Capgras delusion or Capgras syndrome is a psychiatric disorder in which a person holds a delusion that a friend, spouse, parent, another close family member, or pet has been replaced by an identical impostor.[a] It is named after Joseph Capgras (1873–1950), the French psychiatrist who first described the disorder.
In a 1990 paper published in the British Journal of Psychiatry, psychologists Hadyn Ellis and Andy Young hypothesized that patients with Capgras delusion may have a “mirror image” or double dissociation of prosopagnosia, in that their conscious ability to recognize faces was intact, but they might have damage to the system which produces the automatic emotional arousal to familiar faces.[21] This might lead to the experience of recognizing someone while feeling something was not “quite right” about them. In 1997, Ellis and his colleagues published a study of five patients with Capgras delusion (all diagnosed with schizophrenia) and confirmed that although they could consciously recognize the faces, they did not show the normal automatic emotional arousal response.[22] The same low level of autonomic response was shown in the presence of strangers. Young (2008) has theorized that this means that patients with the disease experience a “loss” of familiarity, not a “lack” of it.[23] Further evidence for this explanation comes from other studies measuring galvanic skin responses (GSR) to faces. A patient with Capgras delusion showed reduced GSRs to faces in spite of normal face recognition.[24] This theory for the causes of Capgras delusion was summarised in Trends in Cognitive Sciences in 2001.[2]
I don’t know about favorite, but high on the mess-with-the-head factor.
https://en.wikipedia.org/wiki/Capgras_delusion
There’s another interesting rabbit-hole.