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Audition Module.doc

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McMaster University
Joe Kim

Audition Module Auditory Mechanisms Through Evolution: o If a tree falls and there is no one to hear it will it make a sound that humans can not pick up. -We know if a tree falls it will produce molecules of condensed air and sound waves, which can not be interpreted without an auditory mechanism present. o A dog whistle produces sound at a very high sound o Humans can hear 20 – 24 Hz. The Basilar Membrane o Sounds of Different frequencies are processed at different areas of the basilar membrane. o Longer = being able to distinguish between a wider range of frequencies. Sound Waves: o Sound waves are slower than light waves and require some medium to travel to o Sound waves are initiated by sudden burst of air or vibration. o The air particles around the source of the vibration are strongest and promote a ripple effect. e.g. such as throwing rock in water. o These particles interact with the eardrum. o A band of compressed air particles causes ear to move inwards o A band of less compressed air particles causes ear drum to move outwards. o Three Aspects of Sine Waves  1. Loudness: Variations in amplitude effects the perception of loudness. -Higher waves = louder sounds -Loudness is measured by dBs -e.g. Normal Conversation is 60dB, Rock Concert is 120 dB  2. Pitch: Distance between successive peaks -Measure in Hz, measures one peak to the next. - Higher peaks = high pitched sound.  3. Purity/Tibmre: Most sounds we hear are comprised of multiple sound waves. e.g guitar string gives off one solid sounds of vibration of the string as well as shorter wave lengths of sound near the beginning of the strong. -Combination of this sound = timbre. - Two instruments can be playing same sound however but because each has different over tones they sound different even with same frequency and amplitude. The Ear: o The ear can be divided into three areas. o Incoming changes in air pressure is brought into outer ear then middle ear and then fluid pressure are found in inner ear where they are made into neuro signals.  1. External Ear: -Pinna is the folded cone which collect incoming sound waves -Ear drums amplify sounds -Says that elements close together in space tend to belong together.  2. Middle Ear: Starts after eardrum connect to the ossicles which are the tinniest bones in the body. -They are called hammer, anvil and strirrup. -Amplification of the vibrating waves continues here because these waves first detected in a different air pressure are going to be detected in a fluid filled inner ear. - Cochlea contains fluid required to detect and transfer these waves into neuro-impulses. -Oval window is a small opening in the side of the cochlea and when its made to vibrate it causes the fluid inside cochlea to become dispersed -The overall window is located at the other and accommodates the fluid by bulging in or out. -Inside the cochlea is a flexible membrane called the basilar membrane. When the basilar membrane is pushed upwards the round window is forced to move inwards and vise versa. - The basilar membrane gets wider near the end. -Lower frequency sounds causes the end near the coclear to vibrate. -Higher frequency sounds nearest the round window to vibrate. o Hair cells cause neural impulses as they move. o Incoming changes in air pressure is brought into outer ear then middle ear and then fluid pressure are found in inner ear where they are made into neuro signals. Auditory Pathway: From Receptors to Auditory Cortex o When activated the hair cells on the basal membrane produce neural impulses. o The hair cells form synapses with bi-polar cells. o These axons make up the cochlear nerve, a branch of the main auditory nerve. o
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