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Psychology (4,979)
PSYCH 1XX3 (1,043)
Joe Kim (962)


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Joe Kim

Audition Hypotheses 1. Sound is product of external stimulus (tree falling in forest would make noise but no one would hear it) 2. Sound is the result of our own sensory processing (if no one was there to hear the falling tree, then the tree would not make a sound at all) Sound Waves and Auditory Systems • Auditory systems can translate sound waves from vibrating objects into the psychological experience of audition • Sound waves would be produced • Sound is the result of our interpretation of wave The Auditory Mechanisms of Different Species • Auditory mechanisms vary across different species according to different needs o Live in water, land or air o Whether they need to communicate over long distances o Whether they need to be able to receive high or low frequency sounds Sound Frequency • Range of frequencies differ across species • The dog whistle example o Produces sound at high frequency - over range of human ears but dog can hear it • Humans can perceive sound between 20-20 00 Hz • Wider hearing range  Whales, dolphins and dogs • Narrow hearing range  Frogs and birds • Lower frequency  fish • Higher frequency  bats and rodents Environmental Impacts on Auditory Structure • Audible frequency range is determined by the evolution of the structures of the auditory system • Key structure – basilar membrane o Contains hearing receptors o Sounds of different frequencies are processed along different areas of the basilar membrane The Basilar Membrane • Varies in length across species • Shortest  amphibians and reptiles • Longer birds • Longest  mammals o Longer basilar membrane  wider range of frequencies o Mammals discriminate the widest range of frequencies o Most other species cannot discriminate frequencies over 10,000 Hz The Stimulus: Sound Waves • Stimulus ears and brain are processing is the sound waves • Like light, sound travels in waves o Sound travels slower o Sound waves require some medium to travel through • Sound waves are initiated by either a vibrating object (vocal cords/guitar string) or a sudden burst of air (clap/pipe organ) o Result – air molecules surrounding source of sound are forced to move o Causes a chain reaction of moving air particles Responding to Changes in Air Pressure • Chain reaction like ripples when you throw stone in pond • Stone hits the pond – produces waves that travel away in all directions o Like, alternating bands of more and less condensed air particles that travel away from the source of a sound The Eardrum Responds to Air Pressure Changes • Alternating bands interact with the eardrum to begin auditory processing • A band of compressed air molecules causes eardrums to get pushed slightly inwards • Whereas a band of less dense air particles causes the eardrum to move slightly outwards Sine Waves • Changes in air pressure over time that make up a sound wave can be graphed into a sine wave • Three physical characteristics of a wave o Amplitude o Wavelength o Purity • Can be translated into three psychological properties o Loudness o Pitch o Timbre Amplitude: Measures of Loudness • Variations in amplitude/height of a sound wave affect perception of loudness • Greater amplitude  vibrations of greater intensity o Higher waves  louder sounds • Humans sensitive to a wide range of different sound amplitudes – thus, loudness measured using a logarithmic scale of decibels (dB) o Perceived loudness of a sound doubles for every 10 dB increase • Examples o Conversation = 60 dB o Whisper = 27 dB o Sitting in the front row at a rock concert = 120 dB  Brief exposure can cause physical pain and permanent damage Frequency: Measure of Pitch • Frequency/wavelength – distance between successive peaks • Property affects pitch • Pitch measured in Hertz (Hz) o Represents number of cycles per second/number of times in a second that a sound wave makes one full cycle from one peak to the next • If many peaks are condensed into one second – the sound will be of high frequency (draw diagram high frequency vs. low frequency) o Result in the perception of a high pitched sound • The audible zone of frequencies that humans can detect represents only a portion of the possible frequencies that can be produced Timbre: Measure of Complexity/Purity • Purity - affects perception of timbre • Timbre – complexity of a sound o Most of the sounds we hear every day are complex sounds that are composed of multiple sound waves that vary in frequency • Example – Guitar o Pluck guitar string, vibrates whole – fundamental tone o Also vibrates shorter segments along the string – overtones o Final sound is a mixture of the fundamental tone and all the overtones  Combination is timbre • Bassoon and piccolo both play the same note but each instrument produces unique combination of the fundamental frequency and overtones o Sound different even though each instrument is producing the same frequency and amplitude The Ear • Instrument used to detect sound waves and convert them into something that the brain can interpret The Structure of the Ear • Divided into external, middle and inner ear - each area conducts sound in a different way o Incoming changes in air pressure are channelled through the external ear o Onto the middle ear and amplified so that it can be detected as changes in the fluid pressure by the inner ear o Changes in fluid pressure are then converted to auditory neural impulses The External Ear • Made up of the pinna, the ear canal and the eardrum • Pinna - what one thinks of when one refers to ears o Folded cone that collects sound waves in the environment and directs them along the ear canal • Ear canal narrows as it moves towards the eardrum o Functions to amplify the incoming sound waves (like a horn) • Eardrum – thin membrane vibrating at the frequency of the incoming sound wave o Forms the back wall of the ear canal The Middle Ear • Begins on the other side of the eardrum o Which connects to the ossicles - the 3mallest bones in the body • Ossicles are named after appearance • Consists of the hammer, anvil and stirrup Ossicles Amplify Signal Sent to the Oval Window • Middle ear - amplication of the vibrating waves continues • Vibrating ossicles are about 20 times larger than the area of the oval window to which they connect to create a lever system that amplifies the vibrations more • Additional amplification necessary because the changes in air pressure originally detected by the external ear are about to be converted to waves in the fluid filled inner ear The Inner Ear • Vibrating oval window connects to the cochlea of the inner area • Cochlea – fluid-filled tube about 35mm long, coiled like a snail o Contains neural tissue that is necessary to transfer the changes in fluid to neural impulses of audition The Cochlea • Oval window - small opening in side of the cochlea • When oval window is made to vibrate  causes the fluid inside the cochlea to become displaced • Round window o Located at the other end of the cochlea o Accommodates for the movement of the fluid by bulging in and out Basilar Membrane • Inside the cochlea is flexible membrane – basilar membrane o Runs the length of the cochlea (like a carpet) • Basilar membrane is pushed downwards  the fluid inside the cochlea causes the round window to bulge out • Basilar membrane is forced upwards  the round window bulges inwards • Cochlea gets narrower towards the end • Basilar membrane gets wider towards the end o Length varies in flexibility and width  sounds of different frequencies cause different regions of the membrane to vibrate  Higher frequency sounds  end nearest to oval window to vibrate  Lower frequency sounds  end nearest the round window to vibrate Hair Cells • Basilar membrane houses the auditory receptors – called hair cells • Membrane moves in response to waves in fluid, hair cells also move o Hair cells movement converted to neural impulses that the brain can understand Auditory Pathway – From Receptors to Auditory Cortex Introduction to Auditory Pathway • When activated, hair cells along basilar membrane release a neurotransmitter • Hair cells form synapses with bipolar cells (whose axons make up the cochlear nerve - a branch of the main auditory nerve) • Outer hair cells outnumber the inner hair by about 4 to 1 • Inner hair cells mainly contribute to the signal in the cochlear nerve Cochlear Nerve and Hair Cells • Outer hair cells o Share one direct link to the brain o With 30 other outer hair cells o More numerous but faster o Axons that synapse with out
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