One form of visual attention is eye movement (often assisted by head movement). Because we see more clearly close to the center of our gaze, we get more information about an object if we direct our eyes in that direction. We get coarser information (at least about shape) from objects we are not looking at directly.
Eye movements are either conjunctive or disjunctive . Conjunctive movements are eye movements that change the average direction of gaze of both eyes. Conjunctive movements can either be smooth or occur in a large, preprogrammed ballistic jump, called a saccade, which takes about 160 ms to program internally. (Marr) Saccades are rapid, but they cannot be made more often than about 5 times per second. Most people move their eyes more frequently than they realize, usually three or four times per second.
In disjunctive movements, the relative directions change, making them more convergent or more divergent, while leaving the direction of gaze unchanged. Disjunctive movements are always smooth and are under continuous control based on feedback about the disparity between the current vergence angle and the desired one.
In REM (rapid eye movement) sleep, the brain waves are very similar to those in an awake brain, hence its other name, paradoxical sleep, since the person is asleep, but his brain appears to be awake. It is in this phase of sleep that most of our hallucinoid dreams occur.