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11 Cards in this Set
- Front
- Back
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Sound
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pressure variations propogated through air (think ripples). The is made possible because air is compressible.
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Sound waves
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sine wave variations
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Amplitude
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loudness (the amount of pressure exerted by each air particle on the next). The max height of the sound wave determines amplitude. It is measured in decibels (log, doubles with every 10 decibels)
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Frequency
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pitch. The timing of the crests (how much time elapses between the next one) is known as wavelength. The number of cycles per second (inversely proportion to wavelength) is frequency, which is measured in hertz.
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Fourier’s theorem
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sound waves can be broken down into frequency, amplitude, and phase.
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Audiogram
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a measure of how sensitive a person is to sounds of different frequencies/pitches. (Dogs can hear higher than humans can.)
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Ear diagram
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External ear –eardrum- ‡ middle ear –ossicles: malleus, incus, stapes. Footplate- ‡ inner ear –fluid-filled cochlea- ‡ auditory nerve ‡ thalamus ‡temporal lobe
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Why do we need external/middle ear?
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The external and middle ear serve as an interface between the soft, cushy air and the fluids of the inner ear. Since fluid is harder to move than air, sound must be amplified (which is why the eardrum is 20X the size of the middle ear). Note: bones can disarticulate to protect themselves from loud noises.
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basis of transduction
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in the cochlea. The footplate moves in synchrony with sound waves. The cochlea has a bony shell, a fluid- filled center, a stiff tectorial membrance, still hair cells, and a flexible basilar membrane. Pressure moves the basilar membrane, causing hairs to distort the hair cell and excite it. A very tiny movement (10-13 meters) activates the hair cells.
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The tonotopic organization
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responds to pitch. Place theory- different pitches distort the basilar membrane at different places. Higher pitches go to stiffer, left end, and lower to the looser, right end. At low pitches (under 200 hz especially), the frequency theory takes effect- stimulus is translated to the firing rate of nerve impulses and deforms the whole membrane equally. Middle pitches are a mix of the two.
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Acuity dilemma
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With vision, too many receptors would harm acuity. But the ear is different. While two ears give it some spatial representation, ears are mainly devoted to frequency analysis. Thus, acuity isn’t a problem, so many more than three sound receptor variations are allowed.
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