In the end, you literally see Nothing. It's truly bizarre[1]. It's not an experience I particularly want to repeat, but I'm kinda glad it happened just once, for the empathy value. It's not really something that can be effectively described if you haven't (not) seen it yourself; even now, I have trouble re-imagining the experience, 'cause my memory wants to fill in blackness or grayness or whatever. But at least in theory I now know exactly what the Nothing from _The Neverending Story_ (doesn't) look(s) like. :)
[1] What makes it even more bizarre is that migraine blindness is a strictly neurological effect- there's no damage to your eyes or optic nerves- which means you can get temporary blindsight. In my wife's case, this meant she managed to walk a couple blocks home from a friend's house, crossing suburban streets and so forth, totally normally, while all the while convinced that she was completely blind. Which, as far as conscious perception goes, was the truth!
This is the first time I've heard of anyone else experiencing this phenomenon besides myself. Have there ever been any long-term effects on you?
Mine is slightly different. I don't have migranes, for one. Also, in addition to experiencing exactly what you described (minus the migrane), sometimes I experience the inverse: I can no longer see whatever I look at, but I retain peripheral vision. For example, if I were to look at the "o" in the word "for," I wouldn't be able to see the entire word. I could still read, with difficulty, until the effect became so strong that reading was impossible. (I still had peripheral vision, sort of, but eventually paragraphs became unseeable rather than individual words.)
Whenever any of these things occurred, I was completely normal again within two hours. It was bizarre, and it's mystified myself and two eye doctors. It's only happened less than a dozen times, but it's been happening since I was very young, and my most recent was less than a year ago.
The "blindness" was exactly as you describe: not a blackness, but a nothingness.
Do you happen to have any more info about the condition? It's very elusive.
You might be experiencing a migraine without headache: https://en.wikipedia.org/wiki/Acephalgic_migraine
It's a grab bag of weird perceptual effects that can precede migrane attacks (and apparently epileptic seizures), and they can be very disconcerting if you don't know about them.
In my case (only had them once or twice), I experienced the same visual field disassociation as you did (in addition to the scintillating scotoma thing) - I could see individual things in my field of view just fine, but I could not properly combine the whole scene into a whole. Like looking at a cubist artwork - each part is reasonable but the whole doesn't fit together, or had parts missing (not holes, just discontinuities). Of course, very shortly after that started, the migrane headache arrived.
Might want to consider talking to a doctor about it; while AFAIK auras are harmless if a bit scary, if you don't have them associated with a known issue like migrane headaches, might be good to try to find out where they're coming from. Not that anyone really seems to understand the mechanisms involved.
The experience for me is absolutely identical to that of a blind spot optical illusion, except bigger and in a different area (just a bit off from the center). It's not generally obvious that there's an issue, the brain fills it in, but if I put text in that part of my vision I'll notice I can't actually read it.
The loss of foveal vision or random patches of the visual field (as opposed to gradual-leading-to-total elimination of the entire visual field) is something I have encountered a few times. As quantumet noted, auras are kind of a grab-bag, different people can have wildly different kinds of visual distortions, and some migraine sufferers don't have them at all. I know one who gets aural (hearing) distortions instead; meanwhile, I don't get any hearing issues, and my wife becomes hypersensitive to sound but doesn't experience distortion.
Migraines, generally, like seizures, are a result of mis-fires in your brain (super simplified explanation, of course). Essentially, something goes wrong such that your brain just decides that it is in pain for no particular reason (although there are triggers, just like there are triggers to epilepsy, that set of just the wrong cascade of neurons). Auras are just another manifestation of the same thing- if the thing that goes wrong goes wrong in or near your visual cortex, you get visual distortions in addition to the pain. Eventually, your brain resets, and then things are normal again, until your brain (metaphorically speaking) tries to read out-of-bounds memory, or goes into an infinite loop, or whatever else it is (again as quantumet noted, the exact mechanism is not really all that well understood), the next time.
Side note, on how everybody's auras are a little different- we just found out about a month ago that my most common aura is blue sparkles, while my wife's is gold sparkles. We knew that we both commonly saw sparkles, just never happened to mention the color before. Also incidentally, I do get auras much more often than I progress to a full-blown migraine headache.
Since the problem is neurological, eye doctors generally won't be able to figure it out or do anything about it. Generally, because eye problems can be migraine triggers. My wife starts getting headaches if she leaves her glasses off too long, and one of the first things to check when migraine frequency increases is whether her prescription has gone out of date. Other triggers are dehydration (for her) hunger (for both of us; this is a problem for me because I don't get hungry normally, so sometimes the first indication that I need to eat today is the onset of a headache) and sleep deprivation (for both of us).
My ophthalmologist detected it during a regular examination and sent out for MRI/CAT scan/spinal tap to rule out everything else, then put me on a regimen of -- oh, now I can't remember; the medicine used for altitude sickness (diamox?) and eventually "cured" me; I haven't had a recurrence since.
