Topographic representations of object size and relationships with numerosity reveal generalized quantity processing in human parietal cortex.
Humans and many animals analyze sensory information to estimate quantities that guide behavior and decisions. These quantities include numerosity (object number) and object size. Having recently demonstrated topographic maps of numerosity, we ask whether the brain also contains maps of object size. Using ultra-high-field (7T) functional MRI and population receptive field modeling, we describe tuned responses to visual object size in bilateral human posterior parietal cortex. Tuning follows linear Gaussian functions and shows surround suppression, and tuning width narrows with increasing preferred object size. Object size-tuned responses are organized in bilateral topographic maps, with similar cortical extents responding to large and small objects. These properties of object size tuning and map organization all differ from the numerosity representation, suggesting that object size and numerosity tuning result from distinct mechanisms. However, their maps largely overlap and object size preferences correlate with numerosity preferences, suggesting associated representations of these two quantities. Object size preferences here show no discernable relation to visual position preferences found in visuospatial receptive fields. As such, object size maps (much like numerosity maps) do not reflect sensory organ structure but instead emerge within the brain. We speculate that, as in sensory processing, optimization of cognitive processing using topographic maps may be a common organizing principle in association cortex. Interactions between object size and numerosity maps may associate cognitive representations of these related features, potentially allowing consideration of both quantities together when making decisions.
Experimental Psychology, Helmholtz Institute, Utrecht University, Utrecht 3584 CS, The Netherlands; Faculty of Psychology and Education Sciences, University of Coimbra, 3001-802 Coimbra, Portugal; b.m.harvey@uu.nl.
Ben M
http://orcid.org/0000-0003-2694-618X
BM
Harvey
Experimental Psychology, Helmholtz Institute, Utrecht University, Utrecht 3584 CS, The Netherlands; Radiology, Center for Image Sciences, University Medical Center Utrecht, Utrecht 3584 CX, The Netherlands.
Alessio
A
Fracasso
Radiology, Center for Image Sciences, University Medical Center Utrecht, Utrecht 3584 CX, The Netherlands.
Natalia
N
Petridou
Experimental Psychology, Helmholtz Institute, Utrecht University, Utrecht 3584 CS, The Netherlands;
Serge O
SO
Dumoulin
D000328:Adult; D001931:Brain Mapping; D003198:Computer Simulation; D005556:Form Perception / Q000502:physiology*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008962:Models, Theoretical; D010296:Parietal Lobe / Q000033:anatomy & histology / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods; D011897:Random Allocation; D012858:Size Perception / Q000502:physiology*
high-field 7T fMRI; numerosity; object size; topographic maps