Motion along the mental number line reveals shared representations for numerosity and space

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Abstract

Perception of number and space are tightly intertwined. It has been proposed that this is due to "cortical recycling", where numerosity processing takes over circuits originally processing space. Do such "recycled" circuits retain their original functionality? Here, we investigate interactions between numerosity and motion direction, two functions that both localize to parietal cortex. We describe a new phenomenon in which visual motion direction adapts nonsymbolic numerosity perception, giving rise to a repulsive aftereffect: motion to the left adapts small numbers, leading to overestimation of numerosity, while motion to the right adapts large numbers, resulting in underestimation. The reference frame of this effect is spatiotopic. Together with the tuning properties of the effect this suggests that motion direction-numerosity cross-adaptation may occur in a homolog of area LIP. "Cortical recycling" thus expands but does not obliterate the functions originally performed by the recycled circuit, allowing for shared computations across domains.

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Caspar M Schwiedrzik

Laboratory of Neural Systems, The Rockefeller University, New York, United States

For correspondence
cschwiedrz@rockefeller.edu

Competing interests
The authors declare that no competing interests exist.
Benjamin Bernstein

Department of Psychology, Northwestern University, Evanston, United States

Competing interests
The authors declare that no competing interests exist.
Lucia Melloni

Department of Neurophysiology, Max Planck Institute for Brain Research, Frankfurt, Germany

Competing interests
The authors declare that no competing interests exist.

Ethics

Human subjects: All subjects gave written informed consent before participation. All procedures were approved by The University Committee on Activities Involving Human Subjects at New York University.

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This article is distributed under the terms of the Creative Commons Attribution License permitting unrestricted use and redistribution provided that the original author and source are credited.