Further evidence that the SNARC effect is processed along a dual-route architecture: Evidence from the lateralized readiness potential

In a binary response setting, it has been frequently observed that small numbers are reacted to faster with the left hand and large numbers with the right hand (i. e., the SNARC-effect) which reflects the spatial left-right orientation of the mental number line (Dehaene, Bossini, & Giraux, 1993). In line with the work of Keus and Schwarz (in press), we investigated the locus of the conflict in the SNARC effect in a parity judgment task with the Arabic numerals 1, 2, 8, or 9. Differences between compatible (left-hand response to 1 or 2 and right-hand response to 8 and 9) and incompatible SNARC conditions (left-hand response to 8 or 9 and right-hand response to 1 or 2) were observed in the lateralized readiness potential (LRP) but not in the peak latency of the P300. In accordance with Keus and colleagues (Keus, Jenks, & Schwarz, 2005), we argue that the locus of the conflict is situated at intermediate response-related stages. However, instead of adopting a single-route processing architecture, a dual route account is proposed as the underlying processing architecture explaining the SNARC effect.