Ears to Bats

Ears to Bats

   An earlier post talked about the complexity of our ears and how important they are to our balance among other things;  and as mentioned then, the human hearing ability of sound is actually quite limited.  Still, our ears play an important part in letting us know where we are.  Suffer a concussion or have a bit too much to drink, and you'll feel the system start to break down.  The recent issue of Discover talked of one's man's recovery from being rear-ended and who happened to suffer vestibular system damage.  In his words: ...my already-overtaxed and poorly functioning visual system had to take on the extra load of providing for many of my balance needs.  But at the same time, any sort of high-level thinking also required those same visual/spatial systems to create the internal images of thought -- my damaged brain would rapidly grow fatigued...during even short periods of cognitive load, my balance would grow progressively worse and nausea would almost immediately set in.

   To briefly describe his condition, the author writes:  Roughly speaking, the balance system uses three overlapping components: the vestibular, or "inner ear," system, the visual system and proprioception, the feeling of our bodies in the space around us -- a position-movement sensation.  While the vestibular system is primary, the other two are also important...our vestibular and proprioceptive systems give direct information to our bodies to help them stay upright...the vestibulo-ocular reflex, for example, uses input from the brain's assessments of position and velocity to stabilize our gaze while we're moving.  You can see this effect by looking directly at your own eyes in a mirror and moving your body around.  In addition, these subsecond microadjustments are integrated with our ability to simultaneously adjust for the pursuit of objects moving in our environment as well, so we can turn our heads and bodies while still following the path of a bird flying across our yard.

   So where the heck do the bats fit in?  As it turns out, and as you likely already know, bats use echo-location, the bouncing of sound waves to pinpoint objects in front of them (other animals such as dolphins and now even some people who are blind use similar methods of detecting their location).  What was interesting was the use of different frequencies, specifically 61 kHz, 90.5 kHz and 122 kHz, each followed by a chirp.  The bounce-back (Doppler) pulse frequency the bats use adjusts for changes and is so sensitive that they can "process acoustic features like the wing beats of insects and even detect textures," according to a piece in Scientific American Mind (some moths have now developed a "jamming" frequency to partially confuse the bats).  The echo-location is part of the reason bats can emerge by the millions from a cave and not bump into one another (a spectacular video showing this in slow motion was captured on Science Friday on NPR).

   But what we hear and what bats hear is a far cry from what we are discovering about sound waves themselves.  The 20 Hz to 20,000 Hz range we humans have is little compared to what Discover titled the Sounds of Science by writer Mary Hoff (the full article will be available next month as the magazine doesn't post the current month's issue)...a Hertz or Hz is equal to one sound wave, those squiggly lines you would see on an oscilloscope.  At 0.00005-0.0009 Hz, the music of the stars emerge, gases creating "ultralow-frequency sound waves, appearing as rhythmic changes in brightness and temperature."  She goes on to show sound frequencies that plants, glaciers, fish, even forests are emitting and scientists are capturing, all in an effort to understand how large a role sound plays in our lives.

   Now scientists are discovering that our sound patterns, even something as simple as babies gurgling, can be analyzed and possibly used to detect the early stages of autism;  other sound frequency tests "could help doctors screen for several other cognitive and mental health ailments, such as dementia and depression, that can be difficult to detect in their early stages," according to the recent piece in Discover titled Altered Voices by author Sujata Gupta (this from their June issue so there's currently no link, but you can follow the author on Twitter, @sujatagupta).  The new test developed by Gordon Ramsay (not the chef but rather the director of the Spoken Communication Laboratory at the Marcus Autism Center in Atlanta, GA.) and researcher Ami Klin (also at the center) uses vocal recording analysis and costs $10 (vs. the $5,000 typically charged for an assessment); their earlier studies on an older age group of children showed an 86% accuracy rate.   Neuroscientists in Norway, Greece and France are running similar test studies with voice analysis for adults to test for changes in what might be a precursor to a diminished mental state such as "depression, bipolar disorder and schizophrenia"...one vocal test from Israel is completed in just five minutes.

   It would seem that despite our fine instruments and discoveries, we still have much to learn, even if it's right in front of us.  A simple sound might not prove to be so simple after all.  Perhaps our enjoyment of a symphony or a rock concert or a dinner conversation holds far more than we realized, our eyes and brains working full time to create an image of where we are and how we fit in, not only in our awareness and consciousness, but in the universe around us...now we find that the stars are talking, as are the forest and the oceans.  We may not think we can hear them with our ears...but maybe if we listen, really listen, our brains and eyes and ears can hear them after all.