Both perceptual mechanisms (e.g., threat detection/avoidance) and social mechanisms (e.g., fears fostered via negative media) may explain the existence of the uncanny valley; however, existing literature lacks sufficient evidence to decide whether one, the other, or a combination best accounts for the valley's effects. As perceptually oriented explanations imply the valley should be evident early in development, we investigated whether it presents in the responding of children ( N=80; ages 5-10) to agents of varying human similarity. We found that, like adults, children were most averse to highly humanlike robots (relative to less humanlike robots and humans). But, unlike adults, children's aversion did not translate to avoidance. The findings thus indicate, consistent with perceptual explanations, that the valley effect manifests well before adulthood. However, further research is needed to understand the emergence of the valley's behavioral consequences.

People tend to anthropomorphize agents that look and/or act human, and further, they tend to evaluate such agents more positively. This, in turn, has motivated the development of robotic agents that are humanlike in appearance and/or behavior. Yet, some agents -- often those with highly humanlike appearances -- have been found to elicit the opposite, wherein they are evaluated more negatively than their less humanlike counterparts. These trends are captured by Masahiro Mori's uncanny valley hypothesis, which describes a (uncanny) valley in emotional responding - a switch from affinity to dislike - elicited by agents that are ``too humanlike'. However, while the valley phenomenon has been repeatedly observed via subjective measures, it remains unknown as to whether such evaluations reflect a potential impact to a person's behavior (i.e., aversion). We attempt to address this gap in the literature via a novel experimental paradigm employing both traditional subjective ratings, as well as measures of peoples' behavioral and phsyiological responding. The results show that not only do people rate highly humanlike robots as uncanny, but moreover, they exhibit greater avoidance of such encounters than encounters with less humanlike and human agents. Thus, the findings not only support Mori's hypothesis, but further, they indicate the valley should be taken as a serious consideration for peoples' interactions with humanlike agents.