Speech Science XI

Speech Perception

(auditory physiology)

Version WS 2007-8

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

• 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.

Outer Ear

Eardrum

•

Middle Ear 1

Here we see the positionof the three bones whichstrengthen the mechanical signal produced by theeardrum and transfer it tothe inner ear via the ovalwindow.The malleus (hammer) isattached to the eardrumby the manubrium (handle)and vibrates with it. Thevibrations are passed on to the incus (anvil) andfrom there to the stapes

(stirrup). The „footplate“of the stiirup is attachedto the „oval window“, amembrane separating themiddle ear from the innerear.

Middle Ear

Malleus

Incus

Stapes

The bones in the human ear are the smallest bonesin the body:

The hammer: (Malleus)5.5 mm

The anvil: (Incus)5 mm

The footplateof the stirrup: (Stapes)3.2 x 1.4 mm

Middle Ear 2

Middle ear amplification

Inner EarThe inner ear has twofunctional components:The vestibular systemfor balance (the semi-circular canals) and theauditory system (thecochlear).The cochlear is dividedlengthways by two mem-branes into three sections:The scala vestibuli, scalamedia and scala tympani.The membrane of the ovalwindow vibrates with thestapes and send waves down the s.vestibuli. Atthe end of the s.vestibuli,they pass into the s. tympanivia the helicotrema, and are damped by the roundwindow

oval window

round window

Scala mediaScala mediaScala mediaScala vestibuli

Scala tympani

helicotrema

Inner Ear 2

Above: Section through the cochlear showingthe three scalae. Below: a magnified cross sectionat one point in the cochlear.

Scala mediaScala vestibuli

Scala tympani

Scala tympani

S. media

Scala vestibuliBasilar

membranewith Organof Corti

Reissner‘s membrane

Travelling waves in the scalavestibuli make the Reissner‘smembrane vibrate, transferringvibrations to the Organ of Cortion the Basilar membrane.The Organ of Corti has finehair cells which, when disturbedby the vibrations, produce smallelectrical discharges. This is the stage at which theoriginally acoustic signal enters the nerve system.The electrical discharges from the hair cells transfer to theauditory nerve and are carriedto the brain.

The Organ of Corti

Travelling waves and the cochlear

The basilar membrane gets wider as it spirals from thebase at the oval window to the helicotrema at the apex.The travelling waves build up to maximum amplitudesat different places along the scala vestibuli, accordingto their component frequencies: higher frequencies closer to the base, lower frequencies closer to theapex. 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 auditorypathways

Frequency response in the cochlear nucleus

Neuronal response to a dynamic signal

Directional neurons