In the savage world of nature, the ability to hear – and hear well – is a survival trait. Many animals rely on their keen sense of hearing to detect danger lurking in the savannah brush.
Some animals have hearing mechanisms like humans. Others hear with their entire bodies. And although many animals have very sophisticated acute hearing for survival reasons, a recent study demonstrated humans actually can distinguish between pitch better than other animals.
Auditory Neurons and Human Hearing
Sound signals are delivered to the brain in the form of electrical impulses. Nerve fibers carry these electrical signals to neurons in the human brain. (Stay with me.) In the brain, neurons process the sound – determine its source, its location and its threat level in a split second.
Researchers conducting studies at the Hebrew University’s (Jerusalem) Weizmann Institute for Science demonstrated that a single human neuron has more “discretion” in determining the frequency of a sound than other animals.
Visit an orchestral performance and you’ll immediately understand sound frequency. Instruments like the piccolo produce a high-frequency sound while an oboe produces a low-frequency sound. Not too hard, right?
Well, in a report in the professional journal, Nature, Dr. Itzhak Fried, a professor of neurosurgery and the Director of the Institute’s epilepsy surgery programs, describes his team’s research in humans and determined that a single auditory neuron (brain cell) “exhibits an amazing selectivity to a narrow sound frequency range, roughly down to one-tenth of an octave” – an octave being the "do-re-mi" we all learn as kids. In other words, that single brain cell is able to distinguish between high and low frequencies with more accuracy than the hearing neurons of other animals. (Take that, bears!)
“The results surprised the researchers. A single auditory neuron from humans showed an amazing sensitivity to distinguish between very subtle frequency differences, down to a tenth of an octave. This compared to a sensitivity of about one octave in the cat, about a third of an octave on average in rats, and half to one octave in the macaque.”
“This is remarkable selectivity,” said Fried, who is also the co-director of UCLA’s Seizure Disorder Center. “It is indeed a mystery why such resolution [hearing ability] in humans came to be. Why did we develop this? Such selectivity is not needed for speech comprehension, but it may have a role in musical skill. The three percent frequency differences that can be detected by single neurons may explain the fact that even musically untrained people can detect such frequency differences.
There is also evidence that frequency discrimination in humans correlates with various cognitive skills, including working memory and the capability to learn, but more research is needed to clarify this puzzle.”
The Amazing Auditory Neuron
|3-D Image of a Human Neuron|
The ability of a single auditory brain cell to multi-task also came as quite a surprise to researchers and hearing professionals. Patients were exposed to both artificial and real world sounds, including the sound track from the movie The Good, the Bad and The Ugly. Test subjects were also exposed to routine background noise. Researchers, tracking the activity of the brain cells tasked with interpreting sound “exhibited complex activity patterns, which could not be explained based solely on the frequency selectivity of the same neurons. This phenomenon has been shown in animal studies but never before in humans.”
So, each hearing brain cell can adapt instantly to pick up high or low frequencies, though researchers still don’t understand why humans would develop this remarkable skill. However, one researcher did point out that humans do create music that might be related to our ability to discern a variety of frequencies from all those hearing cells in out brains.
Indeed, the brain is a remarkable machine and today, we’re just beginning to learn its capabilities.
In regards to how well we hear other animals still have us beat on acuteness and range of hearing. For example, the deer has more acute hearing than humans meaning they can hear much softer sounds than the human auditory system can. This acute hearing protects them from dangers that may be feet or yards away.
However, humans have a greater ability to distinguish high and low frequencies from a single brain cell than other animals – and by a significant margin. But as with all good science, this research brings up more questions than it answers.
Why do humans have this ability? What purpose does it serve? It’s not needed for speech recognition according to studies so what, in our distant past, enabled us to hear a full range of frequencies with a single brain cell better than other animals.
And, since music has been a part of humanity for millennia, it’s fair to assume that this ability to distinguish frequencies has been a part of the human anatomy for a long, long time.
Further studies can now be undertaken to examine the range of hearing a single auditory neuron is capable of processing which, in turn, may lead to a better understanding of how the human brain functions in respects to hearing and pitch perception..