Measuring the acuity of the approximate number system in young children

The approximate number system (ANS) is a hypothesized mechanism responsible for the representation and processing of numerical information in an imprecise fashion. According to the predominant theory, the ANS is essential in solving simple numerical tasks such as comparing which of two quantities is numerically larger, and some research has indicated that individual differences in its acuity influence higher-level mathematical performance. Because of this far-reaching role of the ANS, it is essential to assess its acuity with measures that are reliable, and valid. The present work reviews and synthesizes many of the methodological problems that are relevant for measuring ANS acuity in young children. We discuss issues related to task comprehension, the role of non-numerical perceptual properties of the stimuli, the role of inhibition, and the appropriateness and reliability of the ANS acuity indices. Recommendations and open questions are summarized.