Philadelphia ? The revulsion of Americans to the recent beheadings of hostages in the Middle East is rooted both in personal horror and cultural aversion.

People react so viscerally to the decapitation executions because they identify strongly with the helpless victims, see the executioners as cruel foreigners, and are horrified by the grisly method of death, Edward Volkman, associate professor of psychiatry at Temple University Hospital and School of Medicine, said.

Volkman said people found dismemberment especially unsettling. They don’t like to contemplate facing an afterlife with head and body separated, he said.

Historically, beheading has been widely used as a form of execution in societies as disparate as ancient Greece, the Roman Empire, England, Germany, Japan, China, and France (where the guillotine was last used in 1977). Among history’s best-known beheading victims are John the Baptist, Anne Boleyn, King Charles I, Sir Walter Raleigh, and Marie Antoinette.

Today, though, beheading is the accepted form of capital punishment only in a few nations, particularly Saudi Arabia, where 53 people were publicly beheaded last year for crimes such as murder, rape and drug trafficking.

The decapitation deaths of kidnapped Americans Daniel Pearl in Pakistan in 2002, Nicholas Berg in Iraq last month, and Paul M. Johnson Jr. in Saudi Arabia on Friday were especially repugnant because they were photographed and displayed worldwide on the Internet.

“The people who are committing these attacks are very sensitive to our sensitivity to this,” Volkman said. “It’s almost like they’re saying, ‘If you really want to tick off Americans … cut somebody’s head off.”‘

Volkman said the deaths seem crueler and more gruesome in part because the victim — and the videotape audience — is forced to anticipate the death.

“Being blown up in a car bombing or shot by a sniper doesn’t carry the same sense of helplessness,” he said.

The killing of Johnson was immediately condemned by Arab nations and Muslim organizations as contrary to the teachings of Islam.

The Council on American-Islamic Relations in Washington called Johnson’s slaying an “act of senseless violence, and (we) repudiate all those who believe such murderous behavior benefits the faith of Islam or the Muslim people.”

The council has launched an online petition drive, called “Not in the Name of Islam,” designed, it said, “to disassociate Islam from the violent acts of a few Muslims.” It said more than 600,000 Muslims have signed the petition.