Abstract
While recent studies in adults have demonstrated the existence of a neural mechanism for a visual sense of number, little is known about its development and whether such a mechanism exists at young ages. In the current study, I introduce a novel steady-state visual evoked potential (SSVEP) technique to objectively quantify early visual cortical sensitivity to numerical and non-numerical magnitudes of a dot array. I then examine this neural sensitivity to numerical magnitude in children between three and ten years of age and in college students. Children overall exhibit strong SSVEP sensitivity to numerical magnitude in the right occipital sites with negligible SSVEP sensitivity to non-numerical magnitudes, the pattern similar to what is observed in adults. However, a closer examination of age differences reveals that this selective neural sensitivity to numerical magnitude, which is close to absent in three-year-olds, increases steadily as a function of age, while there is virtually no neural sensitivity to other non-numerical magnitudes across these ages. These results demonstrate the emergence of a neural mechanism underlying direct perception of numerosity across early and middle childhood and provide a potential neural mechanistic explanation for the development of humans’ primitive, non-verbal ability to comprehend number.
Highlights
Recent studies in adults have demonstrated the existence of a neurocognitive mechanism for a visual sense of number (Burr and Ross, 2008; Harvey et al, 2013; Park et al, 2016)
A novel steady-state visual evoked potential (SSVEP) application was developed in order to quantify neural sensitivity to numerical and non-numerical dimensions of a dot array (Fig. 1)
In adult participants, SSVEPs in the medial and right occipital (Oz & PO8 ) sites were sensitive to variations in numerosity (Fig. 2), consistent with previous results in event-related potential (ERP) (Park et al, 2016)
Summary
Recent studies in adults have demonstrated the existence of a neurocognitive mechanism for a visual sense of number (Burr and Ross, 2008; Harvey et al, 2013; Park et al, 2016). Numerical information of a dot array is processed extremely early in the cortical visual stream prior to the processing of, if any, non-numerical cues of the array (Park et al, 2016). Such findings indicating a neural mechanism for direct perception of number are consistent with the idea that our non-verbal ability to comprehend number (based on the so-called approximate number system, ANS) is developmentally and evolutionarily primitive (Gallistel and Gelman, 1992; Dehaene, 1999; Spelke and Kinzler, 2007). Functional magnetic resonance imaging (fMRI) and electroencephalogram (EEG) studies using a passive viewing paradigm have shown that infants and children’s brain, in the posterior parietal cortex or more broadly in the dorsal stream, is sensitive to changes in numerosity of dot arrays (Cantlon et al, 2006; Izard et al, 2008; Hyde and Spelke, 2011; Libertus et al, 2011)
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