Erm, define "impairment". Yes this study notes reduced performance in some areas (but the authors acknowledge plenty of weaknesses and explanations in their discussion). However, increases in something like "creativity" might reduce e.g. verbal fluency, while increasing "performance" for artists, or increasing insights when problem solving in many disciplines.
Well, to look for impairment at any specific task, you want to just do that task, of course.
I agree there's really no meaningful concept of "general impairment" unless you're talking about something more extreme like a brain disorder or heavy alcohol intoxication with global involvement leading to something like a coma or gross movement disorder.
These various neuropsych tests try to test something as specific as possible. Working memory for instance. Their development is a complicated field all on its own. And this is psychology, so it's good to keep the reproducibility crisis in mind and adjust one's credences accordingly.
There's a really cool painter whose name I forget who mainly does self portraits while under the effect of various substances. The one where he huffed computer duster for instance,is just a few meaningless lines on a mostly white canvas. That's a pretty good example of global impairment right there. And there's also sorts of paintings on psychedelics, showing varying degrees of visual impairment. Really recommend googling the guy if you want a very visceral way of visualising the various impairments brought on by psychoactive drugs.
This is becoming an unfocused rant so I'll cap it off here I guess.
There are definitively a number of artists that say they work better with alcohol. "impairment" would be defined as something that increase risk of reduce performance, as in, people who drink alcohol has a higher risk of having their driving skill reduced compared to those who don't have alcohol in their blood. Such statement doesn't exclude the possibility that alcohol may increase driving ability compared to base line, only that the variance is higher and thus risk.
