Your jittery eyeballs enable you to notice the nasty pimples on the face of an attractive girl from a distance.

The minute, involuntary movements of our eyes enable the brain to detect the smallest details of your looks, as found by a team at Boston University led by neuroscientist Michele Rucci.

Animals with sharp tridimensional binocular vision, like humans, monkeys, felines and most birds, make continuous microscopic eye movements when they fix their gaze. This research is an important contribution to solving an enigma that has been puzzling the researchers for over 50 years.

In the '50s, rudimentary techniques involving rotating mirrors to annul the jitter for subjects focusing at an image were used.

The subjects saw a featureless gray field rather than the image, so the jittering movement was known to stop the image fading, but the precise mechanism was not known, nor other jitters' functions. The new research employed a computer to track the eye's movements. The 6 subjects were presented one of two images on a monitor: a gray background with either thick or thin central slanted lines.

In each case, the computer either kept the image still or moved it in the same rhythm with the subject's miniature jitters. The resolution was crucial: in the case of the thick lines, the volunteers could tell which way the lines slanted, no matter if the image moved or not.

This ability decreased 16% in the case of the fine-lined patterns moving at pace with the subjects' eyes.

"The result shows the eye's jitters help the brain pick out fine details, the kind involved in locating a single tree in a forest or a berry in a bush. Vision isn't like a camera, where you take a picture and the brain processes it. The actual process of looking ... affects what you see." said Rucci.

"The research makes a very compelling case for the role of eye movements in discriminating details. Vision scientists are still better at measuring and cataloging eye movements than explaining what they do so Rucci's study offers a welcome new piece to the puzzle." said neuroscientist Richard Krauzlis of the Salk Institute for Biological Studies in San Diego, California.