1. Department of MathematicsUniversity of Pittsburgh 301 Thackeray Hall Pittsburgh PA 15260 USA
2. School of PhysiologyPharmacology & NeuroscienceFaculty of Life SciencesUniversity of BristolBiomedical Sciences BuildingUniversity Walk Bristol BS8 1TD UK
3. Center for the Neural Basis of CognitionUniversity of Pittsburgh 4400 Fifth Avenue Pittsburgh PA 15213 USA