1. Department of Psychology, University of Potsdam, P.O. Box 60 15 53, D-14415 Potsdam, Germany
2. Center for Dynamics of Complex Systems, P.O. Box 60 15 53, D-14415 Potsdam, Germany
3. Department of Physics, University of Ottawa, P.O. Box 450, Ottawa Ont., K1N 6N5, Canada