Visual similarity modulates visual size contrast

Perception is relational: object properties are perceived in comparison with their spatiotemporal context rather than absolutely. This principle predicts well known contrast effects: For instance, the same sphere will feel smaller after feeling a larger sphere and larger after feeling a smaller sphere (the Uznadze effect). In a series of experiments, we used a visual version of the Uznadze effect to test whether constrast effects can be modulated by higher-level factors, such as the similarity between the contrasting inducer stimulus and the contrasted induced stimulus. Our results suggest that the answer is positive for some dimensions of similarity, but not all. In particular, we report that size contrast is weaker for inducer-inducing pairs having the same shape but different colors, in comparison to the same color; for pairs having the same color, but different shape in comparison to the same shape; but that size constrast is unaffected by dissimilarity in orientation of gratings embedded in similar shapes. These findings complement related work in haptics (Kappers & Tiest, 2014) in suggesting that relational determination in perception can recruit high-level factors.