10 100 1000 10,000Frequency (Hz)
(high)(low)
020406080
100(loudest)
(quietest)
sound levelin decibels(dB)
can hear
can't hear
this line shows thequietest sounds youcan hear. At soundpressure levels belowthis line you can't hearthe sound.
10 100 1000 10,000
Frequency (Hz)
(high)(low)
020406080
100
(loudest)
(quietest)
sound levelin decibels(dB)
*
*
*
All points on this curve have the same perceived loudness as the standard (*)
All points on this curve have the same perceived loudness as the standard (*)
All points on this curve have the same perceived loudness as the standard (*)
EQUAL LOUDNESS CURVES
SUMMARY
Sound is variation in pressure
Frequency, pitchIntensity (SPL, “sound pressure level”), loudness, decibels
Timbre, harmonicsEqual loudnessHearing thresholds
pinna(external ear)
malleusincusstapes
little bones
oval windowtympanic membrane (ear drum)
leverage= 1.3 x
this section coiled upin the actual ear (cochlea)
(ossicles)}
areadecrease17 x
}
OUTER EAR MIDDLEEAR
INNER EAR
helicotrema
THE EAR
basilar membrane
top tube
middle tube
bottom tube
tectorial membrane
hair cells
vibrations pass down the top tube to theend (the HELICOTREMA) and thenback down the bottom tube.
helicotremaoval window
vibrates most tohigh frequencies(around 10 kHz)
vibrates most tomiddlefrequencies(around 1 kHz)
vibrates most tolow frequencies(down to around27 Hz)
LESS STIFFSTIFF
HIGH FREQUENCIES
LOW FREQUENCIES
hairs
hair cell
nucleus
fibre of 8th nerve (auditory nerve)
ACTION POTENTIALS TO BRAIN
Auditory system 13 - 5
SUMMARY
Outer, middle, inner ear
Oval window, round window, Basilar membrane, tectorial membrane, hair cells
PLACE THEORY (which fibres, labelled lines)Von Békésy (Nobel prize 1961)
1 - Travelling wave; stiffness varies2 - one place most active for a given frequency3 - Tonotopic code; coded as place
PERIODICITY THEORY (how they are firing, temporal code)1 - sound coded as pattern
vibrates most tohigh frequencies(around 10 kHz)
vibrates most tomiddlefrequencies(around 1 kHz)
vibrates most tolow frequencies(down to around27 Hz)
Evidence against place-- Missing fundamental-- which can be masked -- some animals have no basilar membrane
Evidence against periodicity-- cells can’t fire fast enough-- diplacusis
Evidence for place-- physiology(basilar membrane)(cells tuned for frequencies)-- masking
Evidence for periodicity-- multiple cells could do it-- phase locking of cells
Evidence against place-- Missing fundamental-- which can be masked -- some animals have no basilar membrane
Evidence against periodicity-- cells can’t fire fast enough-- diplacusis
Evidence for place-- physiology(basilar membrane)(cells tuned for frequencies)-- masking
Evidence for periodicity-- multiple cells could do it-- phase locking of cells
Temporal coding up to about 4,000 hz… but each spike takes about 2ms… therefore only up to around 500 hz…..
Temporal coding up to about 4,000 hz… but each spike takes about 2ms… therefore only up to around 500 hz…..
But could share it out over several cells One cell might only be able to follow every 4th cycle…..
… but others can share the task
Evidence against place-- Missing fundamental-- which can be masked -- some animals have no basilar membrane
Evidence against periodicity-- cells can’t fire fast enough-- diplacusis
Evidence for place-- physiology(basilar membrane)(cells tuned for frequencies)-- masking
Evidence for periodicity-- multiple cells could do it-- phase locking of cells
Evidence against place-- Missing fundamental-- which can be masked -- some animals have no basilar membrane
Evidence against periodicity-- cells can’t fire fast enough-- diplacusis
Evidence for place-- physiology(basilar membrane)(cells tuned for frequencies)-- masking
Evidence for periodicity-- multiple cells could do it-- phase locking of cells
Place theorysound coded as place
Periodicity theorysound coded as pattern
Duplicitybelow 1-4 kHz, coded by periodicityabove 1-4 kHz, coded by place
hairs
hair cell
nucleus
fibre of 8th nerve (auditory nerve)
ACTION POTENTIALS TO BRAIN
Auditory system 13 - 5
Auditory cortex
Auditory thalamus
Superior colliculus
Inferior colliculus
cochlea
Cochlear nucleus
Superior olive
The AuditorySystem
The AuditorySystem(sub-cortical route)
Cochlear nucleus
Superior olive
Inferior colliculus
Superior colliculus
Cells in primary auditory cortex: -- tonotopically arranged-- respond to more complex features (eg howler monkey calls)
primary auditory cortex
Auditory localization
1 inter-aural time of arrival differences-- circle of confusion
2 inter-aural intensity differences3 pinnae (up/down front/back etc..)4 head movements