Different number-processing tasks entail qualitatively different SNARC effects

Evidence for number-space associations comes from the spatial-numerical association of response-codes (SNARC) effect, consisting in faster reaction times to small/large digits with the left/right hand respectively. Although the SNARC effect has been extensively replicated, it is characterized by high inter-individual variability (e.g. Hoffmann et al., 2014). Moreover, even though number-space associations have been observed when numerical magnitude is both relevant (e.g. magnitude comparison) and irrelevant (e.g. parity and color judgment) for successful task completion, their strengths and underlying cognitive processes seem to vary depending on whether explicit reference to numerical magnitude is drawn or not (Fias et al., 2001; Mitchell et al., 2012). To further evaluate this hypothesis, we examined whether the SNARC effects observed in a single individual during distinct number-processing tasks were systematically linked. We computed correlations between the SNARC effects measured during a parity, magnitude and color judgment task in a population of 85 healthy university students (39 females, mean age=23.44 years). Interestingly, no relation could be observed between the color (slope=-6.79) and magnitude SNARC effects (slope=-6.98; r=0.18, p=0.11), indicating that number-space associations potentially underlie different cognitive operations in tasks with and without explicit numerical magnitude processing. Conversely, the parity SNARC effect (slope=-11.58) correlated with both the color (r=0.36, p=0.001) and magnitude SNARC effects (r=0.36, p=0.001). This suggests that although no explicit numerical magnitude treatment is required in the parity task – explaining its relationship with the color task – the involvement of number semantics is sufficient to position it in line with the magnitude judgment task.