VOLUME 278 (2003) PAGES 25234–25246
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The image shown in the lower panel on the left of Fig. 3A was not correct. The lower panel on the left (the first from the left) incorrectly duplicated the lower panel on the right (the third from the left). In addition, the panels in Fig. 3A were not oriented correctly. The revised figure includes the correct images in the proper orientation. This correction does not affect the interpretation of the results or the conclusions of this work.

