MadSci Network: Other

Re: When you bat your eyelashes, why don't you hear a sound?

Date: Tue Mar 10 09:39:51 1998
Posted By: Lori Holt, Graduate (Ph.D.) Student, Psychology, Ph.D., University of Wisconsin
Area of science: Other
ID: 888708452.Ot


There are probably a couple of reasons why we don't usually hear our 
eyelashes batting.

First, whatever sound our eyelids produce when we blink is very quiet. Our 
hearing system is extrmemely sensitive, but very quiet sounds are easily 
"masked" or "covered up" by other, louder, sounds in our environment. If 
you really pay attention I bet you will find that most rooms you are in 
actually have a good deal of noise even when they seem quiet. Listen 
carefully and you'll probably notice the rumble of a fan or a heater, noise 
from other parts of the building, maybe even voices from another room. 
Sounds like these can mask our ability to detect other very quiet sounds. 
If you were in a special sound-proof room that blocks all of these extra 
sounds, you might be able to hear your eyelids blink! However, even in a 
sound-proof room you might not hear your eyelashes batting because another 
process is at work.

Our brains work in such a way that messages from the outside world that are 
constant and relatively unchanging are not as "noticeable" as those that 
change quickly. Think of touch for example. Most of the time you are 
probably quite unaware of the touch of your clothes on your body. They are 
constantly touching you, but you don't really perceive them. This is a form 
of what is called adaptation. When a message from the world is pretty 
constant, our brains seem to begin to "ignore" them after time! Adaptation 
occurs in hearing too. We must constantly blink our eyelids, so any sound 
created by batting your eyelashes may be hard to hear due to adaptation.

If you have more questions, feel free to email me.
Lori Holt

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