Proceedings of the Annual Meeting of the Cognitive Science Society

A large body of research has investigated humans' representation of quantity through the Approximate Number System (ANS). In contrast, it is less clear how proportions are represented, and whether proportion processing is fully analogous to numerosity processing. In the current study, we compared numerosity and proportion discrimination within the same participants, while measuring cerebral hemodynamic responses using functional near-infrared spectroscopy (fNIRS). Behavioral results showed substantial commonalities between the two tasks, including highly comparable response accuracy, and shared ratio-dependent psychophysics. At the same time, proportion judgments were slower than numerosity judgments, suggesting additional processing demands beyond shared magnitude sensitivity. Neural evidence was less diagnostic, perhaps due to insufficient power, although a group-level conjunction analysis revealed overlapping parietal activation centered on the intraparietal sulcus for a general task contrast. Together, these findings speak to the possibility of shared magnitude processing substrate spanning number and proportion, while also cautioning the equivalence of the two forms of quantitative processing.