Las Vegas casinos have long played to the senses. They're virtually synonymous with the sound of jingling coins, the taste of free-flowing alcohol, the sight of glittering lights and the touch of forearms on green felt-covered tables.

And the sense of smell? If anything, casinos are known for the scent of cigarette smoke, Aqua Velva men and Aqua Net women.

That could change. A study by Chicago researcher Dr. Alan Hirsch found that Las Vegas Hilton gamblers dropped 45.1% more coins into slot machines in an area that was scented with a pleasant odor.

What's more, dollar figures supplied to Hirsch by the Hilton showed that the slot machines in fragrance-free areas had no decrease in revenues.

That finding, says Hirsch, is important because it suggests that the pleasant odor did not draw gamblers away from other areas. Rather, it appears to have encouraged gamblers in the scented area to continue inserting coins for longer periods than usual.

Hirsch, a psychiatrist and neurologist who is an assistant clinical professor of neurology at the University of Illinois, won't say what particular odor created the change in income. He'll only say that the smell has received the Food and Drug Administration's GRAS (generally recognized as safe) rating and is a "blend with no well-defined high notes."

He's not sure why the fragrance increased gambling. But he speculates that it may have made people more alert or more relaxed--or it may also have worked by inducing "olfactory-invoked nostalgia," the way smelling fresh-cut grass sometimes reminds people of their childhoods.

Although Hirsch doesn't know why the odor worked, he does know that higher concentrations of it were more effective than lower ones, a significant finding in that critics of scented environments fear that fragrances may be used subliminally to manipulate behavior.

Says Hirsch: "We have done tests in the past where we found we could actually affect brain-wave frequency with odors in such low concentrations that they could not be detected, but I think it's really unethical for a retailer or any sort of merchant to use odors subliminally." He adds that odors used in the Hilton study were strong enough for patrons to detect.

The study was conceived and funded by the Smell & Taste Treatment and Research Foundation in Chicago, an organization founded by Hirsch.