visualization

Cuoco, A. A. & Curcio, F. R. (2001). The roles of representation in school mathematics (2001 Yearbook). Reston,VA: National Council of Teachers of Mathematics.
Sutherland, R. & Mason, J. (Eds.). (1995). Exploiting mental imagery with computers in mathematics education. Berlin: Sprinter-Verlag.
Zimmermann, W. & Cunningham, S. (1991). Visualization in teaching and learning mathematics. Washington, DC: Mathematical Association of America.