The brain region responsible for one of humankind鈥檚 neatest mental tricks may have been identified.
We think nothing of singling out one person鈥檚 voice at a party buzzing with people chatting. But researchers have struggled to understand just how the human brain manages to filter out a single thread of conversation from a tangle of similar background noises.
The phenomenon was labelled the in the 1950s by , a British cognitive scientist.
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Now, if we don鈥檛 know exactly how, at least we may know where. Researchers conducting brain scans of people listening to multiple sounds, say that the secondary auditory cortex 鈥� located in the temporal lobe at the side of the head 鈥� does much of the work.
Hidden tone
at the Ruprecht-Karl University of Heidelberg in Germany and his team decided to study brain activity during this 鈥渋nformational masking鈥�.
They hooked volunteers up to a imager and played them a sound file containing a large number of randomly repeating tones across a range of frequencies (, mp3 format).
Hidden inside the track was one regularly repeating tone (, mp3 format), masked by random beeping (, mp3 format). Subjects were asked to ignore the random tones and press a button when they heard the regular tone.
Gutschalk鈥檚 team found that when subjects became aware of the regular tone, there was a surge of activity in the secondary audio cortex. 鈥淚n fact, we see the activity even before the subject presses the key, which is interesting,鈥� says Gutschalk.
Missing pitch
However, because the repeating sound was buried deeply in the sound file, some subjects failed to find it in the mix. When this happened there was no extra activity in these subjects鈥� secondary auditory cortex.
The results suggest that sound travels a long way 鈥� through the outer and inner ear, the thalamus and the primary auditory cortex 鈥� before the brain begins understand what it is hearing.
at the University of Sheffield, UK, points out that Gutshalk鈥檚 experiments did not include all the factors involved in the cocktail party effect. For example variations in pitch and timbre would also be involved in a real life situation.
Gutschalk agrees: 鈥淭his isn鈥檛 exactly the cocktail party phenomenon, but the mechanism we have identified probably plays an important role in the cocktail party effect,鈥� he says.
Journal reference:
The Human Brain 鈥� With one hundred billion nerve cells, the complexity is mind-boggling. Learn more in our cutting edge special report.
