Early research on spatial hearing by Alvar Wilska (1911-1987)

This contribution introduces a surprisingly modern but nearly completely unknown binaural work from 1938 by Alvar Wilska, whose 100th anniversary was celebrated on March 14, 2011. It was performed at the Institute of Physiology of the University of Helsinki as part of his doctoral research and was published under the title: Untersuchungen über das Richtungshören (Studies on directional hearing). The original German text was rediscovered by one of us (AK) in 2006, and only after the ingenuity of this research had really been understood was an English translation produced in cooperation between Espoo and Eindhoven under the inspiring leadership of Matti Karjalainen (http://www.acoustics.hut.fi/publications/WilskaThesis/). The work in the thesis revolves around two experimental questions: 1. What is the influence of external factors, e.g., stimulus parameters, on spatial hearing? 2. How do signal parameters influence localization accuracy? Wilska performed his experiments by placing subjects in a spatial sound field, where source directions were adjusted by re-orienting the subject in three dimensions while keeping the source location fixed. Alternatively, he performed sound field analyses and listening experiments by making use of a self-built dummy head that was based on a male cadaver. It consisted of a realistic reproduction of the head, pinnae and ear canals, and contained self-constructed condenser microphones placed at the positions of the ear drums. In this way he was able to measure interaural time and level differences for all source directions. The paper presents an overview of Wilska's thesis research, with specific emphasis on his understanding of the role of onsets and envelope fluctuations in sound localization.