Psychopaths may come in two varieties.

Some men and women regularly prey on the people around them. Through charm and manipulation, they take what they want and do as they please. Even the vilest acts leave these predators remorseless.

People with this personality, who are known to psychologists as psychopaths, sometimes pay for their deeds by going to jail or psychiatric facilities for criminals. In the August JOURNAL OF ABNORMAL PSYCHOLOGY, researchers report finding that psychopaths who evade the law may constitute a breed apart from those who at some point end up behind bars.

In previous studies, imprisoned psychopaths speaking in front of a camera or performing other stressful tasks expressed little emotion, either verbally or as signaled by increases in heart rate and other bodily measures. They also displayed problems in planning ahead, thinking flexibly, and controlling their impulses.

In the new study, a stressful task induced sharper heart-rate hikes in male psychopaths who had eluded criminal conviction than in their previously convicted counterparts or in nonpsychopathic men, reports a team of psychologists led by Sharon S. Ishikawa and Adrian Raine, both of the University of Southern California in Los Angeles. Moreover, nonconvicted psychopaths scored highest on a test of decision-making skills and impulse control. The three groups scored comparably on an IQ test.

"Heightened physiological reactivity to stress may improve the ability of some psychopaths to evaluate risky situations and make decisions that benefit their criminal careers," Raine says.

The researchers recruited men from five temporary-employment agencies in the Los Angeles area. Participants, aged 21 to 45, were assured that they couldn't be subpoenaed regarding uninvestigated crimes they revealed.

A total of 29 volunteers were identified as psychopaths on a self-report questionnaire. The test probes for characteristics such as superficial charm, frequent lying, shallow emotions, impulsiveness, a need for excitement, and a tendency toward violent outbursts.

Court records showed that 17 of these men had past criminal convictions. Another 26 men recruited from the same agencies weren't psychopaths and had no previous convictions.

Each participant had 2 minutes to prepare a speech detailing his personal faults before presenting it in front of a researcher while being videotaped, a task intended to elicit embarrassment and guilt. During this exercise, non-convicted psychopaths experienced a much greater rise in heart rate than men in the other groups did, the researchers say.

This apparent higher emotional sensitivity to risky situations may also have allowed nonconvicted psychopaths to outscore their peers on a card-sorting task that requires subtle judgments, the researchers add.

"The stress-induced heart-rate rise in nonconvicted psychopaths is a big surprise," remarks psychologist Scott O. Lilienfeld of Emory University in Atlanta. These results don't establish that there are basic differences among psychopaths, Lilienfeld cautions.

It may be that the traits underwriting success in society are the very ones that help some psychopaths evade capture, Lilienfeld speculates. Having the moxie to found and run large companies, for example, would put a smart psychopath in a position to get away with the crimes he or she commits.

Psychologist Robert D. Hare of the University of British Columbia in Vancouver is skeptical of the new findings. Jumps in heart rate could indicate that nonconvicted psychopaths simply tried harder on the speech test and may not reflect differences in their core personality traits, he says.