The Uncanny Valley Phenomenon: Where Is the Categorical Boundary Between Categorization Difficulty and Categorization Failure?

The uncanny valley phenomenon has been widely discussed in relation to human-like entities, but some studies suggest it also applies to inanimate stimuli. Recently, Sasaki et al.[1] used abstract figures as stimuli and argued that categorization failure, rather than difficulty, underlies the uncanny valley phenomenon. While we appreciate their interesting proposal, we clarify that categorization difficulty and failure are not mutually exclusive accounts. We critically examine the findings of Sasaki et al.[1], questioning the lack of direct evidence for categorization failure and their reliance on non-significant results. Furthermore, we propose that the (difficulty-originated) "stranger-avoidance" hypothesis remains a viable alternative, suggesting that categorization difficulty leads to negative responses. Future research should integrate these perspectives to achieve a more comprehensive understanding. Our commentary highlights the need for collaboration and theoretical refinement in uncanny valley research.