International Game Technology, the nation's top slot machine manufacturer, employs no psychological tricks in its efforts to "make our machines exciting and fun," insists Connie Jones, the company's director of responsible gaming.

But some researchers view slots as the most addictive type of gambling there is. It's repetitious and fast. The lights and sounds can be hypnotic. And people can be so lured by the near misses that come up, almost delivering big jackpots, that they lose track of the actual likelihood of winning.

"Any form of gambling is potentially addictive, but [slots] tend to be more addictive," said Nigel Turner, of the Centre for Addiction and Mental Health in Toronto.

"There's no stop, like buying a lottery ticket. ... Slots tend to be the game format most frequently associated with help line calls, in part because they're the most widely available continuous games out there."

With so many nonaddicts enjoying slot machines as entertainment, it can be hard to tell where the line is drawn between the pleasure described by Ms. Jones and the pain referred to by Dr. Turner.

When Pennsylvania passed its 2004 slots law, it determined its casinos would have no table games, only slots. No official reason was given, but the explanation most common since then was that it enhanced the prospects for positive votes from lawmakers wary of gambling.

Legislators have discussed allowing table games as part of resolving this year's budget gap. Regardless, the state has already allowed more than 30,000 machines that might be far worse for potential addicts than table games. The machines have wide appeal to nonaddicts as well, judging by how they usually represent more than two-thirds of revenue at casinos that include table games.

The machines require no skill. Players have little influence on the outcome, which is determined by a random number generator constantly spinning inside the machine. With the right design, they draw players even though most understand that it's much harder to win than lose.

Researchers say compulsive gamblers, however, frequently fail to take into account the true chance of winning. They end up spending far more proportionally than the average casino visitor.

Various studies have suggested that problem gamblers represent one-fifth or one-fourth or more of casino revenue, even though only 1 percent of people are identified usually as pathological gamblers and another 2 percent to 3 percent fall into the "problem" category.

"Anyone that plays slots heavily or frequently, there's a good chance they're a problem gambler and contribute a disproportionate share of revenue," said Garry Smith, a gambling research specialist for the Alberta Gaming Research Institute.

"People who become problem gamblers are often unhappy with their life circumstances, and so play the machines to escape," he said. "It's a form of medicating themselves that works for a while. They do zone out when playing the machines for a while, go into a kind of trance, feel better about themselves.

"Once in a while, they win a jackpot, and people look at them and recognize them and they get social rewards they don't otherwise get. But obviously, it's a poor way of coping with the problems, because it's not doing anything to face their basic problems, and now they're losing money too."

Canadian provinces have both casinos and legal slot machines elsewhere, such as in bars and truck stops. Researchers view the "convenience" gambling in neighborhoods as even worse for potential addicts than casinos. But the provincial governments, which own the machines, also typically put more effort than U.S. states into problem gaming strategies.

On machines outside casinos, provincial governments have begun using techniques such as pop-ups on the game screens to remind people how long they've been playing. Nova Scotia is testing a system in which players swipe cards that personalize the machines to their preset specifications, such as limits on how much they can play and spend.

Bob Breen, director of the Rhode Island Gambling Treatment Program, said that of about 1,000 individuals the program has treated, nearly 70 percent of them are addicted to video gambling machines of some form. Those players frequently become addicted in less than a year, far quicker than those succumbing from any other form of gambling, he said.

Mark Griffiths, professor of gambling studies at Nottingham Trent University in England, said game designers are ingenious at softening the blow for players losing money, such as by using a humorous character's catch phrase from "The Simpsons."

Research has also shown that people are tantalized, rather than repelled, by a certain number of times they come close to a jackpot, Dr. Griffiths said. Designers make use of that, he said, realizing that people can enjoy coming close as much as 40 percent of the time, but get too frustrated if it's more often.

"People not only get a physiological buzz when they win, but also when they nearly win as well," he said.

U.S. casinos and state regulators who oversee them have not sought anti-addictive features on the machines.

"Government is often conflicted on gambling issues, partly because it can become a very important revenue source, as it has in Pennsylvania," noted Bill Eadington, an economics professor and director of the Institute for the Study of Gambling and Commercial Gaming at the University of Nevada, Reno.

Ms. Jones, of IGT, said it's up to the casino operators or regulators -- not the company's game designers -- to impose any features that might offset compulsive gambling. But thus far, she maintained, there's no evidence such restrictions actually curb abuse.

"The things we do to make our machines exciting and fun, some view as making them more addictive. That's certainly not our intent," she said. "Our game designers don't even think about addiction -- they think about beating Bally's and other competitors. They're creative folks who want machines to create the most revenue."