The impact of inhibition capacities and age on number–space associations.

Numerical and spatial representations are
tightly linked, i.e., when doing a binary classification
judgment on Arabic digits, participants are faster to
respond with their left/right hand to small/large numbers,
respectively (Spatial-Numerical Association of Response
Codes, SNARC effect, Dehaene et al. in J Exp Psychol Gen
122:371–396, 1993). To understand the underlying mechanisms
of the well-established SNARC effect, it seems
essential to explore the considerable inter-individual variability
characterizing it. The present study assesses the
respective roles of inhibition, age, working memory (WM)
and response speed. Whereas these non-numerical factors
have been proposed as potentially important factors to
explain individual differences in SNARC effects, none
(except response speed) has so far been explored directly.
Confirming our hypotheses, the results show that the
SNARC effect was stronger in participants that had weaker
inhibition abilities (as assessed by the Stroop task), were
relatively older and had longer response times. Interestingly,
whereas a significant part of the age influence was
mediated by cognitive inhibition, age also directly impacted
the SNARC effect. Similarly, cognitive inhibition
abilities explained inter-individual variability in number–
space associations over and above the factors age, WM
capacity and response speed. Taken together our results
provide new insights into the nature of number–space
associations by describing how these are influenced by the
non-numerical factors age and inhibition.