1 Department of Physiology and Pharmacology, Western University, London, ON, Canada; Department of Psychology, Western University, London, ON, Canada; Robarts Research Institute, London, ON, Canada.
2 Center for Vision Research, York University, Toronto, ON, Canada; Department of Physics and Astronomy, York University, Toronto, ON, Canada; Canadian Institute for Advanced Research, Toronto, ON, Canada. Electronic address: joelzy@yorku.ca.