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Lecture 9

Lecture 9.odt

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University of Toronto St. George
Matthias Niemeier

1 Lecture 9 – Hearing (Chapters 9 & 10) ➢ Explain premotor theory of attention ➢ Attention precedes eye movememnt ➢ Overt attention: eye movement; it's obvious ➢ Covert attention: you dont need to move your eyes, occulomotor program is not activated. ➢ There's a close connection btwn shifts of attention and eye movememnts. Chapter 9 ➢ The Basics:  Nature of sound  What is sound? • Sound is created when an object vibrates • Vibrations of object: cause molecules in object's surrounding medium to vibrate as well which causes pressure changes in medium • Longitudinal sound wave • Speed of sound depends on density of medium • -Air: 340 m/s • -Water: 1500 m/s • Amplitude: Sound wave can be small or pronounced (Sound is louder or faint) – the height of the wave/magnitude • Frequency: • Intensity: Physical measure of how loud something is. Expressed in decibels sound pressure level (dB SPL). • Amount of sound energy falling on a unit area • Decibels: Ratio btwn the pressure of some sound and the pressure of a reference sound p0 (minimum) • 6 decibels = twice as loud as something else • 12 decibels = twice as loud as 6 decibels • It increases by doubling • So this is all intensity • Intensity is related but not equal to loudness • Loudness: The psychological aspect of sound related to perceived intensity or magnitude • Humans can hear across a wide range of sound intensities • Ratio btwn faintest and loudest sounds is more than one to one million, 6dB= double amount of pressure. • Frequency: For sound, the number of times per second that a pattern of pressure change repeats • Measured in 1/s = Hz • 10 Hz = 10 beats per second • Is associated with pitch • Pitch: Psychological aspect of sound related to the fundamental frequency (low: tuba, high: piccolo). • Relationship btwn frequencies and intensity. 2 • Very very low frequencies cannot be heard • We're much better at hearing higher frequencies (the thresholds are the lowest) •  One of the simplest kinds of sounds: Sine wave, or pure tone • Since wave: waveform for which variation as a function of time is a sine function • Most sounds in world: Complex sounds (compositions of individual sine waves: human voices, birds, cars, etc) • All sound waves can be described as some combination sine waves • Complex sounds can be described by Fourier analysis • Spectrum: Arepresentation of the relative energy present at each frequency • The frequencies increase as multiples • Harmonic Spectrum: Typically caused by simple vibrating source (string of a guitar). The frequencies of its components are integer multiples of lowest frequencyst • Fundamental frequency: Lowest frequcny component of a sound (= 1 harmonic) • Sounds with same pitch and loudness may still sound same (piano vs. Guitar) = timbre. • Why? We perceive the pitch of the two sounds to be equal to the first fundamental frequency. But in fact there are way more frequencies to the complex sound than the first one. Pitch and frequency is not the same.  Anatomy and physiology of the auditory system  Outer Ear • Pinna • collects sounds from the environment • funnels sound waves into ear canal • Ear Canal • Shape and length enhance sound frequencies • Main purpose is to insulate structure(Tympanic Membrane) at its end • Both pinna and ear canal protect the rest of the ear from damage • Tympanic Membrane • Vibrates in response to sound • Outer ear ends with the last piece = tympanic membrane • it is hit by sound pressure waves\ • if it is damaged, you can't hear • sometimes it can heal itself, but there might be a scar left = can't hear higher frequencies •  Middle Ear • 3 tiny bones (ossicles) = smallest bones in the body • Malleus • Directly sits on the Tympanic Membrane, next comes Incus, and Stapes • Incus • Stapes • These bones pick up vibrations of the membrane and transfer it to the oval window( in the inner ear – smaller than membrane) = convergence = so your transfering from a wide area to a small area = amplifies sound. • Ossicles are also connected to muscles which is also associated with amplification (loudness can be reduced due to contraction of muscles) •  Inner Ear 3 • Cochlea • snail-structure, includes auditory organ • consists of a round and oval window (exit and entrance of sound pressure) • 3 canals • Middle Canal • Vestibular Canal /Tympanic Canal • These canals are seperated by membranes • One top of one of the membranes we have the organ of corti. • Organ of corti transforms sound pressure waves into neuro-signals • This experiences motion and that is how the neurons in the inner air are stimulated • 3 components • inner hair cells
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