Investigating the reciprocity of associations between numerical size and space

• Applicants: Dr. Melanie Richter; Professor Dr. Peter Wühr
• Subject Area: General, Cognitive and Mathematical Psychology
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 567218034

The so-called spatial-numerical association of response codes or SNARC effect describes the observation that left responses are faster and more accurate to small(er) numbers compared to large(r) numbers, whereas right responses show the opposite pattern (Dehaene et al., 1990). The regular SNARC effect thus demonstrates that numerical magnitude can influence the selection and execution of spatial responses. However, it is unclear if spatial positions can in turn also influence the selection and execution of responses that vary in numerical magnitude. This research gap thus concerns the reciprocity of the SNARC effect, which involves whether - besides the regular SNARC effect -, conversely also a reciprocal SNARC effect occurs. In this case, the SNARC effect would be bidirectional and, depending on the effect sizes, either symmetrical or asymmetrical. Our preliminary work on the reciprocity of the SNARC effect has shown that the SNARC effect is bidirectional and symmetrical for verbal stimuli and vocal responses whereas it is strongly asymmetrical for physical stimuli and manual or vocal responses. While the regular SNARC effect occurs with all combinations of stimulus and response formats, the reciprocal SNARC effect only occurs with verbal but not with physical position stimuli and thus seems to depend on the stimulus format (Richter & Wühr, 2023a, 2024a). Our preliminary work on the reciprocity of the SNARC effect and, in particular, the discrepancies in the patterns of results between the regular and reciprocal SNARC effect, have given rise to a number of research questions this research project aims to address. First, it is still unclear which task- or person-dependent determinants contribute to the emergence of the reciprocal SNARC effect. This project thus aims to examine the influence of several potential determinants including a) stimulus features such as perceptual overlap and response modality b) task difficulty and thus the overall reaction time level, and c) interindividual differences such as speed-accuracy tradeoff. Secondly, we found that none of the prominent theoretical accounts of the SNARC effect can fully explain the present pattern of results without requiring additional assumptions. Therefore, this research project aims to test the Mental Number Line (Dehaene et al., 1993), the Working Memory account (van Dijck & Fias, 2011) and the Polarity Correspondence Principle (Proctor & Cho, 2006) in their ability to explain asymmetries between the regular and reciprocal SNARC effect. In a second step, this project extends these theoretical accounts by additional assumptions required to explain the pattern of results and, in a third step, empirically tests the predictions of the modified theoretical accounts. Apart from investigating the determinants of the reciprocal SNARC effect, this research project thus contributes to the validation and further development of the existing theoretical accounts of the SNARC effect.

• DFG Programme: Research Grants