tenpastmidnight blog

Making hay while the sun shines

Split-brain

My cousin Michael is moving his forums, 'Digitalaudience' and the database of previous posts isn't going with it. For posterity here's my most useful post, dating from 8th Sept 2003:


Severing the corpus callosum, the main connection between the two halves of the brain, is still used as a treatment for very severe epilepsy, though usually only if it is life threatening. It is an effective treatment for these extreme cases because it stops the chaotic activity of the fit spreading from one hemisphere to the other. This stops it feeding back and forth between the two sides of the brain, breaking the loop and keeping it to a less severe form.

It's a very drastic procedure (if you're interested in how they do it it's worth seeing a video, but you need to have a strong stomach) and can have some side effects, though oddly most are not noticeable to other people and only come up in psychological tests looking for the effects of the operation. The strangest side-effect is usually only temporary and is called the 'alien hand' syndrome, where one hand will try and interfere with what the other is doing.

In the case I remember about this, a woman who'd had the operation to split her brain was having trouble afterwards with one of her hands. If she was loading the washing machine, her hand (I think it was her left) would pull the washing out as her right was putting it in. If she got out of the swimming pool and someone handed her a towel, her right hand would take it and her left snatch it and throw it in the pool. Not only was this quite disturbing, she was getting fed up with having to shove the washing in the machine quickly and run away from it before her other hand could take it out or fiddle with the controls.

Usually, this effect is very short lived, and AFAIR she did eventually get over this. It turned out the effect only happened when it was a one-handed task and seemed to be her other hand trying to help out, but that side of her brain didn't know what was going on so was messing things up. When she did something that took both hands, e.g. driving, it was fine.

Very odd.

For some tasks, like finding an odd-one-out element in a field of something similar, people with split-brains are actually quicker than those of us with a normal brain. So, if they had to look for a colon in a load of semi-colons like this:

; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; : ;
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ;


They'd find it quicker than you (unless you happen to have a split-brain.) Because both sides of the brain can concentrate on slightly different parts of the overall field. NB: This doesn't mean the different sides of the brain look out of different eyes. The right side of your brain receives messages from the left side of both of your eyes, and the left side of the brain receives the stuff you're seeing on the right side of your eyes. So if you look directly at a vertical line on your screen, the left and right sides of that line go to the opposite sides of your brain.

There's stuff from the perspective of someone who's had the op. here: World view from a split-brain perspective
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