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PSYCH 1XX3 (384)
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Chapter 11

PSYCH 1XX3 Chapter 11: Module 11- Audition

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Joe Kim

Module 11- Audition The Auditory Mechanisms of Different Species - The mechanisms differ among species according to the specific needs o Water or air o Need to communicate over long distances o Receive high or low frequency sounds - Form through the process of evolution - One way that hearing abilities differ is through frequencies o Dog whistle o Produces a high frequency sounds that is beyond the range of a human but dogs within the auditory system of a dog - Humans can perceive anywhere from 20-20,00 Hz - Whales, dolphins and dogs have a wider hearing range - Frogs and birds have a narrower hearing range - At the lower extreme are fish - At the higher extreme are bats and rodents - Audible frequency range is determined in part by the evolution of the structures of the auditory system - Basilar membrane: contains the hearing receptors, sounds of different frequencies are processed along different areas of the membrane o Varies in length between species o Shortest in amphibians and reptile o Longest in mammals o A longer membrane allows for a wider range of frequencies Sound Waves - Sound travels in waves - Waves are initiated by either a vibrating object or a by forcing air past a small cavity - The chain reaction is like ripples - Alternating bands of more and less condensed air particles that travel away from the source are like the ripples observed in a pond - The alternating bands of more and less condensed air particles interact with the eardrum to begin auditory processing o More dense air causes the eardrum to go slightly inwards o Less dense air causes the eardrum to go slightly outwards - The changes in air pressure over time that make up a sound wave can be graphed as sine waves - Three characteristics are observed o Amplitude: loudness o Wavelength: pitch o Purity: timbre - Amplitude: Loudness o Variation in amplitude (or height) od a sound wave affect the perception of loudness o Since waves of a greater amplitude correspond to vibrations of greater intensity, higher waves correspond to louder sounds o Measured in the logarithmic scale of decibels (dB) - Frequency: Pitch o Distance between peaks is called frequency which affects the perception of pitch o Pitch is measured in Hz which represents the number of cycles per second o If may waves peak in one second the sound will be high frequency and give the perception of a higher pitch - Purity: Timbre o Single frequency vibrations are called simple sounds o Most everyday sounds are composed of multiple sound waves and are considered complex o Timbre refers to the complexity of a sound The Ear - The external ear is made up of the pinna, the ear canal and the eardrum - The pinna is the ear itself (or what you first think of when you think of an ear) it is the folded cone that collects the sound waves - The ear canal is the pathway that connects the eardrum from the outside world - The eardrum functions to amplify the incoming waves much like a horn. The eardrum is a think membrane vibrating at the frequency of the incoming waves - The ear can be divided in to external, middle and inner ear - The middle ear beings on the other side of the ear drum, which connects the ossicles (three smallest bones in the body) o Hammer o Anvil o Stirrup - The amplification of the vibrating waves continues in the middle ear - The additional amplifications are necessary because the changes in air pressure originally indicated by the external ear are about to be converted to waves in the fluid filled inner ear - The vibrating oval window connects the cochlea of the inner ear - The cochlea is a fluid-filled tube about 35mm long, coiled like a snail shell - The cochlea contains neural tissue that is necessary for the transfer of fluid of neural impulse of audition - Inside the cochlea is a flexible membrane called the basilar membrane - So when the membrane is pushed downward it causes the wind
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