Scientists at the University of California-San Francisco (UCSF) have shed light on the workings of selective hearing - how people can tune in to a single speaker while tuning out their crowded, noisy environs (Nature, April 19, 2012).
Psychologists have known for decades about the so-called "cocktail party effect," a name that evokes the Mad Men era in which it was coined. It is the remarkable human ability to focus on a single speaker in virtually any environment - a classroom, sporting event or coffee bar - even if that person's voice is seemingly drowned out by a jabbering crowd.
To understand how selective hearing works in the brain, UCSF neurosurgeon Edward Chang, MD, of the Keck Center for Integrative Neuroscience, and postdoctoral fellow Nima Mesgarani, PhD, worked with three patients who were undergoing brain surgery for severe epilepsy. Part of this surgery involves pinpointing the parts of the brain responsible for disabling seizures. The epilepsy team finds those locales by mapping brain activity over a week by placing a thin sheet of up to 256 electrodes on the cortex. The electrodes record activity in the temporal lobe, which is home to the auditory cortex.
UCSF is one of few leading academic epilepsy centers where these advanced intracranial recordings are done. The ability to record safely from the brain itself provides unique opportunities to advance the fundamental knowledge of how the brain works.
"The combination of high-resolution brain recordings and powerful decoding algorithms opens a window into the subjective experience of the mind that we've never seen before," said Dr. Chang, who is also co-director of the Center for Neural Engineering and Prostheses at UC-Berkeley and UCSF.
During the experiments, patients listened to two speech samples played simultaneously in which different phrases were spoken by different speakers. They were asked to identify the words they heard spoken by one of the two speakers.