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Light afterimages called 'palinopsia'

By torachi, Jan 16, 2011 | | |
  1. torachi
    14940.jpg Q: Why do I see a streak from LED tail lights when I scan the road at night? Is this dangerous?

    A: You are seeing positive afterimages, says James Ver Hoeve, a vision scientist at UW-Madison. "If you stare at a bright red line on a white background and look away, you'll see a green line; that's a negative afterimage. If you wave a sparkler around, you'll see a streak of light that is the same color as the red-hot part; that's a positive afterimage."

    The high-intensity light-emitting diodes in some modern taillights flicker quickly, so when you move your eyes across them, you may see multiple positive afterimages with a stroboscopic effect.

    In some circumstances, the effect can be disturbing, Ver Hoeve continues. "When you see something in the center of your vision, your brain thinks, 'The object is located at a heading aligned with my eye position.' If your eyes move during a positive afterimage, your brain can misinterpret the eye movement as motion of the image rather than the eye. When motion appears to come from an object that should not be moving, the result can be disorienting."

    While negative afterimages are produced in the retina, positive afterimages are mostly formed in the brain. Past use of LSD, lesions in the brain and drug reactions have been associated with prolonged positive afterimages, Ver Hoeve says.

    The technical name for abnormal persistence of positive afterimages is palinopsia. "In Greek, 'Palin' means 'again' and 'opsia' means 'seeing.' Palinopsia doesn't mean seeing lots of Sarah Palins. It means seeing a trail of positive afterimages."

    Sunday, January 16, 2011 1:15 pm



  1. DmTryp
    My cat has issues with this. After extensive eye exams and CT scans to rule out a tumor or hemmorage of the brain, it was determined to be the result of a neurological processing problem caused by a combination of head trauma and medications. Annoying during the day, horrendous at night while driving.
  2. torachi
    The mugwump would agree that nighttime driving is a pretty serious issue, the only problem that he has that is associated with HPPD.
  3. DmTryp
    My cat believes it may have something to do with HPPD for her as well, but she has not touched LSD in almost fifteen years. She is curious as to whether or not it could be caused by n,n-DMT, which she used almost daily for over two years.
  4. torachi
    Certainly it could, specifically if maybe there were residual effects from LSD use, even if it was 15 years ago. DMT use could easily aggravate previous LSD-induced HPPD symptoms.

    Or it is just as possible HPPD symptoms could be caused by DMT usage alone. It seems to be LSD is most popular for causing HPPD symptoms, and there are a dozen different possibilities as to why, but its been known to be caused by other drugs, too.

    There is probably a DMT caused case or two out there somewhere.
  5. squeezix
    When the swimmer was young, some DMT went the rounds. Three of the swimmers older more experienced friends got severe HPPD from the experience and it ruined psychedelics for them forever. It was when they were driving that it got quite scary.
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