Hearing - Dr. Kazama PDF

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Dr. Kazama...

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Hearing (3/23/15) Properties of Sound Waves  Frequency – corresponds to our perception of pitch o Length of the sound wave; perceived as high and low sounds (pitch) o Low Frequency - low pitched sounds (long waves) o High Frequency – high pitched sounds (short waves)  Amplitude – corresponds to out perception of loudness o Height or intensity of sound wave; perceived as loud and soft (volume) o Low Amplitude – soft sound o High Amplitude – loud sounds  Complexity – corresponds to our perception of timbre o Perceived as sound quality or resonance o Simple – pure tone o Complex – mix frequency Sound Waves  Hearing is about sound waves and changes in air pressure that unfolds over time.  Air molecules moved at faster rate = increase Hertz; change from low to high pitch.  Sound waves – Changes in air pressure unfolding over time  Oscilloscope – An electronic laboratory instrument that traces a visible wave form  Amplitude – the intensity of amount of energy of a wave, reflected in the height of the wave, it determines volume  Frequency – the rate of vibration, or the number of sound waves per second; it determines pitch (highness or lowness of sound)  Decibels (dB) – measurement unit for sounds  Hertz – measurement unit of frequency  Intensity of some common sounds o 0 dB = threshold for just hearing o 20 dB = whisper o 85 + dB = risk of hearing loss  Prolonged exposure about 85 dB produced hearing loss  Example: subway train, jet plane, loud thunder, rock band  If you can’t talk over it, it’s potentially harmful o Humans can hear 20 – 20,000 Hz  Audition o This sense or act of hearing o What do we sense and perceive in the energy of a sound wave  The Ear o Outer Ear – sounds waves are collected  Pinna – visible outer ear on either side of your head; helps pinpoint and locate sound  Auditory canal – where sound travels to reach the eardrum o Middle Ear – sound waves are amplified

Ear Drum – (tympanic membrane) tightly stretched membrane that vibrates when hit by sound waves  Ossicles – three tiny bones (hammer, anvil, stirrup) that pick up eardrum vibrations, amplify them, and pass them along to the cochlea in the inner ear o Inner Ear – sound waves are transduced into coded neural messages.  Cochlea – a coiled, bony fluid filled tube through which sound waves are transduced into never impulses  Fluid here tell you where you are in space, can cause motion sickness  Semi-circular canals – fluid filled channels that help maintain balance by orientating the brain  Auditory Nerve – converged nerve cell fibers, send neural messages to the brain’s thalamus and auditory cortex in the temporal lobe  Outer duct – fluid flows from the oval window, runs to the tip of the cochlea, and then runs back again to end at the round window  Inner duct – fluid-filled tube sandwiched between the outgoing and incoming portions of the outer ducts  Basilar Membrane – hair cells with cilia on top of this, cause vibrations when fluid comes down, causes changes in hair cells, releases neurotransmitters to synapse with auditory neurons  Video – converting sound waves into neural signals Distinguishing difference in pitch o Based on location of hair cells that create the neural signal  Example: Medium pitched sound stimulates hair cells near tip of basilar membrane o Hair cells like carpet – spring back, but leave imprint for a little while Hearing loss o If auditory nerve is damaged o If hairs can’t spring back, no problem hearing loud sounds, but problems detecting softer sounds. o If ossicles were damaged o Conductive hearing loss o Sensory neuron hearing loss o Cochlear implant takes place of neurons o Hearing aide takes place of ossicles How old are your ears? o People hear range of frequency; depends on age o Why do high pitches go first?  High frequency detected at base of cochlea, all hair cells stimulated, often stimulated a lot of the time even with other frequencies, like walking in and out of doorways when area of carpet is a little moved up. High-pitched device drives teens from loitering spots o The “Mosquito” uses:  Outside of movie theaters  In high school parking lots after games 

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 In a mall to deter skateboarders  Apartment buildings o Supposedly, the noise can’t be heard by babies and animals, but only bothers people aged 12-20 years. Hearing loss is only one ear have trouble locating sound in space (stereophonic ability to hear) Tinnitus o Condition where patients hear noise in head / ear, mostly ringing, can be clicking, etc., not hallucination o Sometimes but not always accompanied by hearing loss o Objective tinnitus - when person performing exam would be able to hear the sound as well by listening, when more spasms in muscles of ear that cause clocking sound, really rare o Subjective tinnitus – only heard by patients, though damage to ear cells may be the cause. Localizing Sound Source o Ears on either side of the head gives us stereophonic hearing o Timing method – identify direction by sensing which ear is stimulated first23457; works most effectively for sound waves that cycle more slowly o Volume method – sensing which ear is stimulated more vigorously by sound, works for locating high frequency sound waves that are disrupted by heard o Sounds directly behind or in front of individual are difficult to localize Other auditory illusions: o Megurk Effect – vision alters perceived sound o Sound alters perceived vision o High to low? Low to high?  1 high to low  2 high to low  3 high to low  4 high to low o Everyone hear it differently – why? o Tritone paradox – ones contain both higher and lower frequency but brains have preference for which to listen to  Depending on our language from birth  Each time you hear it, you probably hear it the same way o Shepard Tone Illusion – continue raising tones as each one drops, but tones sound like they’re rising forever Other auditory illusions: o Convert song (including vocals) into piano soundtrack o “Stayin’ Alive” (midi piano); “Piano Man”; “All Star” o Hear lyrics, but have to know of song beforehand Can you trust your ears? o No!...