Our brains detect and analyze myriad features of the world, and we all know that it does much of this work automatically. One thing it can do, seemingly without effort, is detect how many things are in a set or collection. (This isn’t counting, which is different.) The ability is called “numerical competence” and is widespread in animals that include insects but apparently not the unelected trolls who are firing people at NSF and NIH. Seriously, numerical competence is important for survival and reproduction, and the feature being detected is called numerosity.
A new paper in Nature Communications looks in detail at the brain regions and systems that detect numerosity, specifically asking how our brains detect absolute numerosity and then move to detecting/computing relative numerosity. The authors show that absolute numerosity is detected in the first stages of processing in the visual system, but that even at that early step, the brain is estimating relative numerosity. As processing moves into other “later” brain regions, relative numerosity is the focus. In their Discussion, the authors summarize this finding and suggest that it might apply to other wondrous capacities of our underused brains:
By illustrating that the representation of relative numerosity emerges through this hierarchical process, our study goes beyond these previous studies and introduces an additional dimension of abstraction: the transition from absolute to relative numerical magnitude. We speculate that this abstraction process might be a fundamental principle in magnitude coding, potentially offering more efficiency and robustness, and might even be applicable across other domains.
Hierarchical representations of relative numerical magnitudes in the human frontoparietal cortex
In Nature Communications, 6 January 2025
From the labs of Yuko Yotsumoto and Masamichi J. Hayashi.
Snippet by Stephen Matheson
Image credit: Figure 3 from Kido et al. linked above (CC-BY-NC-ND)