# An Underestimation Bias in the Numerical Perception of Rewarding Stimuli: An ERP Study

## TL;DR

This study shows that people unconsciously underestimate rewarding stimuli and overestimate punishing ones when judging quantities, using brainwave data.

## Contribution

The study reveals an unconscious bias in numerical perception linked to reward and punishment, identified through ERP components.

## Key findings

- Rewarding stimuli were behaviorally underestimated compared to neutral and punishing stimuli.
- EEG data showed reward-related modulation in early visual processing (C1 component) and inhibitory processing during quantity perception (P2p).

## Abstract

Number sense, the ability to rapidly perceive, estimate, and understand relationships between quantities, constitutes a fundamental basis for mathematical cognition. However, the extent to which it is modulated by top-down regulatory processes remains poorly understood. Rewards inherently carry quantitative attributes of abundance and scarcity, and prospect theory further suggests that individuals tend to underestimate rewards and overestimate punishments of equal magnitude, implying that the perception of reward quantities may be systematically biased. To address this issue, the present study employed EEG to examine how reward-related properties of stimuli modulate number sense, using socially relevant reward stimuli as experimental materials. Behavioral results demonstrated that rewarding stimuli were underestimated compared to neutral and punishing stimuli, while punishing stimuli were overestimated relative to neutral stimuli. EEG analyses revealed that at number-sensitive electrodes (PO7, PO8, Oz), the C1 component was sensitive to reward properties; the N1 component at PO7 was specifically sensitive to punishment; and in the P2p time window, neutral stimuli elicited the largest amplitudes, suggesting inhibitory processing of reward-related attributes during quantity perception. Together, these findings indicate that reward-based modulation of number sense occurs unconsciously and follows a dynamic temporal profile.