Tuesday, April 09, 2013

visual cortex is weird

Migraine weirdness:
1. The weekend after the AF, neck was constantly sore in a weird way. No sign of headache. Soreness disappeared yesterday (Monday).
2. Monday saw waves of photophobia, but it never lasted more than twenty minutes or so, or it was low-level enough that I could adapt to it, and wouldn't notice until the ambient light changed.
3. Today, a bit of photophobia and a faint headache, slightly nauseated. Am I just hyper-sensitive? Also, this morning when I awoke, saw the m-scaled lattice that I've mentioned before; it flashes on for just a few hundred milliseconds, and fades as the morning-light bedroom scene comes into view. I would say it looks most like Form Constant III as described by Bressloff et al (no I am not on any drugs, though Bressloff prefers to refer to drug-induced hallucinations):

(This image is from Bressloff et al's 2002 Neural Computation paper. Note the coincidental opposite symmetry between this kind of m-scaled 'spiral' pattern and the ancestor map in the previous post, which can be seen as another kind of spiral lattice - something like what you'd get if you plotted a flat lattice in the visual field and looked it it in cortical space.)

Also, to reiterate an observation I made in the AF post, in light of reading all this stuff about integrated information and consciousness over the past few days: migraine scotoma are invisible, unlike the disturbingly visible grayness I saw when my left retina stopped working. The normal explanation for the invisibility of cortical scotoma is that it is "filled in", which I've always felt was fishy.. I know it's well-studied, and now I'll have to read about it.

My feeling is that there is no filling in, at least not in the way it's usually talked about, but rather that the scotoma is a scotoma in visual space period - if you don't see the space, you don't see any blankness, and you see the scene continue directly from one side to the other, not knowing any better. Maybe it's hard to justify this intuition, but I think it's similar to noting (as hemianopia patients do) that beyond the edges of the visual field, there's not an expanse of nothingness, but rather no expanse at all. If there is no expanse, there is no edge, so you get the strange condition of not being able to see the boundaries of your own visual field, because the boundary would have to be defined as between two expanses. With a proper mapping between visual direction and field location, you can be properly aware of the geometry of the visible field, without any need for it to be bounded. (Put another way, topologically, the space behind my head is equivalent to a hole in the visual field - if I can't perceive that space as being bounded by the same boundary as the visible field, why should I be able to see the boundaries, and the invisible expanse, of a cortical scotoma?)

No comments:

Post a Comment