Abstract
The experimental psychologist Franz Hillebrand (1863-1926), who had been trained by Ewald Hering and Ernst Mach, worked in Innsbruck for three decades. His scientific research during this time focused on experimental investigations of spatial perception. His pioneering „alley experiments“ initiated the clarification of the important question of the geometrical structure of visual space. His study results suggest that visual space is inhomogeneous with respect to its geometry, which he assumes to be locally Euclidean or hyperbolic. Initiated by Hillebrand’s experiments, research received crucial and internationally visible input in a variety of fields such as spatial perception, the geometry of visual-spatial orientation, size constancy, as well as in the development of mathematical models and theories such as in the area of perception psychology. Additionally to the history and the results of the above-mentioned studies, the life and work of the pioneer of this research, Franz Hillebrand, will be introduced.