Tuesday, February 8, 2011

Here's your chance to play God...

Imagine it is your job to create a system to allow humans to detect sound. You are the person in charge of developing the auditory system (aka hearing!). Go!


Yup pretty much. Sounds difficult eh? Well good thing for you I'm here to help.

You would probably want to develop cells in the ear that detect sound- good place to start right?

You would have some cells detect different sounds too, right? What we call 'sounds' are simply differences in frequency- known by the lay person as 'pitch'. High pitch sounds are high frequencies and low pitch sounds are low frequencies. So, you would probably want different cells that are able to detect different frequencies.

Let's say you developed the auditory cells to hear frequencies from 200-800 hertz (hz)- which is actually the true case in humans- we hear sounds from about 200 to about 800 hz. Don't waste time developing one cell for 200 hz and another 201 hz- there is an immeasurable difference between the two! It would be a good idea to have some for 200 and some for 300, and for 400, etc. This way, when the one for 300 is fully activated, and the one for 200 is activated just a little bit, you know that you have 290 hz...and the same thing for the 300 and 400 cells if you had 310. Follow? In fact this is a simple version of how the human auditory system works...but here's where it gets tricky.

So, you have all of your cells that can detect specific frequencies of sound and, depending on how many are activated, etc, you can hear many different sounds. All is good in the world of hearing. Now we have to get this sound detection to the brain. Let's say we played a sound a sound at 300 hz over, and over, and over again. What would you want the brain to recieve as a message? I'm assuming you want the brain to recieve the exact same message every time a 300 hz sound is played, right? Makes sense...but apparently God (perhaps using his developmental tool of evolution) doesn't think this way. No- He decided that our auditory cells should send different messages to the brain each time it hears the same sound. This is explained in more detail below, but the cells respond either strongly or weakly, almost at random.

There is an average neuronal depolarization of about 33 millivolts each time a 300 hz sound is detected by the mammilian brain. This is an average...it could be 30, or 28, perhaps 51 or as high as 60. They will average to 33...but no one knows why it isn't 33 all the time.

Any thoughts as to why this would be? There are no known temporal or spatial mathematical relationships...try to think outside the box on this one.



  1. Because - when Ozzy hits that 300mhz, and Celine hits it, the brain interprets it a little different. How, I guess, is your preference....

  2. Ok, here's a thought. As a mother I've learned to be "in tune" with the sounds of my kids and my home. A mother learns to listen for the sounds of her baby's cry or movement to know what the baby needs are. As the family grows, the sounds change, she is listening for a new baby's cry as well as her son's sounds playing outside as well as listening for the washer to stop so she can put in another load of laundry. When the baby starts to cry at the same level she always uses when she first wakes up, the son starts yelling from outside because he was just bit by the dog (because he wouldn't stop teasing it!)the mother's brain still hears the baby's cry but not at the same level because now her focus is on the sound outside where she has to break up the son/dog situation. As she comes back in the house she again hears the baby's cry, now resumed to regular level. She goes and gets the baby from her crib and as she's walking back into the kitchen to start supper she now hears the washer slowing down. The sounds are all the same level but depending on priority, a mother is able to tune in and tune out the level she hears each sound depending on the importance of each sound at the time.

  3. Maybe it is a matter of priority.
    In Dad's case, maybe he prioritizes Ozzy over Celine...
    You have a good point that humans are not able to tune everything out and just 'hear' one sound- the collection of sounds that we are hearing (or that we are no longer hearing) has a huge impact on how we hear!

  4. In Psychology we learned that if we hear something over and over again, the brain recognizes this sound and then slowly drounds it out if it is not needed (background sound). This is how some people can read in loud areas, the constant sound of people talking, walking, or traffic becomes ammune to the brain and so the brain starts paying attention to what you are reading. This is why I like to listen to music when ever I am reading. I tend to list to other peoples conversations, get annoyed by papers moving or someone walking by (new sounds), but if I listen to the same song over and over again my brain will get used to this and it gets easier for me to dround it out. So then I just pay attention to what I am reading, and I retain a lot more by doing thing. Unless I am listening to a really good song, then I just start singing :P

  5. I remember in animal phys they talked about how we stop interpreting the hair cells firing after a bit, and then we only detect if there is a CHANGE in the firing frequency... Desensitization kind of like how you don't feel your clothes all day, but you do as soon as something makes you aware of them again. In Sass's case, she wouldn't notice the traffic unless someone started honking or the music unless her favourite song came on. And a mother could tune out her baby crying while she was preoccupied with her older son, but would tune right in again if the cry changed from the usual waking up cry... Perhaps?

  6. It seems as if everyone has some good idea! From Ozzy to babies, and traffic to clothes...sounds like a good explanation for me guys! Now if only we could do this with a couple of cells in a lab...or with people? :)