Applied Psychoacoustics Lecture 1: Anatomy and Physiology of the human auditory system Jonas Braasch
Overview of the Human Ear
Outer Ear Pinna: External cartiledge –Provides direction dependent frequency cues for sound localization through spectral filtering –Position can be actively controlled by some mammals (e.g., cat) Meatus (Auditory Canal) –Pathway to the middle ear, approx. 7mm diameter, 27mm length –Amplifies sounds in the range of 2000 to 5000 Hz through resonance (approx. 10 – 15 dB)
Simulation of the sound pressure wave in the ear canal frontal, 2.7 kHz 2 lateral, 10 kHz 3 rear, 2.7 kHz
Photo of ear drum
Middle Ear
Middle Ear
Tympanic Membrane –Sound pressure vibration is trancduced into mechanical oscillation and passed on to the malleus –protects ear (e.g, water, wind) Ossicles –Malleus, incus, stapes (hammer, anvil, and stirrup) –are the Smallest bones in human body Muscles –Stapedius muscle (connected to the stapes) –Tensor tympani muscle (connected to the malleus) –are the smallest muscles in the human body Oval Window –connection to the cochlea Eustachian Tube –connects the middle ear to the throat for pressure relief
Function of the middle Ear Is an impedance transformer Without it difference in densities of air and the cochlear liquid would result in lossy energy transfer Pressure increase the pressure between the oval window and the ear drum by nearly a factor of 30 –Amplitude ratio ear (drum/stapes) ~1.3:1 –Area ratio (ear drum /oval window): ~20:1
Acoustic Reflex Transmission can be attenuated in the middle ear by stiffening the Stapedius muscle and the tensor tympani muscle to protect the inner ear Is controlled by the auditory system and react to loud sound exposure
Arrangement to measure the pressure-force transfer function of a middle ear (RUB-IKA)
Vibration of the ossicular chain
Inner Ear Semicircular canals Cochlear Auditory Nerve
Basilar Membrane
The Traveling Wave in the Basilar Membrane
Frequency Mapping on the BM Logarithmic Frequency Mapping
Traveling Wave Simulation Hz Tone 1000-Hz Tone 4000-Hz Tone
Neurotransmitters are chemicals that enable communication between two neurons are released from one neuron at its presynaptic nerve terminal and cross the synapse, a small gap, to the receptor of the second neuron
Connecting the ear to the auditory pathway 95% of auditory nerve fibres (Type-I fibres: large diameter, myelinated) innervate IHCs ( to a single IHC) sending information to the CNS 5% (Type-II fibres: thin, unmyelinated) innervate OHCs (each fibre innervating OHCs)
Tonotopic organization of auditory nerve and cochlear nucleus
Definition Tonotopy (from greek tono- and topos = place: the place of tones) is the spatial arrangement of where sound is perceived, transmitted, or received. It refers to the fact that tones close to each other in terms of frequency are represented in topologically neighbouring neurons in the brain. from Wikipedia
Cell Response Types Primary-like (PL) Primary-like, notch (PL-N) Phase-lock (onset) Onset, lock (O-L) Chopper
Cell types time Acoustic stimulus Primary-like chopper onsetPrimary-like, notch
Tuning Curves
Post Stimulus Time (PST) Histogram
Phase Locking sound pressure action potential
Physiological Coordinate System DirectionDescription LateralAway from the midline MedialToward the midline BilateralOn both sides of the body or head IpsilateralOn the same side of the body or head ContralateralOn the opposite side of the body or head