1 Brain and Behavior Exam 3 Lecture 11 Audition 7 1 1 What are amplitude and loudness frequency and pitch Amplitude intensity of a sound wave height Ex a bolt of lightning produces sound of great amplitude Loudness Perception of intensity related to amplitude but not identical to it Ex a rapidly talking person sounds louder than slow music of the same physical amplitude if you complain a television commercial is louder than the program it is because the people in the commercial are talking louder A higher amplitude results in a louder sound Frequency Number of compressions per second measured in hertz Pitch Perception of frequency The higher the frequency the higher the pitch 2 Know the functions of the parts of the ear Know what part of the ear they are in outer middle inner Consist of Outer ear 1 Pinna also called auricle The familiar structure of flesh and cartilage attached to each side of the head By altering the reflections of sound waves the pinna helps us to locate the source of a sound We have to learn to use that information because each person s pinna is shaped differently It funnels sounds from the outer to middle ear 2 External Auditory Canal Middle Ear 1 Tympanic Membrane also called the eardrum Receives sound wave through auditory canal It vibrates at the same frequency as the sound waves that strike it Connects to three tiny bones that transmit the vibrations to the oval window 2 Ossicles The 3 tiny bones in the tympanic membrane Hammer Malleus Anvil Incus and stirrup stapes Transform waves into stronger waves amplification Work as levers by compressing force Stronger waves go to the oval window a membrane in the inner ear Inner ear 1 Oval Window Membrane that transmits waves through the viscous fluid of inner ear Receives information from tiny ossicles The stirrup which connects to the oval window causes it to vibrate and sets in motion all the fluid in the cochlea 2 Cochlea A snail shaped structure with 3 long fluid filled tunnels the scala vestibuli scala media and scala tympani Involved in transduction 3 Hair cells The auditory receptors that lie between the basilar membrane of the cochlea on one side and the tectorial membrane on the other Vibrations in the fluid of the cochlea displace the hair cells which excite the cells of the auditory nerve 2 3 How does a hair cell work What ion enters the hair cell from the endolymph What leads to neurotransmitter release Vibrations in the cochlea displace the hair cells A hair cell responds within microseconds to displacements as small as 10 10 meter thereby opening ion channels in its membrane The hair cells excite the cells of the auditory nerve which is part of the eighth cranial nerve 4 What is the sequence of events from the sound wave entering the external auditory canal to the hair cell being stimulated Pinna sound waves external auditory canal tympanic membrane eardrum vibrates connects to Ossicles 3 bones stirrup bones transmit vibrations to oval window transform into stronger vibrations force moves viscous fluid to cochlea auditory receptors hair cells between membranes displaced by vibrations thereby opening ion channels in its membrane hair cells excite auditory nerve AP Auditory Nerve is sent to brainstem 5 What is the pathway that auditory information takes in the brain What aspect of processing does each of those regions do Auditory nerve cochlear nucleus pons localization midbrain Inferior Colliculus orients and integrates with visual thalamus sensory integration filter relay auditory cortex temporal lobe The cochlea nucleus receives input from the ipsilateral ear only the one on the same side of the head All later stages have input originating from both ears 6 Understand the term tonotopic and how it is relevant to the cochlea and the cortex The tonotopic map is within the primary auditory cortex area A1 Cells in this area respond to tones of particular frequency Neurons are arranged in a gradient with cells responding to low frequency tones at one end and cells responding to high frequency tones at the other end Tonopy begins at the cochlea which sends information about sound to the brain The auditory nerves that transmit information from different regions of the basilar membrane therefore encode frequency tonotopically This is maintained in the human vestibule cochlea nerves cortex the part of the brain that receives and interprets sound information 7 Understand the terms place theory frequency matching 8 How do we localize sounds 3 Place Theory each area along the basilar membrane has hair cells sensitive to only 1 specific frequency of sound wave resembling the strings of a piano Each frequency activates the hair cells at only one place along the basilar membrane and the nervous system distinguishes among frequencies based on which neurons respond The downfall is that the parts of the basilar membrane are bound together too tightly for any part to resonate like a piano string High frequency sounds displace base of basilar membrane Low frequency sounds displace apex of basilar membrane and therefore it is best for high frequency sounds Frequency theory the basilar membrane vibrates in synchrony w sound causes auditory nerve axons to produce action potentials at same frequency Hair cells fire at same rate as frequency of sound 200 Hz sound 200 AP s per sec by apex Only works up to 250 Hz which is the maximum rate neurons can fire action potentials because of the refractory period of the axon and therefore is best for low frequency sounds Determining the direction and distance of a sound requires comparing the responses of the two ears One cue for sound location is the difference in intensity between the ears For high frequency sounds with a wave length shorter than the width of the head the head creates a sound shadow making the sound louder for the closer ear Produces accurate sound localization for high frequencies above 2000 to 3000 Hz A second cue is the difference in time of arrival at the two ears A sound coming directly in front of you reaches both ears at once Sounds from the side reach the closer ear at about 600 microseconds before the other Sounds coming from intermediate locations reach the two ears at delays between 0 and 600 microseconds Time of arrival is most useful for localizing sounds with a sudden onset A third cue is the phase difference between the ears Every sound wave has 2 consecutive peaks 360 degrees apart If a sound originates to the side of the head the sound wave
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