The interaction between number and space processing and math achievement in adults

Behavioral studies show a relation between numbers and space (for a review see De Hevia et al., 2008). One instance of this link is the SNARC (Spatial Numerical Association of Response Codes) effect, consisting in faster reaction times responding to small/large digits with the left/right hand respectively (Dehaene et al. 1993). The SNARC effect has often been replicated, but it is also characterized by high inter-subject variability (Wood et al. 2006 a,b). Although differences in mathematical skills are an obvious candidate source for SNARC variability, this variable has not yet been explored systematically. For the present study, three groups of participants were recruited amongst University students; one group included only participants reporting specific problems related to numerical processing, and two control groups differing in the math requirements of their field of study (i.e. science students vs. literature students). Results confirmed that the three groups differed substantially in basic arithmetic scores [F(2,92)=19.97, p<0.001] as well as in the strength of their SNARC effect [F(2,92)=7.12, p=0.001]. The science group had the highest arithmetic score and the smallest SNARC effect and the problem report group had the lowest arithmetic score and the strongest SNARC effect, with the literature group lying in between. Rearranging the groups based on arithmetic performance yielded the same results. Correlation analyses confirmed this finding by revealing a strong relation between arithmetic scores and SNARC effect independently of group constitution [r=-0.28, p<0.01]. Different hypotheses in the context of the relevant literature are discussed.