An article from Canoe Canada News today includes a brief explanation of the manifestation of Capgras Syndrome. (see the previous posting, on Tony Rosato and his situation).
"People identify one another in various ways - through appearance, voice, mannerisms and the way they relate to others. When those characteristics change, a healthy person can conclude it's not because the person has been replaced by a doppelganger, Jeffries [Dr. Joel Jeffries, a psychiatrist at the Centre for Addiction and Mental Health in Toronto] said.
"What happens (with Capgras) is that that capacity gets impaired, though we don't know how," he said.
People diagnosed with the delusion are usually more annoyed than angered by the perceived change, he added.
"They'll usually ask, 'Why are you doing this?' or 'What happened to the real people?"' Jeffries said. "There's often annoyance, more than alarm."
A psychiatrist in the United States wrote about one Capgras patient who thought his poodle had been replaced by an identical but different dog. Another study cited a patient who, every morning, believed that his running shoes had been replaced by identical substitutes during the night.
Jeffries said patients usually respond to treatment with anti-psychotic medication. He said he wasn't aware of a case where, with appropriate treatment, a patient was unable to shake the delusion.
"I'm sure it happens, but it's relatively rare that the belief becomes intractable.""