Recognizing a familiar face whether it's greeting a colleague or spotting a friend in the crowd, plays an important role in social interactions. However, in people with lifelong difficulties in the processing of familiar faces, these effortless tasks can be quite challenging. These individuals suffer from a condition called developmental prosopagnosia in which they experience lifelong difficulty in recognizing faces despite having normal vision and no brain injury.
Since the condition often goes undiagnosed, accurate and accessible screening tools are essential for identifying the condition. Now, a study led by Associate Professor Masaki Mori from the Graduate School of Advanced Science and Technology, Japan Advanced Institute of Science and Technology (JAIST), Japan, along with former graduate student, Ms. Midori Sugiyama, from the Graduate School of Media and Governance, Keio University, Japan, provide the first comprehensive evaluation of the 20-item prosopagnosia index (PI20), a self-report questionnaire widely used to screen for developmental prosopagnosia. The PI20 asks people to rate how strongly they agree with 20 statements about everyday face-recognition experiences, such as recognizing familiar people out of context or remembering faces after meeting someone. The findings of the study were published in Volume 58 of the journal Behavior Research Methods on August 12, 2026.
To evaluate how well the questionnaire performs, the researchers used two complementary statistical approaches: classical test theory and item response theory. The first approach mainly examines whether the questionnaire consistently measures what it is intended to measure, while the second approach goes a step further by evaluating how well each question distinguishes between people with different levels of face-recognition difficulty.
Together, these analyses confirmed that the PI20 is an effective screening tool while identifying specific questions that could be refined to improve its accuracy.
"We evaluated the measurement characteristics of the PI20, one of the most widely used screening questionnaires for developmental prosopagnosia, to facilitate its appropriate use and development," says Dr. Mori.
The researchers analyzed responses from 599 Japanese adults for PI20 questionnaire. The analyses revealed that the PI20 has excellent reliability and validity, confirming its effectiveness as a screening tool. Several questions describing real-world situations were quite effective at distinguishing individuals with different levels of face-recognition difficulty.
Additionally, the study also identified opportunities for improvement. Two questions contributed relatively little to measuring face recognition. One question focused on recognizing people with distinctive facial features. Since unusual or highly distinctive faces are easier for most people to remember, the question may not effectively capture the specific face-recognition difficulties associated with developmental prosopagnosia. Another question was about recognizing one's own face in photographs, even though most people with developmental prosopagnosia may not experience much difficulty recognizing themselves. Overall, the findings suggest that while most items adequately capture the characteristics of developmental prosopagnosia, certain items may not be suitable for screening for developmental prosopagnosia.
Beyond evaluating the PI20, researchers have also made one of the largest PI20 datasets and the accompanying analysis code publicly available. This could prove valuable for future studies across different languages and cultures. By strengthening the scientific foundations of one of the field's widely used questionnaires, the study brings researchers one step closer to identifying the people with developmental prosopagnosia more accurately.
"Our study provides open materials and evidence to revise and further improve PI20 for the screening of developmental prosopagnosia," concludes Dr. Mori.
