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Updated: Sep 16, 2025

Investigating Object Representations in the Macaque Dorsal Visual Stream Using Single-unit Recordings
Published on: August 1, 2018
Distinct neural representational geometries of numerosity in early visual and association regions across visual
Alireza Karami1, Elisa Castaldi2, Evelyn Eger3
1Center for Mind/Brain Science, University of Trento, Rovereto, Italy. alireza.kr@gmail.com.
Abstract:
Visual numerosity, traditionally linked to the parietal cortex, is now thought to be represented across a broader cortical network, including early visual and associative areas in both streams. However, how numerosity is encoded relative to other visual features remains unclear. We conducted a whole-brain functional magnetic resonance imaging (fMRI) study with thirty-one adults performing a numerosity estimation task on visual sets varying in number, item size, total item area, field area, and density, ensuring tight stimulus control. Using model-based representational similarity analyses, we found numerosity represented independently of other visual properties in early visual areas and amplified in retinotopic and non-retinotopic associative regions across both streams. Dimensionality reduction of BOLD patterns revealed distinct geometries: a one-dimensional representation of numerical rank in early visual and ventral retinotopic areas, and a curved structure encoding rank and distance-to-endpoints in associative dorsal and ventral regions. These results demonstrate distinct neural coding schemes for numerosity across cortical regions.
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