You might have heard of prosopagnosia, a cognitive disorder that results in an inability to recognize familiar people by their face. It can be so severe that sufferers even have difficulty recognizing the face of friends, loved ones, or family members.

This condition actually has a lesser-known and under-researched cousin called phonagnosia, which results in the inability to recognize the voices of familiar people.

A new study reported in Brain and Language has estimated that more than 3 percent of people might be born with phonagnosia, most of whom don’t even realize they have it. Psychologists from the University of Southern California surveyed 730 participants. Out of those, 23 respondents were believed to have phonagnosia.

The web-based survey showed the participants four headshots of a notable person, such as a politician, musician, or actor. It was ensured the participant knew all of these people beforehand. They then listened to two short audio clips of a person talking: one was a non-celebrity and one was the voice of one of the pictured celebrities. The task was to say which audio clip was the celebrity voice and then identify which celebrity it was. They were also given an imagination test. This involved asking them how easily they could imagine the voices of certain celebrities, along with inanimate sounds such as breaking glass.

On average, people had a 76 percent accuracy in identifying the celebrity voice. However, 3.2 percent of the sample scored more than 2.28 standard deviations lower than this. The researchers concluded that these people are likely to suffer from a notable inability to recognize voices, with symptoms suggestive of phonagnosia.

The study authors noted that older people actually tended to perform better on the tests, suggesting that people are born with phonagnosia. This is different than prosopagnosia, which is often acquired later in the life through trauma or brain damage.

The study was on the small side, so it is difficult to apply these findings to the whole population. Nonetheless, the authors say this is likely to be the largest study ever conducted into the potential prevalence of phonagnosia. The British Psychology Society has said it hopes the study can raise awareness of this condition and foster further research.