The study is skewed.
Only dumb stupid people can form a dependancy on pot.... or mental dependancy. Why? Coz pot is by no means an addictive drug like crack. There is no true "pot addict" in a chemical sense like heroin, cocaine, nicotine, alcohol, morphine...etc.
So for those who form a "habitual" or "mental" dependancy on pot....are people who were stupid to begin with :
high school drop outs who only want to keep smoking pot, low self esteem, lazy, don\'t care to learn anything, too dumb and lazy to hold a job long enough......
so yeah, with or without pot use, they would have flunked those memory tests anyway. Considering their lack of interest in a lot of things.