Why this visual phenomena?

[pokk]

Iwatch a very thin stream of oil falling from a pipe & into another pipe thru 1' of airspace. It looks like a stream until i abruptly twist my head horizontally [snaplike] & then i see droplets instead of a stream while my head is rotating [snaplike].

 

[Simon Bridge]

When you move your head quickly, you are momentarily shifting your gaze at the same speed as the droplets, allowing your eye to resolve them. When you stop, the drops are now moving past your eyes and they blur.

Similar - if you watch a ball-game, the ball, thrown close by, is a blur flying through the air unless you deliberately turn your head to follow it. When you do that it is clear. The ball just moves slower than the droplets.

 

[gsal]

When I was a kid, my mother thought I needed glasses because she noticed I twisted my head while watching cars go by...I was doing it because when I did that, I could clearly make out the face of the driver...needed glasses 20 years later, anyway...oh, well.

 

[johnbbahm]

Almost like an old engine timing light, you can see the same effect by blinking your eye fast.

 

[Simon Bridge]

That's the one - or with less effort by running a strobe light.

 

[pokk]

the oilstream is flowing down, my head/visual is snapping sideways

 

[Simon Bridge]

bet your eye's arn't.