Speech Science XI Speech Perception (auditory physiology) Version WS

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., pp (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 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 Incus Stapes 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 Middle Ear 2

Middle ear amplification

Inner Ear The inner ear has two functional components: The vestibular system for balance (the semi- circular canals) and the auditory system (the cochlear). The cochlear is divided lengthways by two mem- branes into three sections: The scala vestibuli, scala media and scala tympani. 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 oval window round window Scala media Scala vestibuli Scala tympani helicotrema

Inner Ear 2 Above: Section through the cochlear showing the three scalae. Below: a magnified cross section at one point in the cochlear. Scala media Scala vestibuli Scala tympani S. media Scala vestibuli Basilar membrane with Organ of Corti Reissner‘s membrane 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 hair cells which, when disturbed by the vibrations, produce small electrical discharges. This is the stage at which the originally acoustic signal enters the nerve system. The electrical discharges from the hair cells transfer to the auditory nerve and are carried to the brain.

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