Humans didn't evolve in an environment full of machines, and as a result we have a lot of instinctive reactions to robots that mirror our reactions to other humans. Studies have shown that people have a hard time being rude to a robot's face, just as we do with other people. We even use the same part of our brains to recognize robot and human faces. A research group at Stanford recently wondered if our instinctive reactions to robots would extend to the way we touch their bodies. And they did a series of tests in which subjects were asked to touch robots in "accessible" regions like the hands and then "inaccessible" ones like the buttocks and genitals.

The researchers will present the results of their work this week at the Annual Conference of the International Communication Association in Fukuoka, Japan. They wanted to focus on people's reactions to touch because there is already a large body of evidence showing that humans have complex reactions to touching each other, ranging from emotions to physiological changes we aren't always aware of. As robots take on the roles of caretakers, workplace helpers, and service workers, it's important to explore whether touch should be incorporated into how we design robot interfaces. But first, we need to understand whether humans react to robot touch the way they react to human touch.

To answer that question, the researchers used a human touching scale developed back in the 1960s by Sidney Jourard. Jourard used the term "body accessibility" to rank body parts based on how willing people were to allow others to touch them. As the researchers wrote:

The most accessible regions of the body were the hands, head, and arms while the least accessible region was the genitals. Does the concept of body accessibility extend to robots? If people perceive a robot as simply being a device that can be touched, we would expect no difference in response when touching one part of its body versus another, particularly if its body is of uniform texture and material. If people perceive a robot using a social lens, we would anticipate that touching low accessibility regions would elicit an emotional response associated with greater intimacy between the person and the robot.

The researchers brought study participants into a room with a small humanoid robot (Aldebaran Robotic’s NAO), who was sitting on a table. The robot was programmed to ask participants to touch 12 different parts of its body. Meanwhile, the participants were also wired up to a sensor that tested their skin conductivity. Copious research has already demonstrated that humans' skin becomes more conductive when we're "emotionally aroused." Keep in mind that emotional arousal isn't the same thing as sexual arousal—it simply refers to any strong emotional reaction, from anxiety to desire, that can be measured physiologically.

This robot touching test was designed to determine whether people would have emotional reactions to touching "low accessibility" regions on the robot, like buttocks and genitals.

Not only did study participants have an emotional reaction to touching the robot's inaccessible regions, but they also took fractions of a second longer to touch those parts as well. On an unconscious, instinctual level, humans were reacting to this little humanoid robot as if it were another person. The researchers explain:

These responses are not simply an act of playing along—they occur on a deeper physiological level. People are not inherently built to differentiate between technology and humans. Consequently, primitive responses in human physiology to cues like movement, language, and social intent can be elicited by robots just as they would by real people.

Though there are about a million jokes to be made about this study, the findings are actually quite important. They provide a major insight into UX design for roboticists, especially ones who want to build social robots that will interact with people. Knowing that humans will have unconscious reactions to robots similar to those they have to humans could help in a variety of situations. A gentle touch from a robot could be reassuring. Hugging a robot might trigger physiological reactions that are calming. Touching a robot could also trigger discomfort and even violence.

Jamy Li, one of the researchers who conducted the study, said in a release, "Our work shows that ... people respond to robots in a primitive, social way. Social conventions regarding touching someone else's private parts apply to a robot's body parts as well." This raises the question of what happens when a robot touches a human in an inaccessible body part. Maybe that will mean some robots get a punch in the face. Or they'll be welcomed in a way that hints at the future role of robots in the adult industry.