Have you ever seen “stars” after knocking
your head, or even if you stood up too quickly? Those tiny points of light or
other apparently visual sensations are known as “phosphenes”. Scientists are
seeking to understand as much as they can about them, not least because such
knowledge could help give a form of vision to blind people.
Here are a few facts about phosphenes:
·
A dictionary definition of a
phosphene is: “A sensation of seeing light caused by pressure or electrical
stimulation of the eye”.
·
The word comes from the Greek
for “light” and “to show”. It can therefore be expressed as “light that shines
forth”
·
Even people who have been blind
from birth can see them
·
Phosphenes are generated by the
visual cortex (at the rear of the brain) independently of stimulation from the
optic nerve
·
Phosphenes can be experienced
by rubbing your closed eyes, but can also be seen with the eyes open in a
darkened room
·
Other causes of phosphenes
include electrical stimulation, strobe lights, substances such as LSD, and
migraine headaches
·
Phosphenes can be generated
most readily when electrical pulses are applied at the same rate as brain waves
(between 5 and 40 cycles per second)
·
Many different shapes and
colors of phosphenes have been recorded, including impressions of spiders webs,
bolts of lightning and geometric shapes
·
Visions and hallucinations, as
recorded from earliest times, may have phosphenes as likely explanations
·
If phosphenes are regularly
seen during eye movements, this can be a symptom of a detached retina
·
Phosphenes may well have
influenced the work of artists such as Miro, Dali and Kandinsky
·
Children are able to see
phosphenes more readily than adults; this ability tends to decline after
adolescence
·
It is believed that phosphenes
are experienced by animals other than humans; experiments with primates shows
this almost certainly to be the case
·
The first detailed scientific
account of phosphenes was published in 1819 by Johannes Purkinje, a
physiologist from Bohemia
·
Research into phosphenes is
looking at the links between visual stimulation and brain waves; there is a
chance that linking a camera to the visual cortex could provide a means of
allowing blind people to see
The experience of phosphenes is widespread,
can have many causes, and can take many forms. By studying the phenomenon in
depth scientists hope to learn more about how the brain works and to apply this
knowledge to produce practical benefits.
©John Welford
No comments:
Post a Comment