1. Figural after-effects: an investigation of visual processes;Khöler;Proc. Amer. Phil. Soc.,1944
2. H. Zabrodsky, Symmetry—a review, Technical Report 90-16, CS Department, The Hebrew University of Jerusalem.
3. R.M. Boyton, C.L. Elworth, J. Onley, C.L. Klingberg, Form discrimination as predicted by overlap and area, RADC-TR-60-158, 1960.
4. Measures of symmetry;Zusne;Percept. Psychophys.,1971
5. E. Yodogawa, Symmetropy, an entropy-like measure of visual symmetry, Percept. Psychophys. 32(3).