This article [ J. Biomed. Opt. 14, 014022 (2009) ] was originally published online on 25 February 2009. The authors wish to add an acknowledgment of a grant received.

On p. 8, the following sentence has been added to the Acknowledgments: “We also acknowledge financial support by the German Ministry for Education and Research (BMBF) via the Bernstein Center for Computational Neuroscience (BCCN) Göttingen under Grant No. 01GQ0432.”

The article was corrected online on 18 April 2011.