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Daniel Hyde, Elizabeth Spelke, Yaoda Xu; Parietal representation of small and large number. Journal of Vision 2011;11(11):1291. doi: 10.1167/11.11.1291.
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Behavioral and brain evidence suggests our numerical abilities are routed in two primitive cognitive systems: a parallel individuation system for representing distinct individuals simultaneously and a numerical magnitude system for representing the approximate numerical magnitude of a group of objects. In the current study, we investigated the neural mechanisms of these systems by directly contrasting processing of small (1–3 objects) and large numbers (8–24 objects), as these numerical ranges typically engage the two systems differentially. Over short blocks, observers watched a continual stream of novel images containing different numbers of objects. On half the blocks observers were instructed to press a button when the number of objects in successive images repeated (number 1-back) and on the other half of the blocks they did so for the repetition of object shapes (shape 1-back). Crucially, half the blocks were small number blocks and the other half were large number blocks. On the shape 1-back task, where task difficulty was similar for small and large numbers, distinct parietal brain responses were observed to small and large numbers. Specifically, regions of right intraparietal sulcus (IPS) responded more to large numbers whereas medial precuneus and, in some subjects, regions of the left inferior IPS responded more to small numbers. On the number 1-back task, behavioral performance was lower for large than for small numbers. Correspondingly, additional IPS activation was observed for large numbers in the number 1-back task, suggesting that some of the activity in these regions in the number task is modulated by non-numerical factors such as task difficulty. These results add to recent findings of distinct behavioral and neural signatures for small and large numbers and suggest distinct parietal brain mechanisms underlie the parallel individuation and approximate number systems.
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