I was just wondering where or if the brain projects mental pictures. I see them in front of my forehead. Is there where everyone sees them or is it different for everyone?
I can't tell exactly what you mean. It almost sounds like you experience real-seeming visual experiences, images you actually see with your eyes, that are located in space somewhere in front of your forehead.I was just wondering where or if the brain projects mental pictures. I see them in front of my forehead. Is there where everyone sees them or is it different for everyone?
In this case, your brain is making you believe that they are being projected outside. Sounds cool.Sorry I was not more clear. I mean the images of thought. When your eyes are closed. Are those images actaully projected anywhere. Or does my brain just nmake me beleive they are projected in front of me?
I was just wondering where or if the brain projects mental pictures.
Sorry I was not more clear. I mean the images of thought. When your eyes are closed. Are those images actaully projected anywhere. Or does my brain just nmake me beleive they are projected in front of me?
Set the kids loose with the camcorder and the result is always the same: a mad dancing picture as if the scenes had been shot from a particularly hairy fair ground ride. Why can’t they let the camera linger?
As any neurologist knows, the lurching lens is just imitating the child’s saccading eye. Kids naturally expect to be able to shift their attention in eyeball-swivelling leaps three or four times a second and still see a perfectly stable world. So no mystery. Yet in fact the business of saccades remains an especially troublesome one for consciousness theorists.
In the 1990s, the big issue was the binding problem. If the cortex is a hierarchy of processing modules, then how do the various computations get glued together to make a seamless conscious whole? This question has been reasonably well answered with the discovery that coherent firing rhythms help knit widely scattered neurons into fleeting global ensembles. Now mind scientists are asking the same kind of question but concerning the unity of consciousness over seconds rather than milliseconds. The naive view of the brain is that it merely reflects what the sense organs report. Yet if the eyes are skipping from fixation to fixation, then the resulting cortex mappings must leap about like the pictures from the kids’ camcorder. So how can a steady stream of experience be constructed from such violently wrenching foundations?
The need for saccades is clear enough. The cone-dense fovea covers only 1 degree of the visual field. So it’s reckoned that to have foveal level acuity over the whole retina, the brain would need to be hundreds of thousands times bigger and weigh ten tons! Saccading itself is a complex affair. Even when the eyes are fixated, there are constant tremors and microsaccades that keep the retina refreshed. Saccades then come at two rates depending on how habitual or routine the situation happens to be. With highly predictable events, our eyes can flick to the spot in as little as a tenth of a second in an express saccade. For more exploratory looking, it takes a fifth of a second to find a new fixation point.
Of course, during a saccade, retinal output is suppressed to cut down the blur of motion - though recent experiments suggest it is may be rather that the brain immediately forgets any visual input captured while the eye is in transit. But either way, once we count in the 20,000 eyeblinks we make each day, we must be effectively blind about a third of the time!
Actual fixations last around a third of a second. Another recent surprise is that the time the eye lingers is mostly to do with the processing needs of the brain. A visual image can be “snatched” in a tenth of second. But it seems the brain then holds the eye in place largely to give itself grace to complete its processing. So fixation prevents fresh input before the brain is ready.
Change blindness experiments, in which background visual features are sneakily altered while a subject’s eyes are in mid-saccade, raise yet further questions. It used to be thought that vision was stabilised by a simple anticipatory routine. Each planned eye movement generated an efference copy – an exact forward motor projection – that recalibrated the visual cortex, cancelling every apparent jump in the visual scene. But change blindness studies demonstrate that the brain can just gloss over some quite abrupt changes in sensory input. It is only if the background features have been highlighted by prior acts of attention that any changes become detectable – apparently a required part of the forward model.
So how does the brain create a coherent stream of experience out of such restless visual machinery? To cut a long story short, the stability of our mental representations seem the result of a clever mix of rapid forgetting and unconscious prediction. Raw sensory information seems to flow through to the cortex more freely than some older theories suggest. But it is just as freely ignored if it does not fit into a general, expectancy-led, running model of the world. The lurching shifts in visual input are not gated or cancelled out but instead downplayed, rendered vague, as the brain gets on with tracking its own gist-based view of what is happening. So in a neat turnaround, as with the child holding the camcorder, it is the inner narrative which comes first.
The conscious stream – the so-called output – is the foundation for the mental experience. And the wrenching changes in visual input then only get cortically represented to the degree to which they play into the inner tale being told.
The other day, a retired psychology professor told me something startling about himself. He had no mental imagery. Nothing at all. No pictures in the head. No memory for tunes. No ability to imagine bodily actions. Certainly no ability to conjure up a smell or taste.
Once or twice in his life he had experienced the brief flash of a mental image (which is how he came to realise what he was missing). But generally nothing. He couldn't even recall scenes from his childhood or the faces of his family. When I probed him with questions about what he had for breakfast and the colour of his front door, he gave confident answers, but said he still had no pictures in his head. Verbal replies that "seemed right" simply popped into his thoughts.
