The processing and representation of fractions within the brain: an fMRI investigation

Little is known about how adults process fractions and how fractions are represented in the brain. The intraparietal sulcus is assumed to host an analogue representation of number magnitude. It is unknown, however, how the magnitude of fractions is represented in the brain. Fraction magnitude might be represented by the numerical value of the fraction as a whole or might involve separate representations of the values of the fractions' denominator and numerator. The present fMRI study investigated brain areas involved in fraction comparison. As a diagnostic for fraction processing, the numerical distance effect (reaction times and error rates increase as the distance between the numbers being compared decreases) was evaluated. If fractions are represented as their numerical value, a distance effect is expected for the distance between the numerical values of the two fractions being compared. If fractions are represented in parts, however, that is, as the separate values of their denominators and numerators, a distance effect is expected for the distances between the two fractions' numerators and denominators, respectively. Although both types of distance effects were observed in the behavioral data, only the distance between the numerical values of the two fractions was observed to modulate activation within the intraparietal sulcus (IPS). This indicates that, within the IPS, a fraction might be represented by its numerical value as a whole, rather than by the numerical values of its numerator and denominator.