Pre-attentive attributes such as curvature or line length tend to work because:

1. they are interpreted by the brain as a gestalt

2. When all the elements on a page share a pre-attentive attribute, this reduces cognitive load

3. they increase the cognitive load on the frontal cortex

4. the visual centre of the brain sees differences in these attributes without conscious effort

5. the eye is automatically drawn to an element that has one of these attributes