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What is the prevalence of developmental prosopagnosia? An Empirical Evaluation of Different Diagnostic Cut Points
Summary
The prevalence of developmental prosopagnosia (DP), lifelong facial recognition deficits, is widely reported to be 2 to 2.5%. However, PD has been diagnosed in different ways in studies, resulting in different prevalence rates. In the current research, we estimated the range of PD prevalence by administering well-validated objective and subjective facial recognition measures to an unselected web sample of 3,116 individuals aged 18 to 55 years and applying PD diagnostic cutoffs from the last 13 years. We found that estimated prevalence rates ranged from 0.64 to 5.42% when using a z-score approach and from 0.13 to 2.95% when using a percentile approach, with the most commonly used cutoffs by researchers with a prevalence rate of 0.93% (z-score) (45% when percentiles are used). We next used multiple cluster analysis to examine whether there was a natural clustering of poorer facial recognizers , but failed to find consistent clustering beyond those with generally above or below average facial recognition. Finally, we investigated whether PD studies with more relaxed diagnostic cut-off points were associated with better performance on the Cambridge Face Perception Test. In a sample of 43 studies, there was a weak, non-significant association between increased diagnostic stringency and reduced PD facial perception accuracy (Kendall’s tau-b correlation, τb = 0.176 z-score; τb = 0.111 percentiles). Together, these results suggest that researchers have used more conservative PD diagnostic cutoffs than the widely reported prevalence of 2% to 2.5%. We discuss the strengths and weaknesses of using more inclusive cut-off points, such as identifying mild and major forms of PD according to the DSM-5.
Comments
Face blindness , a puzzling condition that can fool us into thinking we recognize people we have never met or cause us to not recognize those we know, has previously been estimated to affect between 2 and 2.5 percent of people in the world. Now, a new study by researchers at Harvard Medical School (HMS) and the Boston VA Healthcare System provides new insights into the disorder, suggesting it may be more common than currently believed.
Published in the journal Cortex , the study’s findings indicate that up to one in 33 people (3.08 percent) may meet the criteria for face blindness or prosopagnosia . This translates to more than 10 million Americans, the research team said.
The study found similar face-matching performance between people diagnosed with prosopagnosia using stricter versus more flexible criteria, suggesting that diagnostic criteria need to be expanded to be more inclusive. That could lead to new diagnoses among millions of people who may have the disorder but don’t realize it.
In the new study, led by Joseph DeGutis, HMS associate professor of psychiatry at VA Boston, researchers found that face blindness falls on a spectrum , one that can vary in severity and presentation, rather than representing a discrete group. The authors also provide diagnostic suggestions for identifying mild and major forms of prosopagnosia based on the guidelines for mild and major neurocognitive disorders of DSM5, the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders.
The study results are based on a web-based questionnaire and tests administered to 3,341 people. First, the researchers asked the participants if they experienced difficulties recognizing faces in their daily lives. They then administered two objective tests to determine whether they had difficulty learning new faces or recognizing very familiar famous faces.
The results showed that 31 individuals out of 3,341 had major prosopagnosia , while 72 out of 3,341 had a milder form . The researchers also noted that there were no clearly divided discrete groups of people with poor or good face recognition ability. Rather, the ability to recognize faces appeared to be on a continuum , they said.
Finally, the researchers compared face matching scores between people with prosopagnosia diagnosed using different criteria and found that using stricter diagnostic cut-offs did not correspond to lower face matching scores.
Harvard Medicine News spoke with DeGutis, the study’s lead author, about the implications of the findings .
Harvard Medicine News: Let’s start with the basics. What causes face blindness?
DeGutis: Prosopagnosia, or face blindness, can be caused by a brain injury in the occipital or temporal regions, known as acquired prosopagnosia , which affects one in 30,000 people in the United States. Prosopagnosia can also be a lifelong condition caused by genetic or developmental abnormalities , called developmental prosopagnosia , affecting one in 33 people.
HMNews: This is a fascinating condition, but some might say it is not a serious health disorder, so why is it important to study and understand?
DeGutis: First, face blindness can be a socially debilitating disorder that can limit employment opportunities. For example, networking is extremely difficult for people with prosopagnosia and can cause social distress and embarrassment. Recognizing someone is a social signal that indicates that “you are important to me.”
Prosopagnosia can also affect people on the autism spectrum and may also be a consequence of age-related cognitive decline . In a world where social isolation is on the rise, especially in teenagers and young adults, fostering and maintaining social ties and good face-to-face interactions are more important than ever.
HMNews: What sparked your interest in this field? What intrigues you most about how the brain sees and remembers faces and why?
DeGutis: Face blindness is fascinating on several levels. Humans are remarkably good at recognizing familiar faces and this is done with very little effort. We know that this facial "superpower" is based on several specific perceptual processes: holistic processing of the face: seeing the face as an integrated whole, for example; memory processes, easily associating faces with person-related knowledge; and also specialized mechanisms and brain regions, such as the fusiform area of the face.
Our knowledge of facial recognition in healthy people provides a very strong framework for understanding the ways in which these processes can fail in prosopagnosia. The processes also provide clues on how to improve facial recognition in people with face blindness, which is one of the main goals of our laboratory. Finally, studying prosopagnosia is fascinating from a phenomenological perspective: what do people with face blindness actually “see” when they look at a face? What comes to mind when you think of the face of a familiar friend?
HMNews: You say your findings require an expansion of diagnostic criteria. Why is that important?
DeGutis: This is important on several levels. First, most researchers have used overly strict diagnostic criteria , and many people with significant facial recognition problems in daily life have been mistakenly told that they do not have prosopagnosia. Expanding the diagnosis is important because knowing that you have real objective evidence of prosopagnosia, even a mild form, can help you take steps to reduce its negative impacts on daily life, such as telling your coworkers or seeking treatment.
Recent evidence suggests that people with milder forms of face blindness may benefit more from certain treatments than people with more severe forms of the condition. These treatments may include cognitive training to improve perceptual skills or training aimed directly at improving facial associations.
Finally, factors such as age-related cognitive decline and social anxiety can further worsen facial recognition skills. Knowing if you have mild prosopagnosia could help you keep an eye out for other situational or age-related declines in facial recognition ability.
HMNews: What do you want doctors and people with the condition to take away from these results?
DeGutis: The take-home message is that prosopagnosia is on a continuum , and the stricter versus more flexible diagnostic criteria used in prosopagnosia studies over the past 13 years have identified mechanically very similar populations, justifying expanding the criteria to include those with milder forms of it.
Another take-home message is the importance of using a combination of self-reported daily living difficulties and validated objective measures when diagnosing prosopagnosia. Relying only on self-reports has advantages and disadvantages because it can be challenging to judge your own abilities or rely solely on objective laboratory measures that may not reflect everyday life.
