Embodied numbers: The role of vision in the development of number–space interactions

The strong association between numbers and space is found in the well-documented SNARC effect (Spatial Numerical Association of Response Codes), where responses on small/large numbers are faster in the left/right side of space, respectively. However, little is known about the developmental process through which numbers are mapped onto external physical space. Here we show that early blind individuals, but not late blind or sighted, demonstrate a reversed SNARC effect when performing a numerical comparison task with hands crossed over the body midline. Importantly, this reversed SNARC effect was not observed in any group of participants in a control parity judgment task. The present study therefore demonstrates that early visual experience drives the development of an external coordinate system for the visuo-spatial representation of numbers and further supports the idea that different types of spatial information are engaged in specific numerical tasks.