Perner, Josef MPI for Psychological Research (Munich, -2003), The Prior Institutes, Max Planck Institute for Human Cognitive and Brain Sciences, Max Planck Society;
Perner, J., Kohlmann, R., & Wimmer, H. (1984). Young Childrens Recognition and Use of the Vertical and Horizontal in Drawings. Child Development, 55(4), 1637-1645.