Transcript Speech Science XI

Version WS 2007-8
Speech Science XI
Speech Perception
(auditory physiology)
Topics
• What activity does speech perception imply?
• The physiology of hearing
• Reading: BHR, Chap. 6, pp. 174ff 3rd ed.
Ch. 9, pp. 201ff 5th ed
(The listener, hearing, the ear)
Kent, Chap. 6, pp. 209 ff.
P.-M., 3.1.1-3.1.3 pp. 143-149
(physiologische Grundlagen)
What is Perception?
• Dictionary definition:
"The process, by which an Organism detects and
interprets Information from the external world by
means of the sensory receptors" (Collins English
Dictionary)
but also:
• "Sinnliche Wahrnehmung eines Gegenstandes
ohne bewußtes Erfassen und Identifizieren"
(Duden: Das große Wörterbuch der deutschen
Sprache)
What is Perception?
• In terms of Semiotics: Perception is the recognition
of patterns (forms) which are important for our
(personal) life. I.e., forms which have a meaning for
us (= Signs).
• Auditory Perception is the part of our pattern
recognition mechanism dealing with acoustic input.
What other perception mechanisms do we have?
• Speech perception is the aspect of our auditory
perception which identifies the patterns which are
relevant to speech in the (often mixed-up) acoustic
signals which reach our ears.
Are there other auditory perception subsystems?
Auditory Physiology
• All auditory perception is served by the same input
channel at the auditory periphery:
The outer ear (receives the acoustic signal and
transforms it to mechanical vibrations)
The middle ear - strengthens the mechanical signal
and transfers it to:
The inner ear, which transforms the mechanical
signal to an electric signal (nerve impulses which
travel to the brain).
• “Audition” is the term for these peripheral
processes
Anatomy
of the Ear
Outer Ear
• The part of the outer ear we can see is called
“pinna” or “auricle“
• The auditory channel or “external auditory meatus”
leads from the outside to the middle ear.
It is a tube with a diameter of about 0.6 cm and a
length of between 2.5 and 3 cm.
This acts as a resonator for frequencies around
3 kHz. (they are heard as louder)
• The ear drum is a membrane that separates the
outer ear from the middle ear.
The acoustic signal causes the membrane to vibrate.
Eardrum
•
Middle Ear 1
Here we see the position
of the three bones which
strengthen the mechanical
signal produced by the
eardrum and transfer it to
the inner ear via the oval
window.
The malleus (hammer) is
attached to the eardrum
by the manubrium (handle)
and vibrates with it. The
vibrations are passed on
to the incus (anvil) and
from there to the stapes
(stirrup). The „footplate“
of the stiirup is attached
to the „oval window“, a
membrane separating the
middle ear from the inner
ear.
Middle Ear
Malleus
Middle Ear 2
The bones in the
human ear are
the smallest bones
in the body:
The hammer:
(Malleus)
5.5 mm
The anvil:
(Incus)
5 mm
The footplate
of the stirrup:
(Stapes)
3.2 x 1.4 mm
Incus
Stapes
Middle ear amplification
Inner Ear
oval
window
round
window
Scala
Scala
media
Scalamedia
media
Scala vestibuli
Scala tympani
The inner ear has two
functional components:
The vestibular system
for balance (the semicircular canals) and the
auditory system (the
cochlear).
The cochlear is divided
lengthways by two membranes into three sections:
The scala vestibuli, scala
media and scala tympani.
helicotrema The membrane of the oval
window vibrates with the
stapes and send waves
down the s.vestibuli. At
the end of the s.vestibuli,
they pass into the s. tympani
via the helicotrema, and
are damped by the round
window
Scala tympani
Scala media
Scala
vestibuli
Inner Ear 2
Travelling waves in the scala
vestibuli make the Reissner‘s
membrane vibrate, transferring
vibrations to the Organ of Corti
on the Basilar membrane.
The Organ of Corti has fine
Above: Section through the cochlear showing
hair cells which, when disturbed
the three scalae. Below: a magnified cross section
by the vibrations, produce small
at one point in the cochlear.
electrical discharges.
This is the stage at which the
Reissner‘s membrane originally acoustic signal enters
the nerve system.
Scala
The electrical discharges from
vestibuli
Basilar
S. media
membrane
the hair cells transfer to the
with Organ
auditory nerve and are carried
of Corti
to the brain.
Scala tympani
The Organ of Corti
Travelling waves and the cochlear
The basilar membrane gets wider as it spirals from the
base at the oval window to the helicotrema at the apex.
The travelling waves build up to maximum amplitudes
at different places along the scala vestibuli, according
to their component frequencies: higher frequencies
closer to the base, lower frequencies closer to the
apex. In this way, different parts of the Organ of Corti
react to different frequencies, and different
strands of the auditory nerve receive and
transport frequency-differentiated impulses.
Travelling waves
Movement of the Organ of Corti
Central auditory
pathways
Frequency response in the cochlear nucleus
Neuronal response to a dynamic signal
Directional neurons