FROM THE FIELD • The Uncanny Valley

A Valley in One’s Sense of Affinity The mathematical termmonotonically increasing function describes a relation in which the function y 1⁄4 f x ð Þ increases continuously with the variable x. For example, as effort x grows, income y increases, or as a car’s accelerator is pressed, the car moves faster. This kind of relation is ubiquitous and easily understood. In fact, because such monotonically increasing functions cover most phenomena of everyday life, people may fall under the illusion that they represent all relations. Also attesting to this false impression is the fact that many people struggle through life by persistently pushing without understanding the effectiveness of pulling back. That is why people usually are puzzled when faced with some phenomenon that this function cannot represent. An example of a function that does not increase continuously is climbing a mountain—the relation between the distance (x) traveled by a hiker toward the summit and the hiker’s altitude (y)—owing to the intervening hills and valleys. I have noticed that, in climbing toward the goal of making robots appear like a human, our affinity for them increases until we come to a valley (Figure 1), which I call the uncanny valley. Nowadays, industrial robots are increasingly recognized as the driving force behind reductions in factory personnel. However, as is well known, these robots just extend, contract, and rotate their arms; without faces or legs, they do not look human. Their design policy is clearly based on functionality. From this standpoint, the robots must perform functions similar to those of human factory workers, but whether they look similar does not matter. Thus, given their lack of resemblance to human beings, in general, people hardly feel any affinity for them. (Note: However, industrial robots are considerably closer in appearance to humans than general machinery, especially in their arms.) If we plot the industrial robot on a graph of affinity versus human likeness, it lies near the origin in Figure 1. In contrast, a toy robot’s designer may focus more on the robot’s appearance than its functions. Consequently, despite its being a sturdy mechanical figure, the robot will start to have a roughly human-looking external form with a face, two arms, two legs, and a torso. Children seem to feel deeply attached to these toy robots. Hence, the toy robot is shown more than halfway up the first hill in Figure 1. Since creating an artificial human is itself one of the objectives of robotics, various efforts are underway to build humanlike robots. (Note: Others believe that the true appeal of robots is their potential to exceed and augment humans.) For example, a robot’s armmay be composed of a metal cylinder with many bolts, but by covering it with skin and adding a bit of fleshy plumpness, we can achieve a more humanlike appearance. As a result, we naturally respond to it with a heightened sense of affinity. Many of our readers have experience interacting with persons with physical disabilities, and all must have felt sympathy for those missing a hand or leg and wearing a prosthetic limb. Recently, owing to great advances in fabrication technology, we cannot distinguish at a glance a prosthetic hand from a real one. Some models simulate wrinkles, veins, fingernails, and even fingerprints. Though similar to a real hand, the prosthetic hand’s color is Digital Object Identifier 10.1109/MRA.2012.2192811