New research has found that only two words are enough for people with normal hearing to distinguish the voice of a close friend or relative amongst other voices.
"The auditory capacities of humans are exceptional in terms of identifying familiar voices. At birth, babies can already recognize the voice of their mothers and distinguish the sounds of foreign languages," said researcher Julien Plante-Hebert from the University of Montreal in Canada.
The study involved playing recordings to Canadian French speakers, who were asked to recognize on multiple trials which of the ten male voices they heard was familiar to them.
To evaluate their auditory capacities, Plante-Hebert created a series of voice "lineups," a technique inspired by the well known visual identification procedure used by police, in which a group of individuals sharing similar physical traits are placed before a witness.
"A voice lineup is an analogous procedure in which several voices with similar acoustic aspects are presented. In my study, each voice lineup contained different lengths of utterances varying from one to eighteen syllables," Plante-Hebert pointed out.
Forty four people aged 18-65 years participated in the experiment. Plante-Hebert found that the participants were unable to identify short utterances regardless of their familiarity with the person speaking.
However, with utterances of four or more syllables the success rate was nearly total for very familiar voices. "Identification rates exceed those currently obtained with automatic systems," he said.
"While advanced technologies are able to capture a large amount of speech information, only humans so far are able to recognize familiar voices with almost total accuracy," he concluded. The study will be presented at the 18th International Congress of Phonetic Sciences in Glasgow, Scotland.