l11- hearing Flashcards
(25 cards)
what is sound
what is sound
- sound= change in local air pressure caused by vibrations of an object
- travels as a longitdual wave- particles move parallel to direction of wave
- sound can be trasnmitted, reflected or absorbed
what is sound
wave properties of sound
- amplitude: energy or power of the wave (relates to loudness)
- frequency: cycles per second (HZ), relates to pitch
- wavelength(λ)- distance between peaks of a wave
- speed(c)- distance sound travels per unit time
- period : time for 1 full cycle
- T=1/f,,,,,,,,,,,,,f=1/t
what is sound
wave equation
c= f.λ
- speed of sound in diff media:
- air (20C)=340m/s
- water=1500 m/s
- steel= 5000 m/s
- eg wl of 100Hz wave in :
- air= 3.4m
- water=15m
what is sound
sound vs light wave
similarities
similarities:
- both obey wave equation
- both can be reflacted, refracted n absorbed
- pure tone comparable to monochromatic light
- natural sounds n images compromise a spectrum of frequncies or WL
what is sound
sound vs light waves
differences
- medium:S= yes, L=no
- type: S=longtidual (parrellel), L=transverse (perpindicular)
- speed: S=slower (~340m/s in air)L=faster (~3x10^8m/s)
- classified by: S= frequncy (Hz)L=wavelength (nm)
- wavelength: S=1.7cm-17m, L=400-700nm
what is sound
fourier analysis
- complex sounds= multiple pure sounds
- fourier analyssi= decomposes complex sounds into sinusoidal components
- fourier spectrum= shows energy at each frequency
- fundamental frequency: lowest frequecny in a complex tone (determines pitch)
- timbre: related to harmonic structure
Basic structure of the auditory system
outer ear
- collects sound n enhances 2-6kHz
- protects the tympanic membrane (eardrum)
Basic structure of the auditory system
middle ear
- ossicles (malleus, incus, stapes) amplify sound
- acoustic reflex protects from loud, substained noise
- aimplification aids sound wave tavel through fluid filled chambers in inner ear
Basic structure of the auditory system
inner ear
- cochlea: spiral fluid-filled organ
- contains basilar membrane, organ of corti
- hair cells convert mechanical waves- neural signals
- tectorial membrane shears to stimulate stereocilia
Basic structure of the auditory system
inner ear: cochlea
- 3 canals: tympanic, vestibular, middle
- canals seperated by 2 membranes- reissners + basilar
Basic structure of the auditory system
inner ear: organ of corti
- sits atop the basilar membrane
- made of hair cells n auditory fiber dendrites
- converts movements of cochlear partition into neural signals
Basic structure of the auditory system
inner ears: hair cells
- like retinal photoreceptors- convert stimulus energy to neural energy
- fast n sensitive
- inner hair cells- 1 row, 3500
- outer hair cells: 3 rows, 10,500
Basic structure of the auditory system
inner ear: in cochlea- tectorial membrane
- produces a shearing movement in response to sound, stimulates the stereocilia causing hair cells to pivot
Basic structure of the auditory system
inner ear: stereociliar n tip links
- tipe links connect to stereociliar so hair cells bend together
- bendig of stereocilia opens ion channels cuasing depolarization
- auditory nerve fibers stimulated
- mechanoelectrical trsnduction
Basic structure of the auditory system
mechanoelectrical transduction
- mechincal sound vibrations turned into electrical neural signals
Basic structure of the auditory system
hair cells (ear) vs photoreceptors (eye)
- HC=14,000, PR=100mn
- Hc= immediate response (1-3ms), PR=slower (40ms)
- HC=immediate adaption, PR= slow adaption (30min)
- HC=depolarize, PR= hyperpolarize
- HC= 1 nanometer change can activate a hair cell, PR= 1 photon suffecient to activate a rod
sound encoding in the cochlea
amplitude (loudness)
- louder sounds cause:
- more membrane displacement
- more neurotransmitter release
- higher firing rate in auditory nerve fibres
Sound intensity and pitch
frequency (pitch)
- place code: location on cochlea relates to pitch-
- base: high frequencies
- apex: low frequencies
- outerhair cells: sharpen frequency tuning via feedback
- temporal code:neurons fire at a particular point in the cycle of a wave
- phase locking: neurons fire in sync w wave phase (up to ~1000hz)
- volley principle: multiple neurons share firing load for higher frequencies
auditory pathway
- auditory nerve
- cochealr nucleus
- superior olive: binaural input
- inferior colliculus
- medial geniculate nucleus (MGN)
- primary auditory cortex (a1)
- all regions show tonotopic organization
psychacoustics
- studies perception of sound
- equal loudness curves: diff frequencies percieved as louder or softer at same amplitude
- loudness ≠ intensity (logarithmic perception)- brain only recognises when proportional changes occur
- study of what diff sounds ‘sound like’
equal loudness curve
- percived loudness depends on frequency:
- 2 tones at equal amp may not sound equal loud
- 2 other tones at diff amps may sound equally loud
- percived loudness increases more slowly than intensity:
- double intensity ≠ double loudness
- similiar to vision
need to be at diff frequencies to sound same loudness
hearing loss-
conductive
cant get in ear
- ossicles lose mobility
- otis media: middle ear filled w mucus, osicles move less, less amplification, threshold raised by 50dB, common in kids
- otosclerosis: abnormal growth of ear bones, surgery needed
hearing loss-
sensorineural
in inner ear
- metabolic vs sensory (cochlear fluid enviroment Vs hair cell injury)
- diabetes, ototoxic drugs, viral infection, noise exposure, genetic mutations
- noise: outer+inner hair cell loss
- age: presbycusis
- over the age of 20 yrs cant hear 15,000Hz
age hearing loss term
presbycusis
