Updated: OCTOBER 22, 2019
The uncanny valley is a term coined by a Japanese robotocist in the 1970s to refer to the strong reaction of revulsion people are believed to have to robots that look uncannily realistic, but fall just short of being convincing. However, the uncanny valley theory also suggests that if robots become human enough, people's emotional response to them will turn positive again. The term, therefore, refers to the dip in people's feelings toward robots based on how human they appear to be.
This term is used in many contexts, but is becoming increasingly common in the context of sex robots and ultra-lifelike sex dolls.
More About Uncanny Valley
As sex robots continue to be developed and become more sophisticated and life-like, some people theorize that sex with robots will overtake sex between humans. However, the uncanny valley phenomenon suggests that the vast majority of people will find robots slightly "off," and will be repulsed by them.
Some of the latest robots - and even sex robots - look very human, but they fall short of mimicking essential human behavior such as eye contact and complex movement. Researchers theorize that the more human a robot appears to be, the higher the expectations our brains put on it. This creates dissonance when the robot falls short of those expectations of human-likeness.
Although a number of studies have pointed to the existence of the uncanny valley, several others have questioned its existence and have attributed the phenomenon to poor design, and even generational differences in people's response to robots.