Normally, if you hear a sound, you have some idea of where the sound came from. But when a scuba diver hears a sound underwater, it is virtually impossible to tell where it came from.

1. Why?

2. Can you suggest some form of underwater hearing aid type device that would allow more accurate underwater sound localization?

(In reply to re(3): Questioning the answers... by ajosin)

Finally, the reason the ear is so much better at detecting time differences than the eye is because the ear is purely MECHANICAL (the ear drums move with the preassure wave). The eyes, on the other hand, use quemical processes which require some time to ocurr.

I have a new respect for our sense of hearing; What is the fastest moving part of your boddy?. The ear drum!.

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This is not quite true. First, both eyes and ears need to convert the signal to a neural impulse. Once it's been converted, everything is very quick, but that initial conversion is slow for both.

Second, even if light-to-neural spike conversion is slower, it is a constant delay. So two things happening 1/1000 of a second apart in two different locations of the eye will produce two neural spikes 1/1000 of a second apart (not so if it's in the same region, as neurons have a limit to how fast they can repeatedly spike, but this is true for the ear as well).

Our eyes use this time descrimination to good effect. Most movement information comes from movement-detector cells, which are activated when two neighboring retina cells fire one after the other in quick succession.

As for which is the fastest moving body part, the eardrum may be if you count being moved by an external source "fastest moving." The faster organ to be moved by muscle? The eye, which moves at up to 1000 degrees per second during a saccade.

:)

Posted by Sam on 2005-04-14 15:53:08