Eye position reflects the spatial coding of numbers during magnitude comparison

Salvaggio, Samuel [UCL] Andres, Michael [UCL] Masson, Nicolas [UCL]

Behavioural studies have reported interactions between number processing and spatial attention, suggesting that number processing involves shifting attention along a left-to-right oriented continuum where numbers are represented in ascending order. However, most of these studies rely on indirect chronometric evidence. Moreover, they do not inform us about the time course of attention shifts during number processing. To overcome these issues, we used an eye-tracking device with a high spatio-temporal resolution to study gaze patterns in a task that combined the free exploration of visual scenes with the simultaneous comparison of auditorily presented numbers (from 21 to 69) to a fixed reference (45). Results showed that eye position deviated as a function of the relative magnitude of numbers during the first stages of the comparison process. Indeed, a significant rightward shift was observed when the number was larger than the reference compared to smaller than the reference, i.e. starting after hearing the number decade and lasting until response production. This finding demonstrates that tracking eye movements during free visual exploration provides a direct (i.e. gaze direction), ecological (i.e. unconstrained viewing conditions), and objective (i.e. free of experimental manipulation) measure of attention shifts during number processing.