Two uncanny valleys: Re-evaluating the uncanny valley across the full spectrum of real-world human-like robots

The uncanny valley hypothesis describes how increased human-likeness of artificial entities, ironically, could elicit a surge of negative reactions from people. Much research has studied the uncanny valley hypothesis, but little research has sought to examine people's reactions to a broad range of human-likeness manifested in real-world robots. We focused on examining people's emotional responses to real-world, as opposed to hypothetical, robots because these robots impact real-life human–robot interactions. We measured both positive and negative emotional responses to a large collection of full-body images of robots (N = 251) with various human-like features. We found evidence for the existence of not one, but two uncanny valleys. Mori's uncanny valley emerged for high human-like robots and a second uncanny valley emerged for moderately low human-like robots. We attributed these valleys to unique combinations of perceptual mismatches between human-like features, specified by a match between surface and facial feature dimensions accompanied by a mismatch with the body-manipulator dimension. We also found that patterns of the uncanny valleys differed between positive (shinwakan) and negative (bukimi) emotional responses. Lastly, the word uncanny appeared to be an unreliable measure of the uncanny valley. Implications for robot design and the uncanny valley research are discussed.