Monday, July 29, 2013

seeing spots

phosphenes aplenty these past few days, and a headache since saturday (mid-monday now), but no aura. i'll spend this post describing the phosphenes, which are interesting.

the phosphenes are always exactly foveal, less than a degree across. they are never noticeable for more than a few tens of seconds. the sensation is very similar to the very beginning of the typical aura. their appearance is very subtle, as though there is a smudge over the central view. it's comparable to having looked at the sun glinting off a surface and having a bright foveal afterimage. sometimes it seems that i can close my eyes and see a floating spot, like an afterimage, which easily fades from view; sometimes i can't see anything.

another sensation that the phosphene is similar to is lustre or shimmering as from interocular conflict. earlier today i found myself gazing into the distance above my desk, thinking about something, and thought i was seeing a spot; then after a few seconds i realized that my left eye was seeing a mark on the underside of a plywood shelf, where a screw pokes out, with my left eye, while the same view by the right eye was occluded by a hanging piece of paper. once i understood what i was seeing, the sensation seemed to change; it is as though i am strongly sensitized to the onset of the aura, and when i think i am seeing it, or seeing these blippy phosphenes, i feel that i know i'm seeing it, which turns back around and affects the way it feels to see it.

a third way of describing the sensation is as scotoma-like, but there is never any scotoma, or at least not any so large or stable that i can see it. it's more like what is seen is interfered with; maybe it's a scotoma in the confluence? mostly in V2/V3?

anyways, the foveal spots are always brief. in the past few days i've noticed them a dozen times. during the same period, i've repeatedly noticed the familiar difficulty with reading text, especially in the morning. i look at black text on a white background, and it's very difficult to read, as though the letters are jumbled. i think what's happening is that the afterimages aren't being properly suppressed, and that it's only noticeable with the high-contrast stimulus of black-on-white text, especially on a computer screen where the white is really bright. at other times i've noticed problems with afterimages, especially of textures, seeming to 'stick' from fixation to fixation, thinking that i see something in one location when it's actually carried over from the previous fixation. these sensations aren't afterimages in the common sense of light impressed in the retinas, which have their characteristic slow fuzzy fade; they are clearer and sharper at the same time that they are less substantial.

a headache started saturday sometime, then disappeared, then reappeared yesterday, subtle - only noticed it when changing posture - and remains today, where it was slightly excruciating earlier and mostly gone now. right trigeminal nerve, felt it above the right eye at the supraorbital nerve, and above my upper right teeth.

Tuesday, July 23, 2013

halted aura

today in the lab, around noon, started to get really light sensitive, felt very unsteady, a little nauseated. for the past couple of days kept seeing weird flashes of blue light, like lens flares in the j.j. abrams jokes. also, i've noticed the eye crank lines more than usual in recent days, of course when making extreme eye movements, but not really extreme. i feel like the visibility of those phosphenes is linked to the migraines.

as the day went on, it (the discomfort) basically got better. had a coffee around 4, after that i don't remember being bothered so much, just had half the lights off in my office.

then, about 7:15, wrapping up my files, and notice it's hard to see; then discover a fairly well-developed scotoma in the left field, less than 5 degrees out. for whatever reason i hadn't noticed it up to that point - i don't remember exactly what i'd been doing for the few minutes previous, probably reading something, which is when i usually notice.

so i got out my tracking program and had some problems - one problem was that the new target i had set up was just too phosphene-like. it was a dumb idea, flickers too much, too noisy. better to just have a slow-counter-phasing block like a perimetry target. even when i could find the aura, it was hard to set the target. which leads to the second problem: the scotoma was weak. i think that even when i did find it, the target shone through, which i've never seen before. usually the scotoma is absolute, and i did find some times/places where it seems the target (or my finger) really were invisible; but, it also seemed that i could pass the target over what felt like a scotoma region, and its contrast would seem to attenuate, but it wouldn't disappear.

