Tuesday, May 18, 2010

Brain Slow-down

I was lying down staring at the ceiling fan. The fan had a circular metal piece at the center and it had the radii with ridges.  When the fan is on, I can't see the ridges, but all of us a sudden I felt I'm able to see the ridges for a fraction of a second.  I realized I could see the ridges when I was blinking my eyes.  I wasn't sure whether the vision of ridges precedes the act of blinking or the other way around.

The theory behind the persistence of vision is still being debated or debunked.  Instead of banking on a theory, I have my own explanation.

As the fan center rotates at more than 24 cycles a second, the ridges are not visible.  We can compare this to the movie watching experience where 72 or more still images are produced per second to create an illusion of motion.  When I blink, as the last image captured by the eye is processed by the brain, it doesn't have a succeeding image to perceive a rotating circle.  So, the last image is experienced by the brain as it exists - with the ridges.  When the act of blinking ends, images of the rotating circle reach the brain continuously.  So, the static image is experienced by the brain for just a fraction of a second.

I think there is some amount of slow-down in the way my brain processes the signals.  I had more such experiences.  In one instance, I could sense the experience of sound through my left ear was delayed by a fraction a second after I experienced the sound through my right ear.

I wish I could work with a neurosurgeon to understand the signal processing of the brain with such experiences.

1 comment:

Prasun said...

A friend asked me about the same phenomenon and I was intrigued to figure it out. You will see that the phenomenon actually occurs better when you make quick eye movements (saccades) around the fan. I first thought it might relate to "saccadic suppression" where when we make quick eye movements - we "supress" the fact that the image of the world is whizzing by our retina and perceive the world as stable (not the same thing if you push your finger into the side of your eyeball and perturb it - the world will move). At first I thought I had found a paper that backed this up....
I then realized that the explanation is much simpler. This article in Nature talks about the phenomenon as it relates to train
tracks. They imply that it is not a side-effect of suppression -
but the fact that your eye is kind of moving at the same velocity as
the moving object - so it is "slowing down" (stabilizing) the retinal image. You can confirm this - which blade you see (top or bottom of your visual image) changes depending on which direction you saccade. You will always catch the blade that is moving in the same direction as your eye. So really - it is kind of an "unintentional" pursuit. I think you are experiencing a bit of this phenomenon as you blink - because your eyes are saccading slightly.
Funny - I came accross your blog while Googling vJungle as I had a very nice email exchange with the CEO in the early 2000s about technology. They were way ahead of their time.