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variable: $wmgmext -- WM/GM boundary surf extension
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default: orig (or white)

"NormSamp, Clust Controls" parameter.  To adjust,
access pop-up by L-click on "label:" (bold).

This variable affects the operation of both of
the following functions:

  write_label_timecourses_stats
  ("label:" line "T" and "S" buttons)

  paint_surface
  ("val3d:" line "PAINT" button)

This sets the surface to use when searching along
the surface normal (or along the vector to the
equivalent pial vertex).  Extensions like:

  orig
  white

will be expanded to:

  $SUBJECTS_DIR/$subject/surf/$hemi.orig
  $SUBJECTS_DIR/$subject/surf/$hemi.white