i got a couple of 1-2 minute recordings, breaking in between, and then the aura evaporated. it seemed normal in its geometry, if faint, barely ever saw the fortification spectrum, but at some point - i'd say 15 minutes into its normal course, barely 10-20 degrees out, it just disappeared and didn't come back. i think i stopped the second recording around the time it disintegrated, so i have a record of where it was. it was weak and small from the start, so the CSD wave must have just disintegrated. very strange. for a while after, a few minutes, i had a clear feeling of visual disorganization in the left field, but nothing obvious, nothing i could really pin down, and certainly no scotoma.

no headache whatsoever - there was a slight headache in the afternoon, right side, normal place, but transient and weak, i gave it a 0.5.

came home and had dinner, bit of a weird feeling but nothing significant. weird.

Friday, July 19, 2013

cat vision

Sharpness is, really, an illusion. It doesn't represent anything about the world, it's just an indication that the limits of resolution of the visual system have been met. In that sense, it's relative. I've thought about sharpness a lot, starting in graduate school, when I first wondered whether, having learned the quantitative difference in visual spatial resolution between cat and human, a cat could see stars. My first thought was no - stars are so small, if blurred they can't be seen; then I recognized that human acuity is nothing special (a sort of Copernican principle for vision), and that sure, cats should be able to see stars just as humans can. But they would look different, wouldn't they? Blurrier? No. To see blur implies you have the acuity to see what is missing. So then, they would look larger? No, for the same reason - if a star appears as a disk, that implies its edges are seen separately, which implies acuity to separate them. So to a cat, whose acuity is almost an order of magnitude worse than a human, stars must also appear as points. How to make sense of this?

This gets at a more general sort of paradox about visual resolution. Lower acuity isn't the same as blur, not at all. Acuity is an ability or a capacity; blur is a state or an affordance. A certain acuity enables you to see a certain amount of blur - that is the relationship. But we easily confuse the two by trying to represent the effects of acuity as blur. This is a common demonstration: illustrate the spatial resolution of the visual field as round window with a focused center and increasing blur towards its boundaries. This kind of demonstration is useful in that it shows what is lost in peripheral vision (in terms only of 1st-order resolution) relative to central vision. But it is harmful in that it conflates blur with this relative difference in visibility. Because really, no matter what the resolution is, there is finer content that cannot be seen.  We can think of this kind of demonstration, of comparing resolution at different visual field locations in terms of blur, an 'isometric' demonstration, since space is kept constant or symmetric over the whole field, though apparent sharpness falsely appears to change. This demonstration doesn't violate our intuitions about space - space seems, and is, symmetric to translations across the visual field - though it does fool us regarding blur.

Another way of demonstrating the same variation in resolution across the visual field is to reverse this relationship; that is, with an isoambylic representation of the field. This representation would have equal sharpness everywhere, but would vary metrically across the field, giving something like a fish-eye lens view of the scene. For some reason, even though the isoambylic representation is just as 'fair' as the isometric, its distortions are more disturbing. Maybe it's because the spatial asymmetry is unfamiliar, whereas blur asymmetries are more familiar.

So now we go back to cat vision. Imagine that you and a talking, scientifically interested cat, are discussing the topic at hand, and wondering how to explain to one another the differences in your spatial acuity. I think it's time for a dialogue!

