Prosopagnosia, or face blindness, leaves eyesight, intelligence, and memory intact but strips away the ability to know who a face belongs to. John Hughlings Jackson noted cases in the 19th century, and in 1947 German neurologist Joachim Bodamer named it after treating a 24 year old with a bullet wound to the head who could recognize family only by voice, gait, or touch. This episode explains the right fusiform gyrus as the brain’s fast lane for faces and the difference between acquired cases, caused by trauma, posterior cerebral artery strokes, encephalitis, carbon monoxide poisoning, or degenerative disease, and the apperceptive and associative forms.

Most of the 2 to 2.5 percent of people with face blindness have the developmental form, and a 2005 study led by Ingo Kennerknecht pointed to autosomal dominant inheritance. Children may show no fear of strangers and prefer cartoons, whose characters always look the same, while adults identify people by hair, voice, jewelry, and gait. Testing moved from celebrity photos to the Benton Facial Recognition Test, which patients could pass by matching single features, and on to the Cambridge Face Memory Test and the PI-20. The inversion effect shows that normal face reading is holistic.

• Diamond and Carey’s study of dog show judges who struggled to recognize upside down dogs
• Brad Pitt, Jane Goodall, and Steve Wozniak as people who have described face blindness
• Oliver Sacks, who did not fully grasp the extent of his own face blindness for much of his life
• Research suggesting one third to one half of autistic people also have prosopagnosia
• A possible role for oxytocin receptor genes in that overlap