This article argues that Ludwik Fleck’s understanding of scientific observation as a social and cultural process stemmed not only from his practical experience as a bacteriologist and serologist, but also from a confrontation with ideas developed by other Polish thinkers. It discusses ideas of three such thinkers: the ophthalmologist and philosopher of medicine Zygmunt Kramsztyk, the mathematician and painter Leon Chwistek, and the playwright, painter and photographer Stanislaw Ignacy Witkiewicz. Kramsztyk was interested in the way the observer’s preconceived idea shaped (...) observations through selection of specific visual elements and the rejection of others. Chwistek developed a theory of ‘multiple realities’ which proposed several divergent and equally valid patterns of grasping reality. In his plays, photographs, drawings and paintings Witkiewicz experimented restlessly with destabilization and transformation of the notion of a stable external reality. It links, then, debates on ‘reality’ in Poland between 1900 and 1939 to intersections of ideas derived from modern physics, psychology of perception, and avant-garde art.Keywords: Ludwik Fleck; Stanislaw Ignacy Witkiewicz ; Leon Chwistek; Poland; Perception; Avant-garde art. (shrink)