fake hand are touched simultaneously, most will feel touch in the fake hand and start to believe it is actually part of their body. 

That’s true in humans but also in octopi. 

That’s the conclusion of a new study, where researchers say that plainbody night octopi (Callistoctopus aspilosomatis) have a sense of body ownership and a certain awareness of their limbs’ position and movement in space. 

Previous studies have found that mice and monkeys are also fooled by the illusion but this is the first recorded instance of a non-mammal creature falling for the trick, according to Science Magazine. 

To carry out the study, researchers placed one octopus in a tank. Then, they put a fake arm made of a soft gel attached to an opaque partition over one of the octopus’s real arms, so the animal could see the fake limb but not the real one, according to Phys.org. 

Scientists stroked both the real and fake with plastic calipers at the same time for about eight seconds. Then, they squeezed only the dummy arm with a pair of tweezers. The octopus reacted defensively, as if it had really felt the tweezers’ pinch. 

The team repeated the test multiple times with five different octopi, and all exhibited defensive responses, such as attempting to flee, changing color or retracting their arms, all responses scientists would expect from the creatures if the real limb had been pinched. 

The illusion disappeared in experiments where the real and fake limbs were not stroked simultaneously, were not stroked at all or the fake arm didn’t match the real one, explained the Smithsonian Magazine. 

“These findings in the octopus, which has a complex nervous system that has developed independently of vertebrates, may be an important model for studying the evolution of the sense of body ownership,” wrote the researchers. 

The results might also help the development of better robots and artificial intelligence systems or be useful to doctors researching neurological disorders in humans.