Jonathan Simon, an associate professor at the University of Maryland, Ph.D. graduate Nai Ding of the University of Maryland, lead author Elana M. Zion Golumbic of Columbia University and colleagues said in a crowded place, sounds from different talkers enter the ears mixed together.
It is the brain that must separate them using cues from where the sounds are coming. But people also have the ability to track a particular voice, which comes to dominate a person's attention and later, as memory, the researchers say.
The researchers used the brain-signal recording device electrocorticography implanted directly in the cortex of the brain used in epilepsy surgery. It consists of about 120 electrodes arranged in an array over the brain's lateral cortex.
With the permission of the surgery patients, researchers gave them a cocktail party-like comprehension task in which they watched a brief, 9-12 second movie of two simultaneous talkers, side by side. A cue in the movie indicated to which talker the person should try to listen.
The electrocorticography recorded what was happening in the patients' brains as they focused on what one of the talkers was saying.
The study, published in the journal Neuron, found the low-frequency "phase entrainment" signals and high-frequency "power modulations" worked together in the brain to dynamically track the chosen talker.