Of course, he said, no one believes him when he tells them about this lack of imagery. And he was right. I didn't either.
Mental imagery is a tantalising subject; so central to our thought processes and yet so elusive to describe or research. Hundreds of books have been written on the subject. But the explanation that makes the most sense to me was put forward in the 1970s by the Cornell University psychologist, Ulric Neisser. He said imagination was really just sensory anticipation by another name. A mental image is the result of preparing to see or hear or feel something - and then not having the actual thing present to the senses. Memories are used to drive the brain's perceptual apparatus into a state of high expectation, an expectation so vivid that it becomes a surrogate experience.
The brilliance of this explanation is that not only does it tie imagination to something with a clear evolutionary purpose - the general need for brains to predict events in the world - but it also shows why the images themselves might grade from faint inklings and vague premonitions to full-strength, explicit, pictures in the head.
The cortex, with its hierarchical organisation and heavy back-projections between each "rung" of processing, can be driven both ways. The same neural machinery can be driven bottom-up by sensations, or top-down by ideas. As neuroimaging has revealed, picturing a letter or some other target shape can cause a projection of neural activity all the way back down to the primary visual cortex. So the theory goes that the strength of our images depends upon how far back across the sensory hierarchy we manage to push a particular wave of anticipation.
For example, imagine a rhinoceros. That is, ask yourself what it would be like to be just about to see a rhinoceros. You will probably start with a vague feeling of being ready for a rhinoceros type experience - a vigilant, but also oriented, state. Next a concrete image should swim into view. Perhaps a mental snapshot of a dusty-backed rhino standing in the African scrub. You would begin by rousing areas of the temporal lobe with general knowledge about rhinos. Then this would tug on neurons back across the visual pathways until a full-blown image was created.
There is plenty of research to suggest that there is great individual variation in the vividness and stability of such anticipatory images. Some people - like my professor friend - can't seem to get past the initial vague inkling stage. They can't push an expectation to the point where it grows rich in sensory detail. At the other end of the scale, there are those who claim hallucinogenic-strength mental images. These people often have "photographic" memories and are highly hypnotisable. Most of us lie somewhere between these two extremes. Perhaps this natural variation has something to do with the density of a person's cortical back-projections or some other such neurological mechanism.
But regardless, if mental imagery is really anticipation, a basic brain function, then everybody should have imagery of at least the inklings and stirrings kind, even if they might not enjoy full-blown pictures in the head or music in their ears.
My psychology professor admitted this was probably true. When he was answering questions about front doors or breakfasts, he was aware of a background sense of orientation - what he called a state of conceptual-emotive preparation - from out of which the answers sprang. But still, wasn't it surprising that such preparation didn't bear any perceptual fruit at all?
Changing subject, he then told me of a friend who had "kinda fried his brains" on drugs and now claims to see a hundred internal imagery screens at once, all with a different subject and in full colour animation. Well now neither of us knew what to make of the truth of that one.
apeiron said:But the explanation that makes the most sense to me was put forward in the 1970s by the Cornell University psychologist, Ulric Neisser. He said imagination was really just sensory anticipation by another name. A mental image is the result of preparing to see or hear or feel something - and then not having the actual thing present to the senses. Memories are used to drive the brain's perceptual apparatus into a state of high expectation, an expectation so vivid that it becomes a surrogate experience.
If i'm trying to remember something, a formula for instance, I "see" it on the boundaries of my peripheral vision when my eyes are open. When my eyes are closed I can see the image wherever I want, but it usually appears in the position where I first saw the real thing when my eyes were open.
Sometimes I can envision entire scenes while walking around. I look like i'm totally zoned out when I do it and am slightly aware of what's going on around me, but extremely aware of what's going on in my waking dream of sorts... Those are usually brought on when I consider future events, like when trying to figure out the tax of what i'm going to buy at the store before I get there, this triggers a whole scene of me talking to a cashier it's pretty cool, but I don't drive because I zone out too much...
I also get the verbal meaning of the word too (like mentioned in the post above), if it's a sentence the image pops into my head then the sound comes. I have a really hard time copying down the image or explaining it without having a sound attached. I'm always the first one in class to ask "How is that symbol read?"
My attempt at anticipating seeing a rhino lead to a rather quick image of a vivid South African desert with some scrub trees and bushes. The rhino was behind a tree, not visible, and I was waiting for it to walk into view. I don't think that's what you meant.
The process is pretty fast and I couldn't slow it down to observe it.
I think that's pretty strange about the professor who had no mental images. To be clear: he was claiming he had no interior monolog as well?
Makes sense.thanks for the articles. Very interesting and well written. I just realised that my mental images are not only infront of my forehead. They are everywhere my eyes look. I just tend to look up when I close my eyes hence the image being there.
I wonder if you saw any Kluver "Form Constants":Interesting that you mentioned drugs aswell. I did mushrroms a few times when I was younger and the things I saw when I closed my eyes were so strange that I could not beleive they were coming from my own brain. But I assume that is my brain miss firing so I percieve very random images of lots of things combined to form new strange things.