1. The electric currents of the brain;R. Caton;British Medical Journal,1975
2. Über das elektroenkephalogramm des menschen;H. Berger;Archiv für Psychiatrie und Nervenkrankheiten,1929
3. An automatic low frequency analyser;W. Walter;Electronic Engineering,1943
4. An improved low frequency analyser;W. Walter;Electronic Engineering,1943