Chapter 9 Majority of illustra3ons in this presenta3on are from Biological Psychology 4 th edi3on ( Sinuer Publica3ons) Sound Waves Sound waves are composed of compression and rarefac3on of air molecules. Vibra3ng membrane (water here) like that of a drum causing air molecules to compress and rarefy www.webbofscience.com 2 Sound and Sensa3on Physical Domain Psychological Frequency Intensity Quality Pitch Loudness Timbre 3 1
Frequency and Pitch Frequency is defined as vibra3on in number of cycles per second measured in hertz (Hz). Pitch is our percep3on of frequency. 4 Intensity and Loudness Intensity is the amount of energy (measured in decibels, db) in a wave, represented or determined by its amplitude. This relates to perceived loudness. 5 Example of Loudness Loud Thunder (120 db) outdoor- lightszone.com Normal Conversa3on (60 db) www.psychologytoday.com 6 2
Quality and Timbre Quality of sound is based on fundamental frequencies. We recognize the differences in the sound of a zither from a guitar due to 3mbre. Zither www.fretlesszithers.com Guitar www.1chris3an.net 7 Fundamental Frequencies A one fundamental frequency (F1) like a pure tone produced by a tuning fork is a simple sound. However most sounds are complex and have many fundamental frequencies (F1, F3, F5 etc) e.g., piano. www.pushpullbar.com 8 Fourier Transforma3on 1. A mathema3cal way of decomposing complex wave pa`erns into simple waves is called Fourier Transforma3on. 2. The pa`ern decomposes into fundamentals or harmonics (overtones), making it possible for us to dis3nguish among musical instruments or other sounds. www.schoolphysics.co.uk 9 3
The External Ear The ear has three divisions or parts: external, middle, and inner ear. External ear or pinna collects sounds and filters sound frequencies. 10 The Middle Ear Consists of a chamber between eardrum and cochlea containing three 3ny bones (malleus, incus, stapes) that transfer vibra3ons of the eardrum on to the cochlea s oval window. 11 The Inner Ear Inner ear contains the cochlea. A snail shaped organ with two large fluid- filled canals (ves3bular and tympanic) and a small canal (middle). The ves3bulocochlear nerve (VIII) leaves cochlea. 12 4
The Unwound Cochlea Unwound cochlea is broad at the base and tapers at the apex. The basilar membrane is narrow at the base, but broadens at the apex. 33 mm 0.1 mm Base Apex 0.5 mm Cochlea Basilar Membrane 13 The Basilar Membrane Basilar membrane separates tympanic and middle canals. The organ of Cor3 sits on top of this membrane and contains two sets of hair cells that carry auditory messages to the brain. hyperphysics.phy- astr.gsu.edu 14 Hair Cells and Transduc3on Inner and outer hair cells have afferent and efferent pathways. Mechanical pressure on these hair cells results in acous3cal transduc3on, conver3ng mechanical energy into neural energy. 15 5
Hair Cells Inner Hair Cells There are 3500 inner hair cells (IHC) in the cochlea IHC connect to 16-20 auditory nerve fibers About 90-95% of these fibers carry auditory messages to the brain Outer Hair Cells There are 12,000 outer hair cells (OHC) in the cochlea OHC can change their length to s3ffen the basilar membrane. OHC are involved with cochlear amplifica3on Electron micrograph of hair cells 16 Tip Links Stereocilia open channels through 3p links in IHC that let K + enter the cell. This depolarizes the cell, Ca 2+ enters the cell to release neurotransmi`er glutamate. 17 Auditory Pathway Primary Auditory Cortex MGN MGN Primary Auditory Cortex Inferior Colliculus Inferior Colliculus Superior Olivary Nucleus Superior Olivary Nucleus Cochlear Nucleus Cochlear Nucleus Cochlea Cochlea 18 6
19 Place Theory Chiefly Helmholtz and later von Békésy suggested that sound frequencies s3mulate basilar membrane at specific places resul3ng in perceived pitch. Summarized some3mes as pitch is which. Helmholtz (1821-1894) Von Békésy (1899-1972) 20 Place Theory Békésy showed that different frequencies from high to low registered on the basilar membrane extending from the base (cochlear window) to the apex of the cochlea. 21 7
Temporal Theory 1. Place theory works well to explain frequencies up to 1600Hz, but humans can hear frequencies close to 20,000Hz. 2. To explain that Weaver proposed the temporal theory. He suggested that the rate of nerve impulses matched the frequency of a sound. Glen Weaver (1902-1991) 22 Temporal Theory 3. Weaver used the volley principle of firing rounds of bullets to explain how neurons fire volleys of impulses to sense high frequency sounds. Sound Frequency Nerve impulse 1000 Hz 2000 Hz 23 Localiza3on of Sound 1. When sound reaches one ear faster (latency differences) than the other makes us localize the sound in space. 2. Sounds that reach one ear louder than the other (intensity differences) also result in its localiza3on. 24 8
Throwing Sound: Illusion Ventriloquists use the illusion of throwing sound from the mouth piece of a prop which moves. Clyde, Kevin Johnson & Ma3lda 25 Hearing Prosthe3cs Prosthe3cs to replace cochlea in the inner ear. 26 9