A self-organizing learning account of number-form synaesthesia.

Some people automatically and involuntarily "see" mental images of numbers in spatial arrays when they think of numbers. This phenomenon, called number forms, shares three key characteristics with the other types of synaesthesia, within-individual consistency, between-individual variety, and mixture of regularity and randomness. A theoretical framework called SOLA (self-organizing learning account of number forms) is proposed, which explains the generation process of number forms and the origin of those three characteristics. The simulations replicated the qualitative properties of the shapes of number forms, the property that numbers are aligned in order of size, that discontinuity usually occurs at the point of carry, and that continuous lines tend to have many bends.