PY2507.1 ~ {Communication by sound}1.0
what is the speech chain?
process through which speech sounds are produced + transmitted + perceived: it involves several stages covering the entire. cycle of communication
the speech chain levels
linguistic + physiological + acoustic + physiological + linguistic [level] - the diff forms of a spoken message in its progress fro the brain of the speaker to the brain of the listener
the ear
outer ear comprises the pinna + ear canal + eardrum
where p - important for sound localization + ec - has a broad resonance that amplifies freq around 3kHz
freq range of human hearing
[a young adult]
20Hz to 20kHz
alternative names
external ear - pinna + ear canal - external auditory meatus + eardrum - tympanum / tympanic membrane + auditory nerve - cochlear nerve
computer metapor
for human mind, key issues involved: encoding + storing + retrieval + maniupulation of info [verbal: spoken or written lang & non-verbal: images / space / action]
route of the speech chain [speaker]
starts with intent of the talker to convey some info to listener [at linguistic level] then the physiological level, this process generates sound waves into the acoustic level
speech chain speaker linguistic level
involves chosing appropriate words + arranging them in suitable order
speech chain speaker physilogical level
we have to move our vocal organs [involved in speech production] in a particular way this process generates sound waves
what is sound
vibrations in the air + very rapid changes in air pressure
function of ear
to convert sound into an electrical response
transduction
the process by which sensory stimuli are converted into neural signals that can be interpreted by the brain. It involves the transformation of physical energy (such as light, sound, or pressure) into electrical signals that can be transmitted through the nervous system.
why are there 2 ears shown on speech chain
we monitor our own speech and use info to keep adjusting + refining our speech production; used as a control of speech production
what proof do we have to justify that we listen to ourself as a control for speech production [disabled]
in individuals who are deaf they tend to showcase a detereoration in they speech production cause the system thats meant to be helping them monitor this is faulty
what proof do we have to justify that we listen to ourself as a control for speech production [not disabled]
using delayed speech: if you have a voice played back to you with a delay of half a sec it radically interrupts the process of speech generation [cause of the lack alignment between what you're hearing and what you think you should be hearing]
3 distinct regions of the ear
outer middle and inner
what does the outer ear comprise of
[aka the external ear] pinna [flappy bit] + ear canal + eardrum
movement of sound into ear
sound travels through the air, reaches the head and collected by exteranl ear the funneled down ear canal to reach ear drum
shape of pinna
its very important in our ability to localise sound so the scrolls and shapes they filter the sound slightly differently when it comes from diff directions the cues that are present are used by your brain to localise the source of the sound in space
middle ear
an airfield chamber [its got air in it] right behind your eardum
its connected to our throats through a tube known as the eustachian tube [when we yawn or swallow this tube is involved]
inner ear
entrance known as oval window, inner ear is full of fluid [has 2 distinct regions: vastipular system important for balance and the cochlea]
what is freq range for human hearing
[young adult] 20Hz - 20kHz
ear canal resonance
is broad and amplifies freq arounf 3kHz
hertz
cycles per second of vibration
bones in middle ear
malleus + incus + stapes = hammer + anvil + stirrup [alltogether ossicles] increase efficiency for sound to get from air into the fluid
impendence matching
length of the hammer is 15% larger than anvil to help function as lever system, ratio of eardrum to oval window is 35:1 which leads to effective increase in sound transmission = 38dB
protective reflex
to help protect you from damage of very intense sounds: the stapedius muscle contracts + stiffens the chain of ossicles when the ear is exposed to intense sounds [doesn't work very well for impulsive sounds like gunshots]
cochlea partition
membranous structure that divides cochlea along its length, the hollow interior of the partition is called the cochlear duct
cochlear duct
made up of vestibular canal + tympanic canal + scala media and they're all filled with lymph fluid
human cochlea
has 2.75 turns from base to apex + about 3.5cm long if uncoiled
how does sound get into cochlea
flapping movement of stapes at oval window that pushes sound in system, when it pushes up it increases pressure in the chamber and cochlear partition gets pushed up the - helicotrema [hole at the end]
the basilar membrane
separates the cochlear duct for scala tympani
the part of this next to oval window is called basal or stapedial end whilst the one furthest away is called apical / helicotremal end
freq response of cochlea
basilar membrane repsonds best to low freq at apical end where it is widest (.5mm) + heaviest + least stiff as well as high freq at basal end where it is narrowest (.04mm) lightest + most stiff [x100 stiffer than apex]
who did pioneering research on basilar membrane mechanics
George von Békésy in 1950s [american hungarian]
using strobe illumination of silver paticles in ears of human cadavers [corpses]
organ of corti hair cells
2 types inner + outer
i - 1 row, sensorycells that respond to movement of basilar membrane
o - 3-5 rows, affect how basilar membraan emoves in response to sound [sharpening our ability to discriminate freq of sound]
neural transduction
inner hair cells capped with stereocilia [hair bundle] where cells synapse onto auditory neurons + displacement og hair bundle changes membrane potential and stretched tip links between adjacent tereocilia [causes depolarization] + this causes NT release that excites postsynaptic auditory neurons
auditory nerve
spiral ganglion contains cell bodies of auditory neurons + axon of these are bundled together in modiolus [hollow core of cochlea]
how many axons does auidtory nerve have
about 28 000 [in humans]
anatomical evidence on auditory nerve
suggests that each axon has synoptic connections with inner cells only at one place along the basilar membrane which implies responses of each auditory neuron will be freq selective [place code]
how does the speech chain go
starts in the brain