ps418

Capgras' Delusion is a delusional disorder in which someone becomes convinced that their close relatives have been replaced by an imposter or robot or otherwise exact double. Recognition is not impaired -- yet the person is totally convinced that their familiars, usually parents or spouse, are not really who they appear to be. It occurs in the context of some psychiatric illnesses, and has also been triggered by brain trauma and organic brain disorders.

Prosopagnosia, on the other hand, is a condition characterized by an inability to recognize faces, usually as a result of occipito-temporal brain damage. It is unrelated to visual ability or mental illness, and is thought to be caused by a disruption of a specific brain circuit that specializes in face recognition (yes, there is such as thing. See Haxby, 2001). Propoagnosiacs can recognize you just fine by voice though.

There is an interesting difference between these two disorders. Although genuinely unable to consciously to recognize face, prosopagnosiacs can display a form of <a href="http://www.columbia.edu/cu/psychology/courses/1010/mangels/CovertProso.pdf" target="_blank">covert recognition</a>. For instance, if you show a series of familiar and unfamiliar faces to a prosoagnosiac, and measure their skin conduction response to those faces (a measure of autonomic arousal), they will show a higher amplitude response to the familiar faces than to faces of strangers. Their brain knows the difference, but they do not consciously know the difference.

Capras' Delusion sufferers, on the other hand, show little differential SCR response to familiar faces, even spouses and parents. They do not have a larger SCR to familiar faces. The graph below, from Ellis, shows the difference in SCRs. The delusion is probably generated in an attempt to "disambiguate" the strange lack of feeling, which they had hitherto always felt when seeing their loved ones' faces.



When I read this, I wondered: Assuming one believed in a soul and an afterlife complete with deceased relatives' souls, would the Capgras' delusion person suddenly regain recognition, or would they think that the spirits were imposters?

. . . ok, its a stupid question.

Patrick

<a href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=112872 68&dopt=Abstract" target="_blank">Capgras delusion: a window on face recognition. Trends Cogn Sci 2001 Apr 1;5(4):149-156</a>


<a href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=108274 45&dopt=Abstract" target="_blank">Haxby et al., The distributed human neural system for face perception. Trends Cogn Sci. 2000 Jun;4(6):223-233.</a>

thebeave

I saw a TV special a few years ago about a guy who had this disorder. It was one of the oddest things I ever saw. It was a young man who suffered a specific brain injury in some kind of accident, as I recall. He lived with his mother (or was it his wife?), and he absolutely 100% would not believe that was really her. He was convinced she was an exact duplicate lookalike, but that there was no way he said it could be his real mother. Everything else about his behavior seemed normal. Eventually he seemed to adjust to the idea of living with this "imposter", but wouldn't accept her as real. Doctors traced the problem to some tiny area of damage in his brain. Can't remember if they were able to make him normal again or not. Bizzarre!

cricket

It is weird; what are they thinking? The 'impostor' not only looks like the loved one, but also wants to live with the capgras sufferer! What a coincidence!

Jesse

It's also weird that even after they're told that it's a well-known neurological condition called "Capgra's delusion" they can't learn to consciously ignore the fact that loved ones look unfamiliar to them. Does the condition interfere with general reasoning abilities? Maybe some do learn to ignore it, and you just don't hear about them as much (and maybe these people would no longer be identified as suffering from the 'delusion' even though familiar faces would continue to look strange).

I wonder what happens when people with this delusion look at pictures of famous strangers like celebrities, or even famous faces in art like the Mona Lisa. Also, does their own mirror image look like a stranger to them?

[ December 10, 2002: Message edited by: Jesse ]</p>

Jay30

This may be the program you are referring to, beave:

<a href="http://www.pbs.org/wgbh/nova/transcripts/2812mind.html" target="_blank">Nova: Secrets of the Mind</a>

The story of David, the one with Capgras' Delusion is about halfway down. Very interesting story, you would almost think he was joking. Gladly, the condition eventually went away in his case.

Jay

thebeave

That's the one I saw! It's funny how adamant people get that their brain is always 100% accurate about the outside world, despite the absurdity of their belief. It's no wonder people are so easily prone to believing that ghosts, aliens, angels, etc are real.

Gurdur

General reasoning abilities are already no longer optimal in Capgras'; often, Capgras is the result of neurological damage.

You over-estimate the power of reasoning over what is basically hard-wired stuff.

Part of what I wrote for my formal debate with Metacrock:
Edited because of ever-changing internet and dead links.

[ December 10, 2002: Message edited by: Gurdur ]</p>

Jesse

Gurdur:
You over-estimate the power of reasoning over what is basically hard-wired stuff.

I wasn't saying that reasoning could override the fact that people looked unfamiliar, just that one could learn to accept that these people really are the people you used to know, and therefore learn to treat them as such, even if their faces continue look totally wrong. After all, neurologically normal people can come to convince themselves that their dogs are "really" reincarnations of deceased relatives (I saw such a woman on Jay Leno once), so this doesn't seem much harder.

But, if overall reasoning is significantly impaired, perhaps this sort of ignoring of what your senses are telling you wouldn't work.

[ December 10, 2002: Message edited by: Jesse ]</p>

Gurdur

No, you don't see the problem; let's assume a brain area for recognising people near to one, and a dedicated connection with the face-recognising area. Something goes blooey in the wiring.
How do you compensate for that ?
You simpy don't feel the connection or recognition, so you can't really accept it.

Allow two examples:
a very simple defect in the proprioceptive system can lead you to believe that your right leg no longer belongs to you.
Note all the rest of you is OK - including all your reasoning power.

No matter how many times someone tells you "It's your right leg", you won't believe them - since it's no longer included in your automatic body schema, and therefore feels completely foreign.

Another example: a particular aphasia (as, say, the result of a very small stroke in a very small area) can lead you to completely lose access to tghe word "pencil" in your vocabulary.
You can describe it, you can describe what it is for, but you can't utter the word "pencil" - even though someone repeats it to you.
Note cognition is unimpaired.

These are every-day clinical examples (at least the second one is, the first is a bit rarer).
Much more of our "consciousness" is automatic ("instinctual") and hard-wired than we like to think.

Jesse

Gurdur:
No, you don't see the problem; let's assume a brain area for recognising people near to one, and a dedicated connection with the face-recognising area. Something goes blooey in the wiring.
How do you compensate for that ?
You simpy don't feel the connection or recognition, so you can't really accept it.

I still don't see why it would be impossible. Imagine I'm in a VR simulation with my friend, and although in reality she's a 22-year-old woman in the simulation she looks like a 45-year-old-man; I wouldn't feel any connection to this face either, but I could still intellectually recognize who it really is and treat them accordingly.

If a cognitively normal person with this condition just found it too disconcerting to look at people and have them appear "wrong", he could always adopt strategies like not looking directly at people when talking to them--recognition of voice is not affected, right? I think it is possible, to some extent at least, to compensate intellectually for distorted senses--consider the difference between drugs which create vivid hallucinations which the user knows are not real, and drugs which impair judgement so the user is actually delusional and can't tell hallucinations apart from reality (likewise, consider the difference between ordinary dreams and lucid dreams). Or consider the story of John Nash, who says that he continues to hear voices on occasion but has learned to ignore him (although I'm sure there has been an organic change here as well).

[ December 10, 2002: Message edited by: Jesse ]</p>