Tacitus: So, here we are.
Otho: True.
Tacitus: We're supposed to demonstrate to one another the differences in our visual fields, in terms of spatial acuity. How do you think we might do that?
Otho: Well, for starters, let's use pictures.
Tacitus: That's kind of a given.
Otho: Good. Here are two copies of a scene. The one on the left represents your acuity: you see that in the center, the image is sharper, and it gets blurrier as you go out towards the edges.
Tacitus: I do see that. Nice and sharp in the center, blurrier toward the edges.
Otho: If you stand right here, and look at the center of the picture, you shouldn't be able to tell that there's any blur, because the blur is matched to your acuity. What do you see?
Tacitus: It's just as you say. Interesting!
Otho: Good. Now, this picture, on the right, represents my acuity. It's similar in that in its center, it's sharper, getting blurrier towards the edges.
Tacitus: I see that, but...
Otho: But what?
Tacitus: But it looks just like my picture. I can't see a difference. Maybe.. it's not quite as strong a trend, from the center outward, but I can barely tell.
Otho: Well, the difference is obvious to me. It's because my acuity is so much better than yours, all around.
Tacitus: Well, then this isn't fair. Why can you see so clearly the difference between our visual fields, while I can't see it at all? I feel left out.
Otho: Hm.
Tacitus: Here, let's try this. Instead of using blur to represent acuity, let's change the size of the images. We'll transform the images so that the acuity limit, which is just a measure of distance within the visual field, will be a fixed distance.
Otho: So that means that when acuity is high, the image will be relatively magnified, since you're taking a small distance in the visual field and stretching it to, let's say, one centimeter. And when acuity is low, the image will be compressed, since you're taking a big distance in the field and squeezing it into that same centimeter.
Tacitus: Exactly!
Otho: The images will look funny, though.
Tacitus: Well, the funny-ness will be our explanatory tool. We should both be able to notice changes in size, right? I can see a spot a centimeter across from this distance, and so can you.
Otho: It does seem fair.
Tacitus: Okay, here we go.
Otho: Wow! My visual field is so big! And look at the distortion, it's like a fish-eye lens! Why is your field so small?
Tacitus: Didn't you just explain it to me?
Otho: I know, I was just surprised.
Tacitus: And mine also looks like a fish-eye lens, just a bit less extreme. Yours is interesting, I can see so many details there that I can't see in mine. I didn't realize you could see such small things!
Otho: I'm sure you did, you just haven't realized it in a visual sense.
Tacitus: Well here it is.
Otho: Can I go back to bed now? It's 3am.
Tacitus: Go ahead and try. We'll see how it goes.

Thursday, July 11, 2013

prime day

today is a prime sequence day: 7-11-13. this is the next-to-last time this will happen this century; the last one will be 11-13-17. Last Prime Day sounds ominous.

the preceding is only really true in places, i.e. the USA, where we use the month-day-year notation for dates (and if we ignore the century count). if we use the more typical ordering of day-month-year, the Last Prime Day will be this November 7th: 7-11-13, and then no more until the 1st of February, 2103. (the first American Prime Day of the next century will be January 2nd of the same year).

Thursday, July 04, 2013

titles are hard

woke up this morning, after nine, opened then closed my eyes, and saw a glittering arc in my left visual field: this is the fourth or fifth time now, at least (i could pin it to one of those if i looked back over these records) that this has happened as i awoke. the aura was typical, about 10 minutes or so in, already with the leftward midline jag, then arcing downward. like last time, when i woke in the middle of the night at a similar stage, i decided not to run and record the end of it, just laid there and observed.

i watched half of it with eyes closed, and the scintillations were a bit plainer that way, typical fortification spectrum. i noticed that even - or especially - with eyes closed, eye movements seem to briefly abolish my perception of the scintillations. with eyes open, the same seems to happen, but it's less plain. the scotoma was very thin, which i've noticed before with the early morning (and the previous, nighttime) auras.

a few minutes after i awoke the headache started, and i gave it a 3. left side aura, headache focused on right frontal nerve. might have peaked at 4 or so around or after noon, when i could feel it in my teeth, but now it's more like a 1, i have to shake my head or stand up to feel it.

july fourth! getting work done lately. checked the proofs of one paper and submitted another. need to revise a third. need to work on a fourth and a fifth, editing and improvements of unsubmitted papers. and then there's a sixth that needs to be written, outlined it in toronto. so it's been a good summer for papers, at least.

that's it for now. spending july 4 playing video games, need to get back to that before it's time to cook dinner.