Normal human vision is an unbelievably complex and sophisticated thing. Here is a special issue of Vision Research on one tiny component of vision - fixational eye movements and perception:
During viewing of a stationary scene, rapid gaze shifts, known as
saccades, occur every few hundreds of milliseconds. Saccades separate
fixations, the periods of apparent eye immobility in which visual
information is acquired and processed. Close inspection of oculomotor
activity in these periods reveals, however, that the very world
“fixation” is misleading: small eye movements incessantly occur in the
inter-saccadic intervals, suggesting an even deeper coupling between
visual functions and oculomotor activity. These gaze shifts come in
different varieties and are collectively known as fixational eye
movements. Although humans are normally not aware of making them, they
displace the retinal image at speeds that would be clearly visible had
the motion originated from the visual scene rather than the observer.
