On Thu, 4 Nov 1999, Faith L Florer wrote:
> Does anyone here know why it is that the numbers on a digital clock (and
> some images on a television screen) appear to jiggle when a person is
> using an electric toothbrush?
>
> I was asked this question in cognition class.
This is not a perception question! Fortunately for you, it was asked
in cognition class, so that makes it all right (just joking, of
course, at least on this list).
In a former life I took a physics course or two, which still leaves me
totally unqualified to answer this question, so naturally I will. The
electric toothbrush has an electric motor. When it operates, it
produces electromagnetic waves (electrical noise) which is picked up
by the TV set, causing interference within the TV electrical circuits.
This causes the image to become unstable. I guess the same thing can
happen with other electronic devices, even those not designed to
receive electromagnetic energy.
Your student could test this by running other devices with electric
motors and seeing if they produce a similar effect (try the vacuum
cleaner). Or he or she could give up tooth-brushing while watching TV.
At one time I did some single-unit extracellular recordings from
neurons. The electrical activity of the neurons was highly amplified,
and we continually had to struggle to eliminate sources of electrical
noise from fluorescent lights, elevators, you name it, which
overwhelmed the signal. We would put the animal within a wire-mesh
cage which, primarily in theory but not so well in practice, shielded
the animal from this electrical interference.
Now there's a suggestion. Tell your student to build a wire-mesh cage
around the TV. Then she can have clean teeth and a stable TV picture
at the same time.
-Stephen
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Stephen Black, Ph.D. tel: (819) 822-9600 ext 2470
Department of Psychology fax: (819) 822-9661
Bishop's University e-mail: [EMAIL PROTECTED]
Lennoxville, QC
J1M 1Z7
Canada Department web page at http://www.ubishops.ca/ccc/div/soc/psy
Check out TIPS listserv for teachers of psychology at:
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