American scientists have found out how “the cocktail party effect” works. The cocktail party effect is the well-known human ability to focus on the speech of one person in a large crowd and with a lot of background noise.
The cocktail party effect has both psychological and neurological components, the researchers found. All the sounds enter the ears as a cacophonous roar, but the brain processes the information and tunes into one sound, e.g. a person's voice, and filters out the rest.
“The psychological component is that it's a sound we want or need to hear which is why we can tune into it,” said co-author Dr. Edward Chang, assistant professor of neuroscience at the University of California, San Francisco, who made the discovery together with electrical engineer Nima Mesgarani.
Cocktail party effect in the auditory cortex
The researchers performed a series of trials on three volunteer patients with normal hearing who were undergoing brain surgery for severe epilepsy. 256 electrodes were placed directly over the cortex, the brainâ€™s outer surface.
To study the cocktail party effect, the patients listened to the recorded voices of two people, each speaking conflicting sentences simultaneously and the patients were asked to pick out one of the speakers and identify the words that were being said.
As the patients carried out their part of the experiment, succeeding 75% of the time, the electrodes recorded the location in the brain where the sentences they focused on we being processed.
â€œWe found that the entire auditory cortex of the brain was involved in processing the words,â€ Chang said. â€œIt has an extremely robust ability to handle conflicting sounds. It is a very smart organ.â€
â€œThe combination of high-resolution brain recordings and powerful decoding algorithms opens a window into the subjective experience of the mind that weâ€™ve never seen before.â€
Could predict speaker and words
The researchers applied decoding methods to reconstruct what the subjects heard from analysing their brain activity patterns. They found that the neural responses in the auditory cortex only reflected those of the targeted speaker. The decoding algorithm could predict which speaker and even what specific words the subject was listening to.
“The algorithm worked so well that we could predict not only the correct responses, but also even when they paid attention to the wrong word,” Chang said.
The findings about the cocktail party effect were published in the journal Nature.