Dissociating number line estimations from underlying numerical representations.

Estimation patterns in the number line task are usually interpreted to indicate the (logarithmic or linear) nature of the underlying mental number line. However, indicators of the to-be-achieved linear representation may also be confounded with task requirements or strategies to achieve optimal task performance. In this study, we dissociated correct task performance from indices of a linear representation. Therefore, we designed an experiment in which adults and first graders had to learn number-to-space mappings of nonlinear functions. For adults, we found better fits of the corresponding functions than a linear function after just a few minutes of training. For most first graders, estimation patterns were not fitted better by a logarithmic function when they had to learn a logarithmic layout. Thus, estimation patterns produced in the number line estimation task do not necessarily allow for valid inferences on the underlying representation of number magnitude.