A "SEXUAL tsunami" is how Mary Anne Layden describes the abundance of pornography the Internet has enabled. She believes that this pornography is qualitatively and quantitatively different from any that has come before. That, she says, makes it a public- health problem.

This tsunami has swamped Pennsylvania, in the form of Porngate, the revelation that highly placed officials in the Attorney General's Office and elsewhere were exchanging pornographic emails - in the hundreds.

Supreme Court Justice Seamus McCaffery resigned over the revelation that he participated, and a handful of prosecutors were fired. Last month, the court released some of those emails, revealing the full extent of their crudity, explicitness and volume.

Many were sent by former prosecutor Frank Fina, who now works for Philadelphia District Attorney Seth Williams. Last week, Williams gave Fina and two others - Marc Costanzo and Pat Blessington - a pass for their participation.

We sought out Layden to help us understand the implications of this behavior. She is a psychotherapist, the director of education and the director of the Sexual Trauma and Psychopathology Program at the Center for Cognitive Therapy at the University of Pennsylvania. She specializes in the treatment of victims and perpetrators of sexual violence, sexual addicts and sexual exploitation. She has testified before the U.S. Congress and lectures extensively. Here's what she had to say:

Q: You have referred to the Internet as allowing a sexual tsunami of porn. Why is this a problem?

A: First, we're telling women "your worth is based on your sexual attractiveness," on whether men would choose you for sex. The message porn conveys - for example, that all women like anal sex, or women like being raped - is miseducation about sex, and in fact it's often the only sex ed young people are getting. Young men are pornified, college students are porn-ready. Porn tells them their sexual appetite doesn't have to be controlled, that there's no such thing as too much sex. They're thrilled with that message. Porn has contaminated the whole society.

Q: What does the research tell us about men who use porn?

A: What we find is that the damage moves along a continuum; for example, at the light end of damage, those who use this material are more likely to be sexually callous, less supportive of women's rights, more likely to judge their partners' sexual behavior and their appearance (i.e., why doesn't she act like a porn star, or why doesn't she look like Barbie?).

In the middle range of damage from porn use, they start to interact better with pixels than with people, and we see high rates of erectile dysfunction when they're with women, even in men as young as 25.

Brain research finds that in those who view porn, the impulsive part of the brain is more engaged - what I call "teen brain"- and the rational part of the brain is less active. These men are less likely to expect themselves to be faithful when they are married and are more likely to cheat.

They also believe that rapists deserve less time in prison, are more accepting of the "rape myth."

At the heavy end of the spectrum of damage, men are more prone to sexual violence, acquaintance rape, child molestation and assault. They're more prone to engage in sexual harassment on the job and more likely to be attracted to 13 or 14 year olds.

College men exposed porn are more likely to have engaged in nonconsensual sex.

Q: In Porngate, a large group of men were exchanging explicit emails in a workplace setting. Is this use of porn as a shared experience a cause for alarm?

A: I see a number of alarms: Porn has now been normalized in this society, and that's massively troubling on a psychological level.

When I'm treating sex and porn addicts, many of them are in jobs with zero tolerance for the use of this material on their jobs, and yet they still access it; there is something amiss in their decision-making abilities.

When a group is involved, there's a permission-giving belief, the thought that "everybody's doing it, it must not hurt anyone. It must be OK."

They start to normalize it, give themselves permission to do it, can't figure out why people are upset.

These guys are telling each other this is fine. But you know, in a more extreme example, pedophiles get on the Internet and tell each other how normal it is. It's a complete distortion, which they encourage in each other.

Q: Is pornography addictive?

A: I treat porn addicts. What's common is denial that it's a problem even in the face of evidence that it has damaged their life, and escalating behavior - you must access more material and more explicit material to gain the same level of satisfaction - those are all pieces that tell us it's an addiction.

Brain studies map the pathway of the centers of the brain that are engaged when drugs are used; it's the same pathway used when you're using porn. The first study was not meant to measure effects of porn, but to study cocaine addicts. Coke addicts were shown images of people using cocaine and parts of their brains lit up; the same areas of the brain lit up when subjects who were not addicted to anything (including porn) were shown porn.

Q: Some of the men we're talking about in the Attorney General's Office were working on the Sandusky case, or other sex crimes. Could this make them more "immune" or desensitized to the kind of explicit images found in the emails?

A: Exposure to porn changes your attitude toward porn and toward sexual violence. Exposure to porn makes men reduce their judgment that the material is even pornographic.

In addition, summaries of research find that adult males exposed to pornography are more likely to believe women in general enjoy rape, are more accepting of violence against women and are more likely to engage in sexual harassment behaviors.

I don't think the Sandusky case involved images that people were forced to look at. However, if looking at porn elsewhere increases the sexual attraction to minors, what does looking at porn do to those who are charged with investigating and prosecuting others who are attracted to minors?

Q: People argue that porn is not illegal, and is protected by the First Amendment.

A: In the United States, federal law makes it illegal to produce and distribute obscenity and the Supreme Court has found that the First Amendment does not protect obscenity. The production and distribution of obscenity is against the law.

At the federal level, the Department of Justice child exploitation and obscenity section has prosecuted cases of child exploitation and obscenity, although four years ago the obscenity prosecution team was disbanded. People who are sending you emails may be distributing obscene material. That may be breaking federal law. This is not normal.