ABSTRACT
Intuitively, we think of number processing as an abstract and nonspatial cognitive activity. Apart from those skills necessary for mental symbol manipulation, no spatial processing seems to be involved in numerical operations. A closer inspection, however, shows that spatial and number processing are intimately connected. A link between mathematical abilities and spatial skills has been anecdotally reported in the past. Great mathematicians like Einstein explicitly emphasized the role of visuo-spatial imagery for the development of their mathematical ideas (cf. Hadamard, 1945/1996). About 15% of normal adults report visuo-spatial representations of numbers (Galton, 1880a,b; Seron et al., 1992). This suggests that the integration of number representations into visuo-spatial coordinates is not a rare phenomenon. The reported spatial layouts were predominantly oriented from left to right, were mostly automatically activated, were stable in time and had emerged in childhood.
