AUTHOR CORRECTION
Vol. 26, no. 7, p. 2758–2771, 2006. Some figures presented composite images. These images are delineated by the insertion of white lines in the corrected versions below. These changes do not affect the conclusions of the study.
Page 2762, : Panels C and D should appear as below.
Page 2766, : Panel E should appear as below.
Page 2768, : Panel E should appear as below.