Nerve cells in the brains of songbirds are sensitive to specific sounds, and only respond when those sounds occur during communication, a recent study shows. The finding helps explain people's ability to listen to a conversation while in a noisy environment -- the "cocktail party effect."

The research was presented at Neuroscience 2010, the annual meeting of the Society for Neuroscience, held in San Diego.

"While the cocktail party effect has been well-documented, it is not clear exactly how our brains are able to separate different voices so well," said senior author Frederic Theunissen, PhD, of University of California, Berkeley. "In fact, background noise is a constant challenge for engineers who design hearing aids and voice-recognition systems. Knowledge about how our ears and brains solve this task could lead to substantial improvements in hearing aid performance."

To explore how people filter out different sounds, the researchers focused on the hearing processes of songbirds. The ways that humans learn to speak and birds learn to sing is strikingly similar, and there are also similarities in their brains' auditory structures.

The authors played sound recordings for zebra finches and noted the responses of individual auditory nerve cells. The neurons were exposed to bird songs, non-communicative noises, and combination of the two. Results showed that certain cells responded almost identically to a song note played in quiet and to the same note played over the noise. The study helps identify how these neurons extracted sounds in a challenging environment. "Our group has demonstrated that individual nerve cells can be very good at picking vocalization out of background noise," Theunissen said.

Research was supported by the National Institute on Deafness and Other Communication Disorders.