We get to know a lot of different faces in our complex, densely populated world. The first ballpark estimate by researchers indicates just how many — around 5,000.
To reach this estimate, Rob Jenkins at the University of York, UK, and his colleagues asked 25 participants to recall as many specific faces — of both famous people and people that the participants knew personally — as they could in an hour. To facilitate recall, the researchers gave participants spreadsheets listing categories such as ‘friends from school’ and ‘film industry’, and paid them a small sum for each recalled face of a famous person. On average, participants recalled around 550 faces.
Participants then reviewed images of 3,441 faces of famous people, this time without time pressure or financial incentive. On average, they recognized nearly 800 faces.
For each individual, the researchers calculated the ratio of number of famous faces recalled to number of famous faces recognized. That ratio was used to extrapolate from an individual’s recall number to the total number of faces each participant knew. That total averaged around 5,000 but varied considerably, ranging from 1,000 to 10,000.