A reappraisal of the uncanny valley: categorical perception or frequency-based sensitization?

Abstract

The uncanny valley (UCV) hypothesis describes a non-linear relationship between perceived human-likeness and affective response. The “uncanny valley” refers to an intermediate level of human-likeness that is associated with strong negative affect. Recent studies have suggested that the uncanny valley might result from the categorical perception of human-like stimuli during identification. When presented with stimuli sharing human-like traits, participants attempt to segment the continuum in “human” and “non-human” categories. Due to the ambiguity of stimuli located at a category boundary, categorization difficulty gives rise to a strong, negative affective response. Importantly, researchers who have studied the UCV in terms of categorical perception have focused on categorization responses rather than affective ratings. In the present study, we examined whether the negative affect associated with the UCV might be explained in terms of an individual's degree of exposure to stimuli. In two experiments, we tested a frequency-based model against a categorical perception model using a category-learning paradigm. We manipulated the frequency of exemplars that were presented to participants from two categories during a training phase. We then examined categorization and affective responses functions, as well as the relationship between categorization and affective responses. Supporting previous findings, categorization responses suggested that participants acquired novel category structures that reflected a category boundary. These category structures appeared to influence affective ratings of eeriness. Crucially, participants' ratings of eeriness were additionally affected by exemplar frequency. Taken together, these findings suggest that the UCV is determined by both categorical properties as well as the frequency of individual exemplars retained in memory.

A review of empirical evidence on different uncanny valley hypotheses: support for perceptual mismatch as one road to the valley of eeriness

“…As discussed by Schoenherr and Burleigh (2015), the uncanny valley could represent an overarching “inverse mere-exposure effect” (ibid., 3), in which negative affect is caused by a lack of exposure to specific stimuli or stimulus categories (e.g., the authors cite the octopus as a species that is mundanely difficult to categorize). Burleigh and Schoenherr (2015) extend this idea by demonstrating that categorization ambiguity and the frequency of exposure to specific within-category stimuli contribute independently to the uncanny valley. For example, novel stimuli that were extrapolations of their original training stimuli were categorized easily but were nevertheless considered more eerie than stimuli within their training set.…”

Measuring the Uncanny Valley Effect

“…These negative evaluations are likely to persist at least until a new category is formed and labeled [58]. As stimuli that span the new category and its neighbors are categorized, categorical perception then develops along those continua [6,25].…”

Stimulus-category competition, inhibition, and affective devaluation: a novel account of the uncanny valley

“…These accounts generally consider affective response to be a function of stimulus distance from a category boundary (Cheetham et al, 2011, 2014; but see Burleigh and Schoenherr, 2015). A stimulus is easy to classify as ‘human’ or ‘non-human’ when it is far from the category boundary along a ‘human’/‘non-human’ continuum.…”