Numerosity Estimation


 A large amount of research demonstrated that adults are able to process numbers in the symbolic as well as in the non-symbolic code. According to Verguts and Fias (2004), there are qualitative differences in the coding of quantity as conveyed by symbolic and non-symbolic formats: symbolic numbers are processed with a place-coded representation whereas non-symbolic numerosities are processed with a summation-coded representation (see also Roggeman, Verguts & Fias, 2006). Moreover, besides their differential coding, symbolic and non-symbolic representations also present differential scaling; the symbolic representation being linearly scaled (Verguts, Fias & Stevens, 2005) and the non-symbolic representation being logarithmically compressed (Dehaene, 1992; Verguts & Fias, 2004). 

     The aim of our work is to examine how these different features influence numerosity estimation performances.

     Schematic representation of (A) the place-coded and linear symbolic representation and (B) the summation-coded and logarithmic non-symbolic representation. The red segment corresponds to the portion of the representation which is activated when the magnitude 40 is processed.


Study of the under- and over-estimation process


     For example, in this study, adult participants were submitted to three types of numerical estimation task: 1) a perception task, in which participants had to estimate the numerosity of a non-symbolic collection; 2) a production task, in which participants had to approximately produce the numerosity of a symbolic numerical input; 3) a reproduction task, in which participants had to reproduce the numerosity of a non-symbolic numerical input. Results showed that different patterns of performance were found according to the task used: 1) under-estimation in the perception task; 2) over-estimation in the production task; 3) accurate estimation in the reproduction task. We discussed these data by showing how they can be accounted by the direction of the mapping process that takes place between the logarithmic mental number line and the linear symbolic representation.    


- Crollen, V., Castronovo, J., & Seron, X. (in press). Under- and over-estimation: A bi-directional mapping process between symbolic and non-symbolic representations of number? Experimental Psychology.