[1] Centre for Visual Science,
[2] Research School of Biological Sciences,undefined
[3] Australian National University,undefined
[4] P.O. Box 475,undefined
[5] Canberra,undefined
[6] A.C.T. 2601,undefined
[7] Australia Tel.: +61-6-249-2409; Fax: +61-6-249-3808 email: M.Srinivasan@anu.edu.au,undefined
[8] Department of Neurobiology,undefined
[9] Zoological Institute,undefined
[10] University of Zürich,undefined
[11] Winterthurerstrasse 190,undefined
[12] CH-8057 Zürich,undefined
[13] Switzerland,undefined