If you walk around the river houses on a Saturday night, students say, you can smell the odor of marijuana wafting through the air.

But despite a recent study showing that heavy marijuana use impairs test scores, some students say they will continue to smoke up--primarily for social reasons.

A study released last week by three researchers at McLean Hospital, a Harvard-affiliated hospital, shows that college students who smoke marijuana heavily suffer from a decrease in cognitive abilities--even 24 hours after having last used the drug.

The study compared students who use marijuana an average of 29 days per month to light smokers who use the drug one or two days a month. On tests measuring verbal and attention skills, the heavier users fared worse than the lighter users, according to a press release.

The researchers attributed the poor scores mainly to impairment of one's attention span.

But some students say they do not believe the study's conclusions and will continue to smoke without fear.

One senior in Currier House who considers himself an occasional smoker says he enjoys smoking marijuana because he likes the feeling.

"I feel sort of light, like I'm floating," he says.

The senior says he knows several Harvard students who are heavy users but who do not appear to have decreased cognitive skills as a result of their drug use.

"You can still think relatively coherently [after using marijuana]," he says.

Marijuana tends to affect motivation rather than cognition, the Currier senior says.

"The people who are smoking it a lot, while they are smoking, tend to be lazy about things," he says.

But these heavy users are not lazy about continuing to smoke up, he adds.

Other students charge that even light marijuana use can impair cognitive abilities.

An Ivy Yard first year who spoke on condition of anonymity says she believes even light marijuana use can cause cognitive impairment.

"Smoking a lot affects the way you act," she says. "Your mentality changes when you smoke up a lot; you're used to being high."

Recounting her own experiences with marijuana, she attributes this decreased acuity to feeling high.

"You definitely feel more relaxed [and] everything's definitely more hazy," she says. "You don't have clear thoughts and it's harder for you to speak sometimes.

The student, who considers herself a former occasional smoker, says inhaling marijuana also can impair one's control.

"I have driven while I was high and it definitely does [have an effect]," she says. "You don't have as much control; your ability to register things is much lower."

Another smoker--a sophomore in DeWolfe--says heavy marijuana users do not speak coherently.

"You can tell people who are on it from their speech patterns and what they say," she says. "If they smoke a lot, they talk slower. It's just like they're really mellow all the time."

The student--who says she smoked marijuana for the first time last year with acquaintances who lived in Quincy House--says watching heavy smokers convinced her to inhale only nine times.

"I didn't want to become a pot head like my friends," she says. "Ten and up is just a problem, you start losing track [of how much you've smoked]."