Explanation: Chemicals
There are four primary chemicals in the brain that effect happiness: dopamine, oxytocin, serotonin, and endorphins. By designing gamified experiences that activate these chemicals, you can increase your users' happiness and loyalty.
The human brain has up to 100 billion neurons (nerve cells)
Technically, all of these can cause double vision and other vision problems.
I'm not really sure what "less responsive" indicates, because it can mean a broad spectrum of symptoms. However, I would answer this with alcohol because it causes your eye muscles to weaken and can include symptoms like involuntary twitching.
Sorry I couldn't provide you with a definite answer, but I hope I was able to help :)
