Saturday, November 03, 2012


About my Hearing

           On November 2, 2011, at about 6:55 AM I was involved in a serious auto accident.  My car and another vehicle collided almost head-on.  The air-bag in my vehicle deployed.  The windows of my vehicle were closed.  The result was a terrific acoustic shock to my ears.  At the same time my body lunged forward on to the steering wheel and  I suffered a broken sternum.  I was hospitalized until Saturday, November 5.  I came home and recuperated from the accident with the help of a hired care-giver during the day.  The pain in my chest, especially when I tried to lift myself from a lying position in bed was severe enough that I had to sleep in a Laz-e-boy reclining chair for more than a week.

            About a week after the accident I endeavored to play a recorder or longitudinal flute.  I was able to play correctly the notes from F (349 Hz) to B-flat (932 Hz).  The next note, C (1047 Hz) sounded like D-sharp (1245 Hz), a minor third higher in pitch.  Notes above that were similarly displaced upward in pitch by a minor third.  My first reaction was that I had forgotten how to finger the instrument correctly.  I went to the piano and played notes of the same range of pitch as those I had just played on the recorder.  The effect was the same.  Above 950 Hz all musical notes seemed to me to be a minor third too sharp or high in pitch.

            This was not hearing loss but pitch distortion.  It has persisted to this day (October 31, 2012).  It is no longer possible for me to enjoy music with notes that cross this strange discontinuity in my pitch perception.  I hear some favorite music by Bach, such as “Sheep may safely graze” or “Jesu joy of man’s desiring” and the high notes on a flute or recorder don’t sound right to me.  I am confined to enjoying music without the high notes above high B-flat.

            I have given this problem a lot of thought.  I haven’t found any account of another person who suffered this type of hearing change.  I have read that an air bag deployment can cause temporary deafness.  I haven’t found any literature on pitch perception change.  To be honest, I haven’t conducted a thorough literature search of the subject.

            I have worked out a model to explain what happened to my sense of hearing.  I start by imagining the little cilia in the cochlea, the little coiled tube in the inner ear.  Imagine the cochlea straightened out as illustrated in the left hand part of the following diagram.  On the left are the cilia or little bristles immersed in the fluid.  Any musical note that is transmitted to the inner ear causes the little bristles whose resonant frequencies are near the frequency of the note to vibrate. 

            One might think of a frequency meter for an electric generator with vanes or stiff metal reeds that vibrate. When the generator is running at the correct speed, the vane corresponding to 60 Hz vibrates with a large amplitude.  Vanes for adjacent frequencies, 60.1, 60.2, ..., 59.9, 59.8, etc, vibrate at amplitudes that are lower the farther the resonant frequency of the vane is from 60 Hz.  In the same way a single frequency excites several of the little bristles in the cochlea.

            Next, I come to the question of how does the nerve bundle convey this information to the brain?  Is each bristle part of a nerve that communicates its frequency directly?  That sounds highly unlikely.  One would have to have nerves that in a normal youthful human could conduct electrical impulses at a rate of up to 15,000 Hz and above.  Nerves don’t work that way.  In my model, each bristle is part of a nerve that transmits a regular signal in the range of 10 to 100 Hz whenever the bristle is caused to vibrate.  The frequency of the signal indicates the amplitude of the vibration.  In the brain, each nerve fiber is connected to an individual nerve cell.  That nerve cell interprets the incoming signal as a musical note.

            In the diagram above, G denotes the frequency at which the pitch displacement occurs.  The other notes in the diagram are self-explanatory.  The brain cells on the right enclosed in the heavy dashed line are those that the connections from the bristle nerve were originally attached to.  As a result of the concussion those connections were all shifted to nerve cells that interpret impulses as higher frequencies.

            There is one feature of my present hearing that the model doesn’t explain.  It is true that there is a gap or difference between my pitch perception below and above a frequency of about 950 Hz, at least in my right ear.  However, the pitch does not jump immediately by about a minor third (approximately 20 percent in frequency).  The perceived pitch changes rapidly but, as far as I can tell, smoothly from b-flat through b-natural to c.  The model can not be an accurate diagram of the mechanism of pitch perception in my head.

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