1. Allik, J. (1992). Psychology in Estonia. News From EFPPA, 6, 7–10.
2. Allik, J., & Konstabel, K. (2005). G. F. Parrot and the theory of unconscious inferences. Journal of the History of the Behavioral Sciences, 41, 317–330.
3. Ash, M. G. (1995). Gestalt psychology in German culture 1890–1967: Holism and the quest of objectivity. Cambridge, MA: Cambridge University Press.
4. Ball, P. (2003). Chemist Wilhelm Ostwald added colour to the art work. Nature, 425, 904.
5. Bauer, H. (1911). Die Psychologie Alhazens. Beiträge Zur Geschichte Der Philosophie Des Mittelalters, 10, 29–32.