S P Exam 4 Study Guide Ch 9 10 12 Chapter 9 Hearing Physiology and Psychoacoustics Basic Qualities of Sound Waves Frequency and Amplitude o Amplitude Intensity The magnitude of displacement increase or decrease of a sound pressure wave Amplitude is perceived as loudness Decibel dB a unit of measure for the physical intensity of sound Define the difference between two sounds as the ratio between two sound pressures Each 10 1 sound pressure ratio 20 dB 100 1 ratio equals 40 dB o Frequency For sound the number of times per second that a pattern of pressure change repeats Frequency is perceived as pitch o Hertz Hz a unit of measure for frequency One hertz equals one cycle per second Psychological Qualities amplitude o Loudness the psychological aspect of sound related to perceived intensity o Pitch the psychological aspect of sound related mainly to perceived frequency Sine Waves and Complex Sound o Sine Wave Pure Tone a waveform for which variation as a function of time is a sine function o Complex Sounds All sounds even as complex as sounds by instruments human speech etc can be described as a combination of sine waves Best described in a Spectrum a representation of the relative energy intensity present at each frequency Displays how much energy or amplitude is present at multiple frequencies Sounds with Harmonic Spectra are typically caused by a simple vibrating source such as the string of a guitar frequencies Basic Structure of the Mammalian Auditory System o Outer Ear Pinna Ear Canal Harmonic Spectrum the spectrum of a complex sound in which energy is at integer multiples of the fundamental frequency Fundamental Frequency the lowest frequency component of a complex periodic sound Timbre the psychological sensation by which a listener can judge that two sounds with the same loudness and pitch are dissimilar o Timbre quality is conveyed by harmonics and other high Sounds are first collected from the environment by the pinna Pinna the outer funnel like part of the ear o Curly structure on the side of the head o Typically called the ear o Only mammals have this Sound waves are funneled by the pinna into and through the ear canal which extends about 25 mm into the head Ear Canal the canal that conducts sound vibrations from the pinna to the tympanic membrane o Main purpose protect tympanic membrane Tympanic Membrane the eardum a thin sheet of skin at the end of the outer ear canal o Vibrates in response to sound COMMON MYTH puncturing your eardrum will NOT leave you deaf Possible to damage beyond repair o Middle Ear Middle Ear an air filled chamber containing the middle bones Conveys and amplifies vibration from the tympanic membrane to the oval window Tympanic Membrane is the border between the outer and middle ear Consists of three tiny bones the ossicles that amplify sound waves Ossicle any of three tiny bones of the middle ear o smallest bones in the human body o Amplify sound vibrations in two ways The joints between the bones are hinged in a way that makes them work like levers a modest amount of energy on one side of the fulcrum joint becomes larger on the other This lever action increases the amount of pressure change by about a third Concentrating energy from a larger to a smaller surface area the tympanic membrane to the oval window o Malleus receives vibration from the tympanic membrane and is attached to the incus o Incus middle of the ossicles conntecting the malleus and the stapes o Stapes connected to the incus on one end the stapes pressed against the oval window of the cochlea on the other end o Oval Window the flexible opening to the cochlea through which the stapes transmits vibration to the fluid inside Middle ear has two muscles Smallest muscles in the body Main purpose to tense when sounds are very loud restricting the movement of the ossicles and thus muffling pressure changes that might be large enough to damage the structures in the inner ear Tensor Tympani muscle attached to the malleus tensing the tensor tympani decreases vibration Stapedius muscle attached to the sapes tensing the spaedius However this acoustic reflex follows the onset of loud sounds decreases vibration by one fifth of a second o Acoustic Reflex a reflex that protects the ear from intense sounds via contraction of the stapedius and tensor tympani muscles NOT READY FOR ABRUPT SOUNDS o Inner Ear Function similar to the retina waves into neural signals Translates the information carried by Major structure of the inner ear is the Cochlea Cochlea a tiny coiled structure embedded in the temporal bone of the skull o Contains the organ of Corti o Uncoiled would be about 35 mm long o Filled with watery fluids in three parallel canals Tympanic Canal extends from the round window at the base of the cochlea to the helicotrema at the apex Vestibular Canal extends from the from the oval window at the base of the cochlea to the helicotrema at the apex Middle Canal sandwiched between the tympanic and vestibular canals and contains the cochlear partition Helicotrema the opening that connects the tympanic and vestibular canals at the apex of the cochlea o Three canals of the cochlea are separated by two membranes Reissner s Membrane a thin sheath of tissue separating the vestibular and middle canals in the cochlea Basilar Membrane a plate of fibers that forms the base of the cochlear partition and separates the middle and tympanic canals in the cochlea Cochlear Partition the combined basilar membrane tectorial membrane and organ of Corti which are together responsible for the transduction of sound waves into neural signals Complex structure Vibrations transmitted through the tympanic membrane and middle ear bones cause the stapes to push and pull the flexible oval window in and out of the vestibular canal at the base of the cochlea This movement causes waves of pressure changes traveling waves to flow through the fluid in the vestibular canal Because the cochlea is a closed system the pressure changes cannot spread out in all directions Instead a displacement forms in the vestibular canal and travels from the base of the cochlea down to the apex By the time they reach the apex its displacement has mostly dissipated If extremely intense sounds remaining pressure is transmitted through the helicotrema and back to the cochlear base through the tympanic canal where it is absorbed by stretching another membrane called the round window o Round Window a soft area of tissue at the base of the tympanic canal