I have noticed a peculiar visual effect which seems to be caused by looking at closely spaced patterns of lines under certain lighting conditions.
For example, if I’m on an escalator, the steps of which have a tightly spaced tread pattern of metal ridges, under fluorescent lighting (e.g. almost any escalator on the London Underground, or a metal travelator in an airport), then if I stare at the metal tread pattern for a few seconds, then look up, my vision is blurred for a few seconds before it rights itself.
My eyesight is normal and I have no problems focussing generally. The effect is slightly perturbing, as it feels not so much like my eyes are not focussing correctly, but more like the visual cortex of my brain has been messed around, and needs a few seconds to restore normality.
Over to the SDMB- is this normal? Do you experience this effect? What is the cause?
I get his a lot, can even force it, if I look closely at regular patterns - such as repeated patterns on wallpaper or those lines on an escalator.
I think my eyes are crossing to focus on the item, but because of the regularity of the pattern you can “over cross” but still keep the image clear.
(Crossing one’s eyes often blurs the image, but it’s easy to keep things in focus with patterns.)
Then, you look up but your eyes are still crossed a bit in such a way that everything is still clear but you have got two images, left and right that your brain cannot overlap properly to give you a true 3d image.
result: 5 seconds of spaced out weirdness.
It’s the same sort of effect that makes the eyes-crossed (rather than eyes-parallel) 3d magic eye pictures work.
Milk Milk Lemonade, that’s not it. I know what you mean- you can over- or under-cross your eyes when looking at a repeating pattern to get the ‘magic eye’ (stereogram) effect, but that’s not what I’m talking about.
Just by looking at the escalator step at my feet for a few seconds (not over- or under-crossing my eyes- looking normally), then looking up, produces the effect.
I think it’s a common effect- friends have noticed the same thing. It always seems to be under artificial light, and probably fluorescent strip lighting, that the effect is noticeable. Possibly something to do with the frequency of flicker that these lights produce.
It’s an effect similar to “strobing”, but I’m not sure this is the correct term for the effect. This effect can be seen if a TV announcer wears a striped shirt or closely striped tie. There’s likely nothing wrong with your eyes; this happens to everyone. Has to do with lighting, etc., but I can’t find a decent cite for it.