The effects of auditory numerosity and magnitude on visual numerosity representation: An ERP study

Abstract

Numerical representation is not restricted to sensory modalities. It remains unclear how numerosity processing in different modalities interacts within the brain. Moreover, the effect of continuous magnitudes presented in one modality on the representation of numerosity in another modality has not been well studied. By using event-related potential (ERP) and source localization analyses, the present study examined whether there was an interaction between auditory numerosity and continuous magnitude on visual numerosity representation. A visual dot array (visual standard stimulus) was preceded by sound in which numerosity (Multiple-tone vs. One-tone conditions) and magnitude (Loud-tone vs. Soft-tone conditions) information were manipulated. Then, another visual dot array (visual comparison stimulus) was presented, and participants were required to compare the numerosities of the visual dots. Behavioural results revealed that participants showed smaller just-noticeable differences (JNDs) when visual stimuli were preceded by multiple tones than those when visual stimuli were preceded by one tone. The subsequent ERP analysis of visual standard stimuli revealed that the peak amplitude of N1 was more negative under the Loud-tone condition than that under the Soft-tone condition, which could be related to better preparatory attention. Moreover, a significant interaction between auditory numerosity and magnitude was found within the P2p time window for the standard stimuli. Further source localization analysis identified the effect of N1 and P2p to be in the right middle frontal gyrus (MFG) and left inferior parietal lobule (IPL). The present study suggests that numerosity information presented in one sensory modality could spontaneously affect the numerical representation in another modality.