1. Cybernetic Vision Research Group, Instituto de Física de São Carlos, University of São Paulo, Caixa Postal 369, São Carlos, SP, 13560-970, Brazil
2. INSERM Unite 129—ICGM, CHU Cochin, Paris, France
3. Neurons and Networks, Netherlands Institute of Brain Research, Meibergdreef 33, 1105 AZ, Amsterdam, The Netherlands