Electrophysiological Comparison of Cumulative Area and Non-symbolic Number Judgments

Abstract

Mental estimates of non-symbolic magnitudes, or magnitude representations, are recruited during action planning, decision-making, and formal mathematics. The presence of ratio effects has been used as a behavioral and neurophysiological signature of magnitude representations whereas congruity effects have been used as evidence of representational interaction. Theories diverge regarding whether evidence of ratio and congruity effects are due to overlap in representations of different magnitudes. Early interaction views put forward that there are shared perceptual processes that form overlapping magnitude representations. In contrast, late views hold that representations remain distinct and interactions occur when preparing a motor response. Research addressing these views have focused on whether perceiving differences in cumulative area, how much space is occupied by a set of objects, recruits non-symbolic number information, a similar set-based magnitude in dot arrays. The present study investigated the temporal onset of ratio and congruity effects as participants made explicit ordinal judgments about cumulative area and numerical information. Event-related potentials (ERPs) were recorded to identify whether the onset of such effects aligned with the early versus late views. A congruity effect emerged in the P100 waveform, where initial ratio effects for cumulative area and number were detected. These results align with early interaction views of magnitude processing, suggesting shared perceptual mechanisms for cumulative area and number representations. Taken together, these findings suggest that congruity effects for cumulative area and non-symbolic number judgments are generated prior to preparing a decision-response, when magnitude representations are being formed.