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. 2012 Apr 19;7(4):e35530. doi: 10.1371/journal.pone.0035530

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de Hevia et al.

This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited.

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(top) a positive mapping between numbers and length; (center) a positive mapping between brightness and length; (bottom) a positive mapping between numbers and brightness.