Tuesday, January 17, 2006
Scanning the Visual Cortex
Here's an interesting phenomenon I've observed a few times, when I am in a state between sleep and wakefulness. I was in a dim room, just dozing off, when I was just conscious enough to notice a tachistoscopic effect. It was as though I was seeing a series of visual shapes in rapid succession, but with no logical connection between them other than shape. For example, imagine a series of round shapes: an orange, a basketball, the setting sun, a wedding ring, etc. It was as in a film, when an image is retained for just a single frame, immediately replaced by another one. However, the images were more or less registered with each other (i.e., about the same size and position). The first time this happened, I woke up as soon as I concentrated on it, but remembered the sensation. The second time it happened, weeks later, I tried to observe it longer without waking up, sort of like lucid dreaming. That worked for a while, but then I woke up again. It has now happened to me maybe a dozen times, but certainly is not very common. I have to have just the right amount of fatigue, be on my back in a dim but not totally dark room, and I guess be in the right mental state.
So what do I think this means? My opinion is that when I am asleep, I automatically scan down a column in my visual cortex, perhaps to refresh my visual memory by "looking at" each image in the stack very quickly. This would imply that the images are stored by shape similarity, rather than by semantic content; certainly other brain work seems to agree with this.
Is this the basis for dreams? Humans are very good at organizing sensations into some coherent pattern, in effect creating a "story" that makes sense of what we are experiencing. So if I assume cortical storage is based on shape and not meaning, but my mind tries to make the series of scanned images into something meaningful, I can see where a dream could result. This is not to say that dreams need be random in nature... I can certainly see where my life experience, traumas, relationships, drives, and all that stuff, could have a huge impact on my mental "story-telling". So that even were two people's visual cortex stacked with the same image set, their dreams could be totally different. Still, it is plausible to me.
If anyone else has experienced this type of visual scanning when drifting off to sleep, I'd encourage you to add a comment here. I'd also like to hear from dream researchers.
So what do I think this means? My opinion is that when I am asleep, I automatically scan down a column in my visual cortex, perhaps to refresh my visual memory by "looking at" each image in the stack very quickly. This would imply that the images are stored by shape similarity, rather than by semantic content; certainly other brain work seems to agree with this.
Is this the basis for dreams? Humans are very good at organizing sensations into some coherent pattern, in effect creating a "story" that makes sense of what we are experiencing. So if I assume cortical storage is based on shape and not meaning, but my mind tries to make the series of scanned images into something meaningful, I can see where a dream could result. This is not to say that dreams need be random in nature... I can certainly see where my life experience, traumas, relationships, drives, and all that stuff, could have a huge impact on my mental "story-telling". So that even were two people's visual cortex stacked with the same image set, their dreams could be totally different. Still, it is plausible to me.
If anyone else has experienced this type of visual scanning when drifting off to sleep, I'd encourage you to add a comment here. I'd also like to hear from dream researchers.
# posted by Atrox @ 7:28 AM 
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I have experienced something similar to this. Occasionally when I want to sleep but my brain is too active / unrestful, I get in bed, turn the lights out, and picture a figure-8 ribbon/belt in front of my face, spinning - like the timing belt from a car - as if invisible wheels were spinning it in the loops of the sideways 8. The ribbon is infinitely thin. Where the ribbon crosses itself, just in front of the bridge of my nose is also infinitely small. Following the ribbon with my eyes seems to jump-start the dream-like visuals. Instead of flashes of individual images, what I see is more often a continuous morphing of shapes.
So I think eye movement (even semi-conscious eye movement), visual processing, and interpretation of meaning all feed off of each other, and not necessarily in the order textbooks would suggest. What's near is in the dark, with one's eyes shut, the eye is receiving very little light. Do the eyes "crank up the gain" on a neural level. Or does the visual cortex have a gain of it's own? Could that (noisy) input be one of the drivers / shapers of dreams? If not a function of the actual light (or lack of light), perhaps at least the feedback of the eye's position.
So I think eye movement (even semi-conscious eye movement), visual processing, and interpretation of meaning all feed off of each other, and not necessarily in the order textbooks would suggest. What's near is in the dark, with one's eyes shut, the eye is receiving very little light. Do the eyes "crank up the gain" on a neural level. Or does the visual cortex have a gain of it's own? Could that (noisy) input be one of the drivers / shapers of dreams? If not a function of the actual light (or lack of light), perhaps at least the feedback of the eye's position.
# posted by 
: 10:15 AM
: 10:15 AM
Yes, Evan, mine is also more like continuous morphing than flashing of separate images! It's interesting that you can trigger it with the ribbon trick... I'll have to try that.
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