Excerpt from "Vision Is All About Change," by Susana Martinez-Conde, The New York Times: Gray Matter, May 17, 2013:
Every known visual system depends on movement: we see things either because they move or because our eyes do.
Some of the earliest clues to this came more than two centuries ago. Erasmus Darwin, a grandfather of Charles Darwin, observed in 1794 that staring at a small piece of scarlet silk on white paper for a long time — thereby minimizing (though not stopping) his eye movements — made it grow fainter in color, until it seemed to vanish...
What may be most surprising is that large eye motions and miniature eye jolts help us see the world in similar ways — largely at the same time.
Scientists had long believed that we used two types of oculomotor behavior to sample the visual world, alternating between big saccades to scan our surroundings and tiny ones to fix our gaze on a location of interest. Explore, fixate, repeat, all day, every day.
It seemed to make intuitive sense that we would have one brain system for exploring the environment and another for focusing on specific objects. But it turns out that exploration and gaze-fixation are not all that different processes in the brain.
See also: Choosing What We Perceive