Effect of electric toothbrush on Visual Perception

Robert Steven steven at MSHRI.ON.CA
Sat Jun 1 11:50:12 EST 1996

>Maybe some of you neuroscience folks can answer me this one:
>As I was brushing my teeth with an electric toothbrush, I happened to
>look obliquely at my computer monitor screen and noticed that while I
>was doing this the screen seemed to flicker or vibrate.  Only the
>When I shut off the toothbrush, nothing.  When I took the toothbrush
>out of my mouth and left it on, aiming it at the monitor, nothing.
>When I created the same sound as the toothbrush made in my mouth by
>pressing it while it was turned on into my hand, nothing.
>My guess is that the sensation of the toothbrush on my teeth does
>something to my visual perception.  I realize that a computer screen,
>like a TV set is essentially a fast strobe light.   Is there a name for
>this, or am I having a seizure?
>MikeG994 at ix.netcom.com

How about this for an explanation/guess. You mention that you see the flicker
when you look at the screen obliquely. This I believe is due to the fact that
your peripheral vision is more sensitive to motion than your forward vision. The
computer screen is redrawn line by line at a certain "refresh rate". Below about
70 Hz your peripheral vision can detect the redrawing of the screen as a
flicker. Above 70 Hz even your peripheral vision can't notice the redrawing of
the screen. This is a good test when you're buying a computer monitor by the
way, if it flickers when you look at it with your peripheral vision don't buy
it - get a Macintosh.

Anyway, what I think you've got is a monitor that has a refresh rate around 70
Hz and you don't normally see any flicker when you view it with your peripheral
vision. But when you vibrate your head with the toothbrush, it somehow affects
your vision so that the flicker becomes noticable. I don't think it depends on
the frequency of the toothbrush vibration because I've noticed the same thing
when I just click my teeth together while chewing food!

steven at mshri.on.ca

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