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Sensation _ Perception - lecture 15 - the auditory system and basic auditory functions

Sensation _ Perception - lecture 15 - the auditory system and basic auditory functions

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The Auditory System and Basic Auditory  Functions
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“It has been said that a blind person is cut off from the  world of things, whereas one who is deaf is cut off  from the world of people.”
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What is Sound? The Auditory Stimulus = sound waves. Sound wave frequencies are measured in Hertz (Hz). 1 Hz = 1 cycle per second. Audible Sound = a pressure wave with frequency  between 20 Hz and 20,000 Hz and with an intensity  above the standard threshold of hearing. As we age we become less sensitive to higher frequencies. Ratio between faintest sound detectable and the loudest sounds  that don’t cause serious damage is more than one to a million.
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What is Sound? Basic Physical Qualities of Sound Waves Amplitude = magnitude of displacement (increase or decrease)  of a sound wave. Frequency = number of times per second a pattern of pressure  change repeats. Range of audible sounds = 20 Hz to 20,000 Hz. Most sensitive to sounds from 1,000 to 4,000 Hz. Weber Fraction is much smaller compared to other senses.
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What is Sound?
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What is Sound?
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What is Sound? Phase Angle The angle at each position in the cycle of a sound wave. 0 degrees = normal air pressure. 90 degrees = maximal air pressure. 180 degrees = return to normal air pressure. 270 degrees = minimum air pressure.
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How Does Sound Occur? Normal Atmospheric Pressure
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How Does Sound Occur? Sound waves are created when an object vibrates in  an elastic medium. Elastic Medium   liquids, ground, metals, wood, and AIR. Vibrations displace molecules causing pressure  changes in the medium. Speed at which sound waves travel depends on the  medium… Move faster through denser substances.
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Since we possess such a broad range of detectable  sounds, they are measured on a logarithmic scale in  decibels . Decibels define the difference between two sounds in terms of  the ratio of sound pressures. Each 10:1 pressure ratio = 20 dB … a ratio of 100:1 = 40 dB. dB = 20 log(p/po)  p = sound pressure po = reference pressure (fixed value) In logarithmic scales, small changes correspond to relatively  large physical changes. Measuring Sound
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Measuring Sound
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How Do We Perceive Sound? Pure Tones vs. Complex Tones Simplest kind of sound is a sine wave, referred to as a pure  tone. Pure tones are rare … almost all sounds (or noise) are complex  tones.
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