Nerd Files

Yesterday’s offering from Delancey Place (which I just now checked), on the nature of eyes, and how they never hold still. For all the other nerds out there fascinated with ocular movement:

"As you read this, your eyes are rapidly flicking from left to right in small hops, bringing each word sequentially into focus. When you stare at a person's face, your eyes will similarly dart here and there, resting momentarily on one eye, the other eye, nose, mouth and other features. ...

"But these large voluntary eye movements, called saccades, turn out to be just a small part of the daily workout your eye muscles get. Your eyes never stop moving, even when they are apparently settled, say, on a person's nose or a sailboat bobbing on the horizon. When the eyes fixate on something, as they do for 80 percent of your waking hours, they still jump and jiggle imperceptibly in ways that turn out to be essential for seeing. If you could somehow halt these miniature motions while fixing your gaze, a static scene would simply fade from view. ...

"What is more, microsaccades may form a window into your mind. Instead of being random, these little ocular shifts may point to where your mind is secretly focusing-even if your gaze is directed elsewhere-revealing hidden thoughts and desires.

"[Researchers note] that deliberately focusing on something causes stationary images in the surrounding region to gradually fade away. This fading happens to you every day, because deliberately focusing on something can briefly slow or reduce fixational eye movements, which are also less effective outside your area of focus. Thus, even a small reduction in the rate and size of your eye movements greatly impairs your vision. You do not notice the impairment, because you are not paying attention to invisible portions of your view, focusing on what is directly in front of you instead. Totally ceasing all eye movements, however, can only be done in a laboratory. In the early 1950s some research teams achieved this stilling effect by mounting a tiny slide projector onto a contact lens and affixing the lens to a person's eye with a suction device. ... Using such a retinal stabilization technique, the image remains still with respect to the eye, causing the visual neurons to adapt and the image to fade away. ...

"In another experiment, computational neuroscientists ... found that the frequency of microsaccades also conveys the presence of something that secretly attracts a person's attention. Thus, no matter how hard you might avert your eyes from the last piece of cake on the table or the attractive male or female standing across the room, the rate and direction of your microsaccades betray your attentional spotlight. This betrayal is not a practical concern, however. In the laboratory, scientists can detect and measure these minuscule eye movements to reveal the hidden brain mechanisms of attention, but people around you cannot easily use them to read your mind--yet."

Susana Martinez-Conde and Stephen L. Macknik, "Windows on the Mind," Scientific American, August 2007, pp. 56-63.