Sex robots are becoming more sophisticated, which is posing more psychological and moral dilemmas for their owners, researchers warn.

“Some robots are programmed to protest, to create a rape scenario,” Christine Hendren of Duke University told BBC. “Some are designed to look like children. One developer of these in Japan is a self-confessed pedophile, who says that this device is a prophylactic against him ever hurting a real child.”

Hendren, an engineer, and others spoke out this week at the annual meeting of the American Association for the Advancement of Science in Seattle.

A high-quality sex robot, which can retail from $8,000 to $10,000, can remember things as well as develop and understand its owner’s likes and dislikes.

“These companies are saying, ‘you don’t have a friendship? You don’t have a life partner? Don’t worry we can create a robot girlfriend for you,” robot ethicist Kathleen Richardson, who teaches at De Montfort University in Leicester, told BBC.

“A relationship with a girlfriend is based on intimacy, attachment and reciprocity. These are things that can’t be replicated by machines.”

The subject has long been debated in science fiction and was the focus of an episode of “The Twilight Zone” called “The Lonely” in 1959.