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Elliot Collins, Joonkoo Park, Marlene Behrmann; Number in the human subcortex. Journal of Vision 2017;17(10):480. doi: https://doi.org/10.1167/17.10.480.
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© ARVO (1962-2015); The Authors (2016-present)
Certain numerical abilities appear to be relatively ubiquitous in the animal kingdom, including the ability to recognize and differentiate relative quantities. This skill is present in human adults and children, as well as in non-human primates. Perhaps surprisingly, numerosity abilities are also demonstrated by lower species such as mosquito fish and spiders, despite the absence of cortical computation available to primates. This ubiquity of numerical competence suggests that representations that connect to numerical tasks are likely subserved by evolutionarily conserved regions of the nervous system. Here, we test the hypothesis that the visual evaluation of relative numerical quantities is subserved by lower-order brain structures in humans. We use a paradigm (Wheatstone stereoscope) that permits presentation of a stimulus to a single eye and compare discrimination performance when targets are shown monocularly versus dichoptically. Across multiple experiments, we show that the discrimination of displays, consisting of both large (5-80) and small (1-4) numbers of dots, is facilitated in the monocular, subcortical portions of the visual system. This is only the case, however, when observers evaluate larger ratios of 3:1 or 4:1, but not smaller ratios, closer to 1:1. Additional analyses evaluating which of 9 continuous stimulus parameters (such as size, spacing, coverage, etc.) explained participants' performance revealed that number best accounted for behavior and did so with an effect size an order of magnitude larger than any other parameter. This profile of competence matches closely the skill with which newborn infants and other species can discriminate numerical quantity. These findings suggest conservation of ontogenetically and phylogenetically lower-order systems in adults' numerical abilities. The involvement of subcortical structures in representing numerical quantities provokes a reconsideration of current theories of the neural basis of numerical cognition, in as much as it bolsters the cross-species continuity of the biological system for numerical abilities.
Meeting abstract presented at VSS 2017
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