Hearing and Understanding ONE Voice Among Many Sounds
How is it that you can hear and understand one particular person over another, even if they are both talking equally loud?
Researchers are just beginning to understand how a human does it... Before explaining, lets use an analogy.
In the past, I used the analogy of an old antenna based radio to explain how human hearing works... A given antenna radio has a volume knob that one can adjust up or down (as would occur with a hearing aid) as well as antenna reception which allows one to get a clear signal vs one full of static.
The ear is like the volume knob and the brain is the antenna... As such, if the reception is bad and there's a lot of background static, a person will have a hard time understanding what is being said on the radio... regardless of whether the volume knob is turned up all the way or not.
Similarly, if the brain is not filtering out the background noise to isolate the sound or person you want to hear and understand, you will have a hard time understanding what is being said.
While the ear indiscriminately hears everything, I've always just stated "the brain" acts to filter out the background noise you don't want to hear, but nobody really understood how, until recently...
Researchers in New York determined that there are different regions of the brain that perform this sound filtration that is completely separate from the auditory cortex (part of the brain that "hears" sounds transmitted from the ear).
Furthermore, the brain areas responding only to the selected voice constantly fine-tunes the reception to allow further improvement in comprehension over time... just like fiddling with an antenna to get as clear a signal on a radio station.
If the brain is not able to properly focus and filter the sound, the individual will have a hard time understanding conversation in a noisy environment, regardless of whether the person has normal hearing or not (for example, in patients with ADHD).
Of course, if hearing loss is also present along with an unfocused brain, it just makes it that much harder (for example, in the elderly who not only have hearing loss, but also decrease in brain function as well).
On the opposite extreme are people who make their living focusing on a specific sound among many sounds and have much greater ease in understanding people talking in a noisy environment. Take professional musicians in an orchestra who excel at hearing a single instrument during a Beethoven orchestral performance.
Hear That? In A Din Of Voices, Our Brains Can Tune Into One. NPR 3/6/13
Mechanisms Underlying Selective Neuronal Tracking of Attended Speech at a “Cocktail Party”. Neuron, Volume 77, Issue 5, 980-991, 6 March 2013