The post - Illusion of Perception obviously confused a lot of people since I have been getting a lot of requests to explain it again.
Let me try it again with another animation.
The illusion of falling droplets is created by a pump which is pushing out the water droplets at a fixed rate. ( call it X ) - Does NOT change.
Changing the frequency of the strobe light ( call it Y ) is the integral part of the illusion.
The flow is similar to that of your shower head. The water droplets are continuously falling down. With the strobe light, we are just illuminating the droplets at different instances of time.
When X = Y —> The droplets appear stationary.
Imagine yourself to be sitting on top of the hose and watching every
drop fall through. Whenever the droplet of water is about to leave the
hose, the light flashes. This renders the droplet as stationary.
Let us call the distance between the droplets as L.
When Y > X — > The droplets appear to move up.
Now, the strobe light flashes a little too quickly than the rate of the
drop falling. This gives us the illusion of droplets moving up since you
are flashing the light before the droplet has traversed the distance L.
When Y < X — > The droplets appear to move down.
Now, the strobe light flashes a little slower than the rate of the
drop falling. This gives us the illusion of droplets moving down since you
are flashing the light after the droplet has traversed the distance L.
Thank you so much for expressing your concerns and I apologize if it had confused you. I hope this post made it up
Have a good day :)
EDIT - Here is the actual gif from the illusion of perception post.