Apple Logic Pro 9 - Manual (Page 405)

Loop repeats are displayed as extended segments of the original region, but are displayed
with less color. Each segment is the same length as the original region, and changes if
the length of the original region is changed.
Tip: If you want to create polyrhythmic structures, try experimenting with the length of
the original region.
To loop a region with the Loop parameter
1 Select the region in the Arrange area.
405 Chapter 13 Creating Your Arrangement