“The integration between the representation of non-symbolic and symbolic numbers”

Ruizhe Liu

Educated adults are able to represent numerical information in a non-symbolic and a symbolic format and flexibly switch between the two. Yet, it is unclear how these formats are integrated in the human brain. Previous studies have shown that a positive event-related potential (ERP) component peaking around 200 ms over posterior scalp sites, also called the P2p, is sensitive to ratio differences in both numerical formats. Here, we examined adults’ neural activity measured via ERPs when they were passively viewing non-symbolic and symbolic numbers simultaneously. Each stimulus consisted of an Arabic numeral overlaid on a cloud of dots. The dot quantity either matched or mismatched with the Arabic numeral. Comparing ERPs to matched and mismatched trials yielded no differences on the P2p. However, we also asked each participant to explicitly estimate dot quantities in a separate behavioral task and observed that participants tended to significantly underestimate the actual dot quantities that were shown. After adjusting the dot quantities in the EEG experiment for this underestimation bias, participants showed greater P2p amplitudes in the adjusted match condition than in the adjusted mismatch condition. These findings support the notion that adults integrate non-symbolic and symbolic number formats, but that such integration is only visible when the perceived quantity is considered.

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