Faces provide information about one’s gender, age, ethnicity, emotional state, and perhaps most importantly, they identify the owner. Thus, the ability to recognize an individual just by looking at their face is crucial for human social interaction. Prosopagnosia is a cognitive condition characterized by a relatively selective impairment in face recognition. The disorder can be acquired or developmental in nature, with the latter also referred to as “congenital” or “hereditary” prosopagnosia. The condition occurs in the absence of any neurological damage, socio-emotional dysfunction or lower-level visual deficits4, and may affect 2–2.5% of the adult population7 and 1.2–4% of those in middle childhood.
In the last 20 years, individuals with DP have been used to make theoretical inferences about the development and functioning of the cognitive and neural architecture of the typical and impaired face recognition system. Given some individuals also report moderate-to-severe psychosocial consequences of the condition , there has been increasing interest in the accurate diagnosis of DP via objective testing. Many researchers diagnose the condition using a combination of the Cambridge Face Memory Test (CFMT17) and the Cambridge Face Perception Test (CFPT18) - regarded as the leading objective tests of face recognition - and a famous faces test. Participants are thought to meet the diagnostic criteria for DP when their scores are considered together, and in many cases, this will mean that DP is determined when individuals score atypically on at least two of these three measures.
Unlike those with acquired prosopagnosia, those with DP have no point of comparison nor experience an abrupt loss of their face recognition skills: many individuals tested in our laboratory did not become aware of their difficulties until mid or even late adulthood (see also33,34). This is likely to be due to a combination of reasons. For instance, many people with prosopagnosia can identify people via voice, gait and general appearance and manner15. Face recognition difficulties have also been reported to be highly heritable (e.g. refs39,40) and individuals may be comparing their abilities to family members who are equally poor at recognizing faces. Subsequently, these individuals may not become aware of their difficulties for a long period of time. Additionally, some people with DP devise their own strategies to recognize others and cope relatively well with their difficulties33. This may conceal the condition from other people, or even falsely indicate to oneself, that they are able to recognize others in the same manner as most others in the general population.
If an unaffected person is to recognize the traits of DP in others (as would typically be required to identify the condition in children), they must first know that the condition exists and have an understanding of its behavioral manifestation on an everyday level.