Monday, 20 February 2012
The woman, referred to as J.S., struggled to recognise family, fared slightly better with celebrities, whilst having no problems correctly categorising as unfamiliar the faces of complete strangers. When the woman's daughters came to visit her in hospital, she had no trouble recognising the daughter she hadn't seen for eight years, but struggled to identify her other daughter who visited daily.
Joost Heutink and his team confirmed this pattern of deficits by comparing J.S.'s performance against three age-matched women in a series of face recognition tasks. As well as having impaired recognition of her family (and to a lesser extent celebrities), J.S. also reported that the appearance of her family members was distorted. For example, she said her grandchildren looked grossly overweight and that they were a deep tanned colour. J.S. also had a general problem recognising emotional facial expressions.
Further details came from recordings of J.S.'s skin conductance (a measure of physiological arousal) when she looked at various faces. This showed that she experienced more arousal after looking at family members' faces as opposed to strangers and celebrities. This is normal, although the peak and latency of this arousal was delayed relative to the control participants.
So what explains J.S.'s pattern of deficits? Those familiar with neuropsychology may be reminded of Capgras Syndrome, in which the patient claims that one or more close relations have been replaced by an imposter. But J.S. does not have this syndrome. People with Capgras say that the imposter is a perfect likeness to the real relation. By contrast, J.S. does not think her relations are imposters, she just struggles to identify them and thinks their appearance has been distorted.
J.S.'s condition also bears some resemblance to prosopagnosia - a specific deficit affecting face recognition. Again, this doesn't really match J.S.'s neuropsychological profile. After all, her recognition of strangers' faces as unfamiliar was near perfect. Moreover, the brain region that's normally damaged in proposopagnosia - the fusiform face area - was unaffected in J.S.'s brain.
Joost Heutink and his colleagues think part of the answer may lie with a rare condition known as prosopometamorphopsia - in which other people's faces are perceived as being warped or distorted. The researchers suggest J.S. may have a form of this condition that interacts in some way with the emotional meaning of faces. So, if a face affects her emotionally (as happens with family), she perceives their face as distorted, which also has the side-effect of affecting her conscious recognition. This account fits with the distribution of brain damage in J.S.'s brain. In particular she suffered damage to the posterior superior temporal sulcus, which it's been suggested is involved in merging information about face identity with emotional context and meaning.
This account also helps explain two exceptions to J.S.'s relatively superior performance in recognising celebrity faces vs. family members. When it came to images of Hitler and Bin Laden (characters likely to trigger an emotional response), she believed they actually depicted imposters, and poor ones at that.
Heutink, J., Brouwer, W., Kums, E., Young, A., and Bouma, A. (2012). When family looks strange and strangers look normal: A case of impaired face perception and recognition after stroke. Neurocase, 18 (1), 39-49 DOI: 10.1080/13554794.2010.547510
Post written by Christian Jarrett for the BPS Research Digest.