MODULE: Anatomy of the eye

Step 04 of 07: The eye is not a camera

Now despite serving a similar function, the eye is not the same as a camera, which also uses a lens to focus an image onto some photoreceptive surface. The critical difference in anatomy is that our visual apparatus is flexible, the lens can expand and contract, rather than the rigid lens of the camera that is focused through movement forward or back. Beyond that our eyes favour movement and are constantly in motion, so rather than simply capturing the optic array, our eyes are trained to observe the optic flow, or changes in the capture of light from moment to moment. During saccades, movements of the eye, we can even be persuaded to perceive movement when there is none;

Professor KITAOKA's rotating snake illusion — Figure 2. Movement occurs as you glance over the illusion,
but slows when you focus at its centre. (copyright 2003 Professor KITAOKA, Ritsumeikan University, Kyoto)

Short activity

Take a look around composition. You should notice some parts seem to rotate.
Now stare directly at one of the central dots. Does the rotation slow or stop?
Now quickly jump to a neighbouring dot then stay there for 1 or 2 seconds before jumping to the next dot. If you repeat this, you should notice a start-stop reaction of perceived movement. This is also proof the image is illusory and not an animated GIF.