Writing the digit 4: a key for understanding mirror reversal in children?

The first quarter of the twenty-first century has seen considerable progress in explaining the mirror writing of typically developing children. Many articles in journals and websites now explain that, as a result of the neurological phenomenon of mirror generalisation, 5-year-olds often do not know how to turn (to the left or to the right) the characters (letters and digits) and simply turn them in the direction of writing. As a result, children in left-to-right script cultures mostly reverse characters visually oriented to the left (e.g. J, Z, 1, 2, 3, 7, 9). This consequence is problematic, however, for the digit 4, which visually points towards the left and is hardly ever reversed by children. The present article, based on extensive empirical work – more than 3000 writings of the digit 4 by over a thousand French kindergarten children examined in detail – offers a statistically well-supported solution to this problem. This solution, based on a distinction of different categories of writing the digit 4, is in line with the search for correspondence between the internal direction of a character and the direction of writing in the culture. It is also in line with the historical evolution of capital letters writing.