At the beginning of the 20th century, artists began to seek new ways of expression. German expressionists established a particularly revolutionary approach. They rejected the ideals of the bourgeois salon painters and began instead to adhere to principles of absolute subjectivity, emotional expression and a return to techniques, forms and subjects that were considered by many to be barbaric and primitive. The artists emphasized emotion over intellect, instinct and intuition over received wisdom, and dreams over reality. All these elements were once and commonly included in the artworks of indigenous peoples, children’s paintings and the works of the mentally ill. All ultimately became fundamental sources of inspiration for modern art.
It was the collection at the hospital in Heidelberg and Prinzhorn's book Bildnerei der Geisteskranken that fundamentally influenced a great number of avant-garde artists, such as Alfred Kubin, Paul Klee, Oskar Kokoschka, Max Ernst or Pablo Picasso. They often intentionally referenced the works of the mentally ill in their own efforts. In them they saw an oasis of absolute creative freedom that could never be achieved through mere rigid education alone. Prinzhorn's book led to Jean Dubuffet becoming passionately interested in the concept of spontaneous composition. This later culminated in the artist formulating the concept of art brut.