James Gurney was working with some scientists studying how people's eyes move across an image naturally. here and here
Saccades occur between three and five times per second, alternating with brief periods of rest called fixations. Larger saccades for absorbing the scene, smaller ones for getting details. (which is useful for animators)
The artistic theories of composition driving the eye and of the golden mean don't appear to hold up. Dr. Edwards succinctly puts it, “abstract design gets trumped by human stories.” The job of the artist, then, in composing pictures about people is to use abstract tools to reinforce the viewer’s natural desire to seek out a face and a story. Abstract design elements do play a role in influencing where viewers look in a picture, but in pictures that include people or animals or a suggestion of a story, the human and narrative elements are what direct our exploration of a picture.
The unconscious impulses seem to include the establishment of hierarchies of interest based on normal expectations or schema of a scene. Just because an element has sharp detail or strong tonal contrasts, it doesn’t necessarily attract the eye. The dark branches behind the dinosaur’s head drew almost no attention because they fit into the natural schema of a forest scene, they didn't stand out, but the sunken log and detailed leaves did gain a lot of attention because they could house another potential threat to the characters.