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Our Brain Sees Screen
Flickers, Even if We Don't
Excerpt By
Alison McCook, Reuters Health
NEW YORK (Reuters
Health) - Television and computer screens
update images many times a second. While we may not be conscious
of this "screen flicker," new research suggests that certain regions
of our brains register these tiny image alterations.
The fact that we see the image
as steady, and not oscillating, suggests that the brain regions
that acknowledge screen flicker do not send that information to
the rest of the brain.
"We hypothesize that the brain
operates as a kind of filter for this excess of useless visual
information," Drs. Pierre Krolak-Salmon and Marie-Anne Henaff
of the Institut National de la Sante et de la Recherche Medicale
Unite in Lyon, France, told Reuters Health in an E-mail interview.
The researchers noted that these
findings offer a reason why some people with epilepsy have seizures
while watching television or playing video games.
"For this particular population
of patients, computer screen flicker may represent a danger,"
they said. "Our findings emphasize that the brain processes this
kind of very rapid unperceived stimulus, which may represent an
overload for the nervous system."
And even people without epilepsy
may experience problems as a result of screen flicker, Krolak-Salmon
and Henaff continued.
"Computer screen flicker, when
its frequency is low, may induce headache, eyestrain and glare,"
they explained, especially in people who are prone to headaches.
Previous research has suggested
that people have less discomfort with higher frequencies--such
as 100Hz--but most televisions in France flicker at around 50Hz,
and computer screens at 60Hz to 85Hz, the authors explained.
But the authors cautioned that
people should not feel that their screens pose serious health
risks. "We do not think that people watching a computer screen
all day long have a real health risk," they said. "However, photosensitive
epileptic patients and people subject to migraines must be careful."
Experts have shown that seizures
can be triggered by lights flashing or flickering at certain frequencies,
or the geometric patterns in the video display of computer games.
This condition, known as photosensitive epilepsy, is more common
in children and adolescents and becomes less frequent with age.
The current study findings, reported
in the January issue of Annals of Neurology, are based on results
from three patients with epilepsy that did not respond to drugs
and were considering surgery to remove the portion of their brain
inducing seizures.
Before surgery, doctors implanted
electrodes in their brains to home in on the specific area originating
the seizures, and monitored the activity in these brain regions
for two weeks.
The authors found that patients
showed increased brain activity when exposed to screen flicker
in regions of the brain involved in processing visual information,
indicating that portions of their brains were "seeing" screen
flicker.
People can sidestep side effects
of screen flicker by watching plasma screens, which have no flicker,
Krolak-Salmon and Henaff said.
Krolak-Salmon also holds a position
at the Hopital Neurologique, also in Lyon.
SOURCE: Annals of Neurology 2003;53:73-80.
Reference
Source 89
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