When color "counts": evidence of color-selective numerosity adaptation

Perceptual adaptation is considered a key mechanism enabling reduced computation of redundant environmental information to allow increased sensitivity to deviants. Like other primary visual properties, the perception of numerical quantities is susceptible to adaptation. Previous findings showed that numerosity adaptation is not linked to the basic, non-numerical, perceptual features of the items such as contrast, size, and orientation, suggesting that numerical-related short-term plasticity has a rather coarse environmental tuning. In the present work we investigated whether numerosity adaptation is sensitive to a highly salient visual feature such as color. Our results revealed that the magnitude of numerosity adaptation strongly depends on the perceived color similarity between the adaptor and the test stimulus. Specifically, when the two stimuli shared the same color, the perceived numerosity of the test was compressed by around 25% but remained close to veridical when the adaptor had a different color. In agreement with previous findings, our data also showed that such a selectivity did not occur when a less salient visual attribute, like orientation, was used. Taken together, our results support the idea that short-term visual plasticity associated with visual numerical cognition is selectively tuned to highly salient visual attributes like color. This selectivity may have evolved through its behavioral relevance.