The mental number line and the working memory line: Their relationship investigated throughout the school years.

Numerical magnitude is known to be represented in long term memory as a position on a spatially oriented mental number line, as measured by the spatial numerical association of response codes (SNARC) effect. Recently, it has been discovered that serial order in verbal working memory is also represented as positions on an oriented mental working memory (WM) line, as measured by the ordinal position (OP) effect. This led to the WM account that postulates that the SNARC effect re?flects a temporary WM representation. If this is the case, one would expect the development of both the SNARC and the OP effect to be related. An alternative proposition, the dual account, postulates that the SNARC is a long-term semantic magnitude representation, whereas the OP reflects serial order WM and that both effects are independent. In a large-scale study across primary and second?ary education, the relation between the two effects was investigated. No significant correlations be?tween the two effects were found in any of the different age groups. Additionally, bootstrapping techniques were used to evaluate the consistency of the effects within participants. These analyses showed that there was only a very small minority of the participants that showed consistency for both effects. This further demonstrates the independence of the two effects. We conclude that the mental number line and mental working memory line bear no relation with each other.