Expert: Walter Hintz - 9/7/2006

Question
Dear expert,

I understood that the shape of pinna directs sounds into inner ear where we have multiple individual detectors each of them responsible for particular direction. Similar to the way eye is build with lens=pinna (directing) and retina=inner ear (multiple detectors).

Is that correct ?

If so, distorting the direction channel should change the perception. I did an experiment and plugged both ears with fingers. My 3D sound perception is unchanged. This is in contract with eye, where touching the eyelead clearly distorts vision.

could you provide me with further directions ?

thanks

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Followup To

Question -
Dear expert,
I'm interested in mechanism allowing human body to perceive direction of incoming sound. Since we have only 2 detectors (ears) on both side of the head this could explain left/right discrimination. However we have equally well developed front/back and up/down direction perception. For that to work we need at least 4 detectors. How this works ?

Answer -
Hi Andrew
It all has to do with those funny shaped ears that we have. The outer ears (pinna) do not detect nor percieve sounds they merely direct the sound waves into the inner ear If we only had two holes instead we would lose most of our directional sounds. Primate ears are designed  to capture sounds from all directions. Sometimes we may turn our heads slightly to gather in sounds and if you cup your ears you can increase the volume.
 Think how other animals like horses have to move ears to pick up sounds. We cannot do this and we do not need to. Lizards just have a hole and must turn the head in the direction of the sounds.

Answer
Sound waves are not distorted  by changing the direction from which they enter the ear.I am afraid I do not know what you mean be multiple detectors. Plugging the ears changes the amplitude but not the wave length  The vibrations that stimulate the auditory nerve are imterpreted by the brain.
Whether the light rays fall on the focal point of the retina depends upon the shape of the eyeball.  Pressure distorts it.
 Some of this is conjecture on my part but it kmakes sense to me,