Given my inability to recognize faces, I've developed a number of compensatory mechanisms. One is that I remember people by memorizing specific features; he's the guy with curly black hair, she's the woman with small oval glasses and a tattoo on her right hand. I notice how people walk and how they carry their posture; I can sometimes recognize people I know well even if they're walking away from me, if they have a distinctive gait (which many people do, whether they realize it or not).
But for me the most important thing is the sound of their voices. I think that may be why it took me so long to figure out I'm face blind; often, all people have to do is say a few words and I immediately know who they are, so the fact that their faces don't trigger the immediate recognition most people have doesn't hamper me as much.
It turns out that I'm not alone in relying on vocalizations for identifying who's around. According to a paper last week in Science Advances, zebra finches have an ability to recognize their flock mates' unique vocalizations that rivals that of most humans.
In "High-Capacity Auditory Memory for Vocal Communication in a Social Songbird," a team composed of biologists Kevin Yu, William Wood, and Frederic Theunissen, all of the University of California-Berkeley, used rewards to train a bunch of Australian zebra finches (Taeniopygia guttata) and see how far they could push the birds' ability to distinguish between the vocalizations of different members of their species. And surprisingly -- at least to anyone who has heard the twittering cacophony of a cageful of zebra finches -- these birds could distinguish between the voices of forty or more of their friends.
The authors write:
This is the first time this kind of individual vocal recognition has been demonstrated in a non-human animal. "For animals, the ability to recognize the source and meaning of a cohort member's call requires complex mapping skills, and this is something zebra finches have clearly mastered," study co-author Theunissen said, in an interview with Science Direct. "They have what we call a 'fusion fission' society, where they split up and then come back together. They don't want to separate from the flock, and so, if one of them gets lost, they might call out 'Hey, Ted, we're right here.' Or, if one of them is sitting in a nest while the other is foraging, one might call out to ask if it's safe to return to the nest... I am really impressed by the spectacular memory abilities that zebra finches possess in order to interpret communication calls. Previous research shows that songbirds are capable of using simple syntax to generate complex meanings and that, in many bird species, a song is learned by imitation. It is now clear that the songbird brain is wired for vocal communication."
Effective vocal communication often requires the listener to recognize the identity of a vocalizer, and this recognition is dependent on the listener’s ability to form auditory memories. We tested the memory capacity of a social songbird, the zebra finch, for vocalizer identities using conditioning experiments and found that male and female zebra finches can remember a large number of vocalizers (mean, 42) based solely on the individual signatures found in their songs and distance calls. These memories were formed within a few trials, were generalized to previously unheard renditions, and were maintained for up to a month. A fast and high-capacity auditory memory for vocalizer identity has not been demonstrated previously in any nonhuman animals and is an important component of vocal communication in social species.