Here’s a great way to spend science dollars: see if humans literally find robots sexy. They do sort of, or so conclude Stanford researchers who asked volunteers to touch an anthropomorphic robot in various body parts.

Still from the movie Ex Machina (2015).

Nao is a friendly looking robot with a plastic shell that looks more like a toy then a sexy Ex Machina automaton. What Nao lacks in looks, it makes up for in attitude. The robot directly and bluntly asked volunteers to either point at or touch one of its 13 body parts. “Sometimes I’ll ask you to touch my body and sometimes I’ll ask you to point to my body,” the 2-foot-tall humanoid told them. M’kay?

The hapless students who volunteered for the experiment thought this was some sort of anatomy study.  Jamy Li, a PhD student in Stanford’s Department of Communication and of the lead authors of the study, had something different in mind. He strapped sensors that measured the skin’s conductance. When we feel aroused, the sympathetic nervous system fills the sweat glands and increases the conductance.

It’s quite the basic affair, but the setup proved pretty effective at gauging what went inside the minds of these students. Pointing at the robot’s body parts didn’t seem to elicit any other than normal response, but when the 10 participants touched Nao in various locations they visibly became aroused. The more ‘off-limits’ the body part, the sweatier they became. In 90% of the participants, the strongest signal was registered when they touched Nao’s would-be genitals or buttocks.

“Social robots can elicit tactile responses in human physiology, a result that signals the power of robots, and should caution mechanical and interaction designers about positive and negative effects of human-robot interactions,” the researchers concluded.

“Our work shows that robots are a new form of media that is particularly powerful,” said Jamy Li, co-author of the study. “Social conventions regarding touching someone else’s private parts apply to a robot’s body parts as well.”

To be fair, the arousal signal doesn’t mean the students wanted to have sex with Nao. It means they became more alert, because in the back of their heads they were doing something inappropriate. In other words, the social conditioning is so strong that people can attribute human-like characteristics to something that looks and behaves like a human, although it obviously isn’t.

The implications are interesting. Home robot assistants might become very common in the coming decades. These will likely be built to look, move and sound like a human to ease awkwardness. In doing so, we might be less inclined to treat robots like a metal trash can, and more like a … friend?