Wednesday, 20 April 2011

SD329: Book 2 - Hearing and Balance

Book 2, Block 3 is all about hearing and balance.

It starts off discussing what sound is, and how it is quantified. It looks at waveforms and analysis of sounds, and what filters do. So with the basics in place, the process of hearing can be discussed.

The next chapter discusses the structure of the ear. The three major components, outer, middle and inner. Also what are the vital parts of it, and what goes where. Several diagrams and more than a few Latin names for tissues.

Next we're on to how the sound is received and processed. How frequency is discriminated, how intensity is encoded. You have to remember that nerves only fire on or off, and so there are various schemes for encoding what you hear. Frequency or pitch can be encoded by phase locking to the signal and the nerve firing on every cycle. However this can only work for a small range, as the nerves themselves have a limited firing rate - therefore the position from cochlea to brain is preserved to allow placement to mark frequency. Similarly for intensity, although it all gets a bit complicated. Then there is the whole subject of processing - how do you know a sound is coming from the left or right, front/back, up down.

Finally as a wrap up to sound a chapter on the perception of sound.

All this is supplemented by another book full of essays about each topic that you are directed to read at the appropriate time, which go into far more depth on the subject.

The last chapter looks at the sense of balance, and how that works. Detection of being the right way up, and acceleration and how that is linked to other senses, such as turning your head towards a sound (very useful if you are potential dinner). It will come up again linked to vision where there is a special circuit to keep your eyes focused on something despite moving your head.

A very interesting book and topic.

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