For our project we chose a site that had an interesting roots structure. We played with eh idea of building up sections of yarn while leaving others bare. The end result was a push and pull of attention around the area. The eye was more attracted to the built up areas and more disturbed by the plainer areas.
This is a good example of one of the built up areas surrounded by the barer areas. see how the eye darts for one busy section to the next.
And here how the eye is not attracted to the plainness of the single strands.