I guess my point is that the grandparent poster should consider seeing an ophthalmologist and/or a neurologist at their earliest convenience. (My doctor was pleased that he'd "caught it in time"; he spoke of another patient in which it had not been detected quickly enough and that person had gone blind.)
I was walking the hall to my first period, mainly looking at the bland floor tiles, and didn't realize anything was abnormal. When I happened to look up at the faces of fellow students, I noticed they had no faces, just skin colored smoothness. My hands, and text on the posters on the walls appeared in my peripheral vision, but as soon as I looked directly at anything, it seemed to disappear into an average of it's surrounding colors. I didn't freak out, but calmly walked to my first period, where I was scheduled to take a test. I made way to my desk, and marveled at this oddness, but didn't say anything, until the test was passed out and I could tell it was a page of text, but, of course, the words disappeared upon inspection. I was really impressed how useless my peripheral vision was in dealing with text or faces.
I had an awkward conversation with the teacher, who I feared thought I'd invented a disorder to get out of the test, before being allowed to visit the nurse.
The condition lasted maybe an hour. The ophthalmologist I saw shortly after found nothing wrong with my retinas or eye pressure, and declared it a visual migraine and let me go, with a newfound empathy for those with macular degeneration.
Obviously no black patch or anything like that; I first noticed the missing section (before I had visual field tests done to detect it properly) while driving, stopped at a light; I rubbed my other eye momentarily, and the traffic light vanished.
I'd like to add that I had a recent recurrence of an aura, after some twenty years! It did not precipitate in a headache, and it was the type with a zig-zag edge surrounding the blind spot: an edge of shimmering color. After it came and went, I prepared myself for a headache, but it never happened.
ps : Many thanks
[1] As far as I could search, it's close to sleep epilepsy.
This sounds like tunnel vision. I get that when I'm not feeling well (for example, some kind of gut disturbance).
It's probably worth clarifying what we mean by blind. The article and the parent comment are talking about having no light perception at all. However, many (I think most) people who are considered legally blind do have at least some light perception. The legal standard in the US is vision that can be corrected to at best 20/200 in the better eye.
While the eye which is closed receives – 'less attention' is the best way I can put it – I perceive blackness in that portion of my visual field.
People have always assumed that what I see out of my left eye is basically what someone would see out of a normal, healthy eye with a big black spot in the middle, but that's not it. I don't see blackness, I see nothing.
Not the same, but similar:
According to the Nobel Prize-winning research from David Hubel and Torsten Wiesel in the 1960s, the brain may only have a short window of opportunity in which to develop binocular vision, in which both eyes are used together. Their studies in cats, and many other studies since, suggest that if the developing brain isn’t exposed to overlapping images from the two eyes, it will never form the connections it needs to process a three dimensional scene
See the entire article: http://www.bbc.com/future/story/20120719-awoken-from-a-2d-wo...
["Oh, it's easy to understand the PHYSICS and BIOLOGY of color, but can the blind really comprehend the EXPERIENCE of color?", some might say. Alright, fine, shades of "What Mary Didn't Know", but I'm not keen to get into that.]
For example, attempt to describe a baseball. Descriptions invoking roundness and texture can be easily understood because the individual retains his/her sense of feel. But saying "it's white in color... white is actually the presence of all colors..." obviously doesn't work.
I'd be curious to hear an example of how you would explain color to someone who has been blind for life.
When a sound is close to you, it seems louder. When it's far away, it seems quieter. But sounds have other qualities which are perceived the same regardless of distance - pitch being the most recognizable. And a sound's pitch changes how you perceive it unconsciously - that is, there is a "qualia" to hearing a low sound vs. a high sound that cannot really be explained.
Similarly, visible objects which are close appear larger and those far away appear smaller. But visible objects have other qualities which are perceived the same regardless of distance - namely color. And an object's color also has a certain "qualia" that unconsciously affects how you feel about it.
This has the added advantage of making it easy to explain Doppler shift vs. redshift :)
But it's probably difficult or impossible to understand what the perception is like, and how rich it is, except by analogy when thinking about how they'd try to describe the senses the do have to someone that doesn't have them.
Our understanding of echolocation in bats or the magnetic field in birds is probably similar. We understand what they detect and how they detect it. But I don't think we have any understanding of what it's like to experience that perception.
Your brain is expecting certain input in given situations, and you have layers and layers of habits based on those expectations.
If you are accustomed to NOT having that input, you don't expect it. You don't fake it (imagining a black space of the size a visual field would be...), you just don't have it, and it's not a part of your interactions with the world.
If the shape of your visual field changes suddenly -- you're about to pass out and you get "tunnel vision" -- it's obvious and startling. If it changes gradually, you don't even notice; you just start hitting your head on low beams more often, or bumping into table edges as you go by, until you adjust (this is from experience...).