[zeroca]

Until considering visual cortical zones and perceptive cortical visual functions, I’d like to mention, that in my opinion, any image, fallen on and then perceived by visual system (from retina up to occipital cortical stages) is result of influence of discrete light (eliminated or reflected from outer object), i.e. light influences on visual system in discrete form. Let’s analyze following observation:
After switching the light in the dark room all objects appear immediately, but they disappear at once with switching off the light, i.e. if permanent influence of light on visual system is stopped, then perception by vision also is stopped, i.e. for permanent visual perception of outer world every-instant influence of light on the retina is needed, but to the question: influence – discreet or indiscreet? I’d definitely answer, that discreet.
(Even I believe that any kind of motion in the universe and even whole motion of universe is consecutive succession of all “stopped”, instantaneous phases, but this is another theme).
But because of speed of light eye can’t perceive this discrete influence of light on the retina, i.e. the influence of each phase separately, so it perceives a permanent unmoved image of outer object. To say otherwise, if any animation, film, or motion is succession, consecutive amount of different phases, then stopped image is consecution of the same amount of phases – but of phases of the same picture. So when watching unmoved scenario, one should bear in mind that this perceived unmoved image is every-instant influence of the same image on the visual system.
Image of unmoved background is perceived as indiscreet picture by cortex, but any kind of change in this picture (i.e. motion, which is perceived in indiscreet, “smooth” form) presents quick consecutive amount of phases, and visual system isn’t able to perceive all phases!
Considered by us the example above, when lagging L1 equaled to L (post # 14 of this thread) is obvious proof of that. Eye can’t perceive motion (despite its actual taking place) until one sector of the wheel isn’t colored differently.

As I mentioned above, each point of outward object makes separate feeling (i.e. separate irritation) within elements of retina, and impulse of irritation, sent from this element of retina to occipital visual cortical center, reaches separate element of cortex as if the contours of whole outer object were copied to the occipital cortex, and as we said, each consecutive phase is overlapping on previous one at some intervals of time, and this fragmentation isn’t perceived by eye, if the speed of consecution is high!
As a conclusion I’d like to say that until existing on somatic occipital cortex image doesn’t change its place, i.e. until other parts of occipital cortex aren’t irritated, the perception of motion doesn’t take place.
Let’s recall a little about films with moving trains, the wheels of which are visible within pictures (from the remnants of these films the animations of wheels above were constructed) Why eye perceives spinning of wheel of train in two different directions? One can’t observe this event in real life.
When camera is fixed on a wheel, i.e. wheel is fixed within the frame of film picture (i.e. wheel is spinning, but not moving on the screen, i.e. it remains in the same place of screen), and perceived by eye motion of train is based on moving to opposite direction background (look at animation below), then eye will perceive it as considered above (post # 13 – spinning wheels with fixed centers).

But if in the same occasion the camera is fixed on a background (which is unmoved within film picture), but train is moving within picture, then turning of wheels will be perceived as in reality (look at animation below). The centers of wheels are not fixed, but are moving along with simultaneous turning. We can’t watch mentioned above phenomenon of oppositely moving spokes.

Anyway, the main question: why brain perceives flashing light reversal the way it does remains unanswered yet.