There are certain cognitive abilities that improve with practice. You'll find that you can get faster at most things you practice if you're able to do them already. A well known example is games like "Brian Age" on the Nintendo DS and Wii. If you play them often you will definitely see improvements on your performance in the exercises in the game, however not in general, as has been recently proven [1].
Intuitively I'd say that your cognitive ability isn't (to put things simple) a value but a range, and you can train yourself by studying to be higher within your range. I believe there are actual physical barriers that don't allow you to push over your "range" - or we'd see obsessed people turning into Savants.
(Regarding your marijuana point: I have seen the impact of daily pot smoking on friends, and it is quite real. I have also seen the effect go away when they stopped smoking. Sounds like a cliché out of a book on morals, but it is the truth)
I read an article a while back talking about how games like that don't boost the brain's overall ability to think and reason quickly in general, they just improve your brain's performance on those games. That is to say, you're not getting smarter or faster, you're just getting better at Brain Age.
(I have the link handy because I was looking it up yesterday for my DNB FAQ http://www.gwern.net/N-back FAQ.html - DNB being one of the few brain games which apparently does transfer/improve 'in general'.)
(Regarding your marijuana point: I have seen the impact of daily pot smoking on friends, and it is quite real. I have also seen the effect go away when they stopped smoking. Sounds like a cliché out of a book on morals, but it is the truth
Hi fredoliveira
Would you mind elaborating on this a little? It's an area of personal interest. Only for scientific reasons of course ;)
I can try :-) I am no doctor so everything I'll say is based on what I've seen and personal opinion, so take it with a grain of salt.
A close friend who went to the same university as I did smoked every single day for as long as I (and most people) can remember. He was considered "dumb" - writing this now sounds like people around him were assholes, which isn't the case; we were indeed all friends. He did score poorer grades than the rest, and had severe mood-swings.
A few months ago, he decided to stop smoking pot. I cannot begin to tell you how different things felt. His performance has apparently increased dramatically (to the point where he's now over the group average) and the mood swings are gone. Interestingly, the mood didn't improve for the better and he might be going through depression. But despite the psychological downturn (which may have other causes), his cognitive abilities have noticeably improved.
Again, I'm no doctor, so I can't say for sure whether the two things (stop smoking pot <-> better mental performance) are connected. But as with most people, my gut tells me it is. Just thinking about the people I know who smoke every day, I realize that my expectations for them are lower. Again, by writing this I feel like an ass - I am just being honest, though.
I have heard the same thing. Someone I know smokes rarely, but he plays chess online quite often. He tells me after every time he smokes (probably just one or two joints) his performance is noticeably worse for a week after. And this is from someone who just smokes maybe once a month if at all, daily smoking could impair your cognitive abilities a lot more. But then again this is all more or less anecdotes, still seems to be something about it though.
Marijuana doesn't make you dumb permanently... Alcohol has far worse effects on the brain than marijuana, especially over the long term. Listen to Dr. Drew, he says it all the time.
The last few studies I've seen on moderate alcohol use have concluded that its short-term effects on the brain aren't necessarily cumulative over the long term, as opposed to conventional wisdom.
By the same token, is there any reason to assume that someone who uses marijuana doesn't drink irresponsibly too? While I was in college, the two seemed pretty inseparable on average.
I think he's means it as in compare it to someone who's stoned day in day out for X years, and then decides to quit and then their mental function returns to normal. Compare those two differences. Actually I don't think what he says contradicts anything you're saying.
also, can you train yourself to be smarter by forcing yourself into such a state, much like weight training or high altitude training?