means growing up unable to recognize faces, including famous ones and sometimes close family. Whether anything is working underneath has been argued about for years, mostly from behavior. So 12 people with the condition judged famous and non-famous faces as familiar or not, with electroencephalography running throughout. The interesting trials are the failures. What does the brain do when the person says they do not know a face?
Part of the recognition fires anyway. In six of the 12 participants, famous faces they had failed to recognize still triggered an occipito-temporal , the component thought to reflect activation of for known individual faces. The , tied to the later semantic stages of identity processing, did not fire for those faces. The visual trace was intact and the link onward was not.
Developmental prosopagnosia is a lifelong difficulty recognizing faces that arrives without any brain injury. People with it can fail to place famous faces and sometimes relatives. Whether some recognition survives below awareness, called covert recognition, had been argued mostly from behavior and never settled neurophysiologically.
The design is simple and well aimed. Twelve participants with developmental prosopagnosia judged the familiarity of famous and non-famous faces presented one after another, while electroencephalography recorded throughout. Event-related brain potentials were then computed separately for recognized famous faces, non-recognized famous faces and non-famous faces.
In six of the participants, famous faces they had failed to recognize nonetheless triggered an occipito-temporal N250, the component thought to reflect activation of a stored visual memory of a known individual. The P600f, linked to late semantic stages of face identity processing, was not triggered by those same faces.
On the few trials where participants did classify a famous face as familiar, the potentials looked like those of people with intact face recognition, which suggests the mechanisms are not qualitatively different, only broken somewhere. The authors read the whole pattern as disconnected links between intact visual memory traces and later semantic processing, and draw the sharper implication that activating a stored face representation is not sufficient for conscious recognition. Note the size: twelve participants, with the covert signal in six.
wat. Shown a famous face they swore they had never seen, half of these participants produced the brain signature of knowing it anyway.
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It changes the diagnosis from a storage problem to a wiring problem. The faces are in there, and activating the stored representation turns out not to be enough on its own for conscious recognition.
How do we know?
Eimer, Gosling and Duchaine recorded electroencephalography while 12 people with developmental prosopagnosia judged the familiarity of famous and non-famous faces, and computed event-related potentials for each outcome separately.
What is still unknown
Twelve participants, with the covert signal appearing in six of them, so this establishes the phenomenon rather than its prevalence. Event-related components are interpreted by convention, not read off directly.
Learn something?
Where to next
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