The high-profile trial of George Zimmerman, a Florida neighborhood watch volunteer accused of second-degree murder in the shooting death of teenager Trayvon Martin in February 2012, last week featured what be one of the most unsettling moments ever seen in a criminal case. First, Martin’s mother, Sybrina Fulton, identified a voice crying out in a three-second segment of a 911 call as definitely that of her son Trayvon. Shortly afterward, she was followed on the stand by Gladys Zimmerman, who insisted, with just as much seeming conviction, that the voice was that of her son George, who has claimed that he was attacked by Martin.
While both women appeared sincere in identifying the voice as that of their sons, they can’t both be right. That leads us to wonder: How adept are we humans at recognizing the voices of our offspring? And what might cause a parent to mistake another voice for his or her own progeny?
It might seem like a no-brainer that parents would be able to pick out the voices of their own flesh-and-blood. After all, studies show that a wide range of animal species, from penguins to rhesus monkeys, possess the ability to aurally identify their offspring.
An Australian study published in PLOS ONE in 2012, for example, found that sea lions begin to recognize the distinctive cries of their pups within 48 hours of birth, and at 72 hours will turn to respond to their own pups’ vocalizations more quickly than they will to the cries of other pups.
British researchers reported in a 2012 article in Proceedings of the Royal Society B that pygmy goat mothers not only recognized the calls of their kids at five weeks, but were able to recognize recordings of them a year to 18 months after weaning. The scientists say that parental ability to recognize voices for such an extended time is useful, because, among other benefits, it helps keep mother goats from mating with their sexually mature sons.
You’d think that we would be pretty good at it, too. While humans may not be able to hear as wide a range of frequencies as some of these animals, we actually are more adept at detecting fine differences between frequencies, according to work by U.S. and Israeli researchers.
And like other primates, humans have complicated anatomical structures for making sounds, with plenty of individual variations -- such as the length and flexibility of the vocal tract -- that can make one person’s voice sound different from another, according to a 2006 article by University of Glasgow psychology professor Pascal Benin.
We also have big brains that devote a lot of their processing power to speech. A 2001 study by Japanese researchers, published in the journal Neuropsychologia, found that familiar voices activate different areas of our brains -- in particular, the right frontal pole and right temporal pole -- than the sound of people we don’t know.