AN, a 23-year-old private tutor in Georgia, had never really thought about how one might identify different voices. Most people effortlessly recognize who is on the other side of a telephone line and can quickly tell if they hear their favorite singers on the radio. But AN can't. And she wasn't ever aware of this, until one day a few years ago her boyfriend played her a new album by one of her favorite bands, and she just could not recognize who was singing.
"You can't tell who it is?' Like, you can't tell who it is from the voice?" her boyfriend had asked her.
"And then I realized a little bit that, no, I had no idea who the voice was," AN recalled, in an interview with Braindecoder.
Back then AN did not know that having trouble recognizing familiar voices was classified as an actual disorder. Later, in a class she was taking at the University of Southern California she heard about a condition: phonagnosia—a term derived from phone, Ancient Greek word for "voice," and agnosia, a loss of knowledge. That's when she thought she could indeed be phonagnosic. (AN's real name is not revealed in this story to protect her privacy.)
She eventually approached Irving Biederman, her instructor in her cognitive neuroscience course at USC and told him about her issues with identifying people by their voices. Biederman and his colleagues decided to study AN and two other phonagnosics they had enlisted.
Is this Jon Hamm speaking or Neil Patrick Harris?
People with phonagnosia are unable to recognize or imagine familiar voices, Biederman told Braindecoder. Phonagnosia also has its visual equivalent called prosopagnosia, or face blindness, a disorder in which a person is unable to recognize or imagine the faces of familiar people.
Interestingly, prosopagnosia and phonagnosia are specific to faces and voices, respectively, Biederman explained. People with prosopagnosia have no trouble dealing with non-face objects, and those with phonagnosia have no trouble recognizing or imagining non-voice sounds like rushing water or dog barking, he said.
AN has no history of neurological injury, and so her phonagnosia is thought to be developmental. But there have also been reports of an acquired form of the condition, typically as a result of damage to the right parietal region of the brain, the researchers said.
In the study, published recently in the journal Brain and Language, Biederman and his colleagues performed a series of experiments, hoping to better understand the mysterious disorder. In one of their experiments, they tested the ability to recognize the voices of celebrities in AN and 21 control participants. The list of celebrities in the study had been generated by AN herself, and included mainstream entertainers, politicians and news figures she had heard speaking. It turned out that AN did much worse at the voice recognition task than the controls.
Image: in one of the experiments, researchers played audio clips for AN and asked her to identify which celebrity the voice belongs to. Credit: Xu et. al., Brain and Language, 2015
It's not like all voices sound the same to AN. When the researchers tested her ability to differentiate between two unfamiliar voices, she was able to do so without any issues. "So she does not have a perceptual deficit in discriminating voices and telling one voice from the other," Biederman said.
In another experiment, one that tested AN's ability to imagine non-voice sounds like rushing water and the voices of celebrities, she was able to imagine the former but not the latter.
The researchers also examined brain activity (using fMRI brain scans) in AN and control participants during the celebrity voice imagination test and the non-voice sound test. They found that the controls exhibited greater activity in the ventromedial prefrontal cortex while they were imagining celebrity voices, than while they were imagining non-voice sounds. Conversely, AN did not show greater activation in this region of the brain when she was asked to imagine celebrity voices.
Interestingly, previous research has shown that the same brain region gets activated more when a person is shown familiar faces of famous people, compared with faces learned only recently through during an experiment.
Considering that AN does not seem to have perceptual issues with telling one voice from the other, what drives her disorder? The main issue, it seems, is her inability to associate the sound of a voice to her knowledge about a person, Biederman said. The researchers suspect that a communication line that carries information about familiar voices between certain regions of the brain may be missing, leading to AN's deficit.
Just like face blindness, phonagnosia may lead to tricky situations when social interactions are involved. Another phonagnosic mentioned in the study, a 66-year-old woman in England, said that for much of her life, she was reluctant to answer the phone because she did not recognize the voices of people who were calling, Biederman said.
In the age of caller ID, phonagnosia does not cause significant issues for AN, with certain minor exceptions. "I have gotten calls in the past like where my family put me on speaker, and all of a sudden I am talking to all these people, and I have no idea who I am talking to even if they are like my aunt, my grandmother," she said. "That can get a little awkward sometimes."