THE ROLE OF COLOR VARIABILITY IN NUMEROSITY PERCEPTION: BEHAVIORAL AND NEURAL INSIGHTS

How numerosity perception is affected by visual features has been widely studied. However, little is known about the specific role of color variability as a key non-numerical visual feature in the numerosity perception at both behavioral and neural levels. The current study investigated how different levels of variability in color impact numerosity estimation and ensemble color mean performance and how these effects are reflected in neural activation patterns. Participants completed numerosity estimation and color mean estimation tasks with dot arrays with different levels of hue variability while their neural responses were recorded with fNIRS. Behavioral results showed that participants performed better in the numerosity estimation task compared to the color mean estimation task, with an interaction suggesting increased estimation errors under high color variability. Neural results demonstrated that numerosity perception and ensemble coding of color share overlapping neural networks across the PPC and PFC, including the right superior parietal lobule (SPL), bilateral inferior frontal gyri (IFG), right angular gyrus (ANG), and left middle frontal gyrus (MFG). Brain-behavior correlations further indicated that activation differences in the right SPL and right IFG predicted relative estimation errors under specific color variability conditions. Overall, the findings suggest that numerosity and color ensemble processing recruit shared fronto-parietal networks, with color variability dynamically influencing the attention resource allocations, executive control system, and the perception of Gestalt organization.