Human quantity processing, from sensory to cognitive systems

Human perception of physical quantities like numerosity and event timing  supports many cognitive functions, from foraging to mathematical and scientific thought. Investigation of the underlying neural processes has focussed on quantity-tuned neural responses, which respond maximally to different numerosities or timings in different neural populations. Here I will describe 7T fMRI studies in which we show tuned neural populations in many areas of the human brain and for many quantities. These are spatially organised to map the quantity across the cortical surface. I will then discuss recent studies in which we reveal how these quantity-tuned responses are derived from responses in sensory systems, how they are then transformed between different brain areas, and how responses to different quantities are related. I will first show how straightforward analyses of visual images can determine their numerosity with little effect of item size or spacing, and that this analysis predicts responses to numerosity in early visual cortex and neural network models more closely than numerosity itself. Finally, I will describe a set of brain areas whose responses depend on working memory load near those showing quantity-tuned responses. I propose that this grouping allows a linking of physical quantity representations and working memory, supporting quantitative and mathematical tasks. Together, these results give an integrated overview of quantity-tuned neural response, their derivation in sensory systems, and their extension into higher-level cognitive processing.