Post on 01-Apr-2015
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Sensation and Perception
In this part of the course we will try to answer such questions as: How do we see and hear? Why does a TV only need three
phosphors (Red, Green and Blue) to allow us to see all colors?
Why are some sounds easier to hear than others?
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Sensation
Sensation - the registration of physical stimuli Hearing - anatomy and function of the
ear Vision - anatomy and function of the eye Psychophysics - the measurement of
sensory experiences
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Sensation
What is the purpose of sensory processing? To transform physical stimuli in the
environment into neural signals in the brain
Example (Hearing): Sound waves are transformed into vibrations in the ear, and the strength of those vibrations are coded by sensory neurons
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Three Domains of Sensory Research
Sensory PhysiologyPhysiological PsychologyPsychophysics
Sensory experiencePhysical stimulus
Domain of Sensory physiology
Domain of sensory psychophysics
Domain of sensoryphysiological psychology
Physiological response
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Hearing: Sound Waves
Auditory perception occurs when sound waves interact with the structures of the ear.
Sound Wave - changes over time in the pressure of an elastic medium (for example, air or water).
Without air (or another elastic medium) there can be no sound waves, and thus no sound
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Characteristics of Sound
Frequency of a sound wave is related the pitch of a sound
Amplitude of a sound wave is related to loudness of a sound
Greatest compressionof molecules
Least compressionof molecules
One cycleAmplitude
Higheramplitude(Louder)
Loweramplitude(Softer)
Higher frequency(Higher pitch)
Lower frequency(Lower pitch)
(a)
(b)
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Frequency of Sound Waves
The frequency of a sound wave is measured as the number of cycles per second (Hertz) 20,000 Hz Highest Frequency we can hear 4,186 Hz Highest note on a piano 1,000 Hz Highest pitch of human voice 100 Hz Lowest pitch of human voice 27 Hz Lowest note on a piano
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Intensity of Various Sounds
ExampleP (in sound-pressure units) Log P Decibels
Softest detectable sound
Soft whisper
Quiet neighborhood
Average conversation
Loud music from a radio
Heavy automobile traffic
Very loud thunder
Jet airplane taking off
Loudest rock band on record
Spacecraft launch 9from 150 ft.)
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10
100
1000
10,000
100,000
1,000,000
10,000,000
100,000,000
1,000,000,000
0
1
2
3
4
5
6
7
8
9
0
20
40
60
80
100
120
140
160
180
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Intensity of Sound Waves
The physical intensity of sound waves is measured on the decibel (dB) scale Intensity (in dB) = 20 log (P/P0) P = intensity of sound being measured P0 = the lowest intensity 1,000 Hz tone we
can hear
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Anatomy of Ear
Purpose of the structures in the ear: Measure the frequency (pitch) of
sound waves Measure the amplitude (loudness)
of sound waves
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Major Structures of the Ear
Outer Ear - acts as a funnel to direct sound waves towards inner structures
Middle Ear - consists of three small bones (or ossicles) that amplify the sound
Inner Ear - contains the structures that actually transduce sound into neural response
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Anatomy of the Ear
Pinna
Soundwaves
AuditoryCanal-
Stirrup
Cochlea
Auditorynerve
Semicircularcanals
Roundwindow
Oval windowWhere stirrupattaches
Eardrum(tympanicMembrane)
Bone
Hammer
Anvil
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Anatomy of the Ear
Outer ear Middle ear Inner ear
A sound causesthe basilarmembrane to waveup and down.
Basilarmembrane
Hair cells
Tectorialmembrane
Round window
Eardrum
Oval window
Cochlea,partiallyuncoiled
Stirrup
AnvilHammer
Soundwaves
Auditorycanal
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Transduction of Sounds
The structures of the ear transform changes in air pressure (sound waves) into vibrations of the Basilar Membrane.
As the Basilar Membrane vibrates it causes the hairs in the Hair Cells to bend.
The bending of the hairs leads to a change in the electrical potential within the cell
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Coding of Sounds
The pattern of vibration along the Basilar Membrane depends on the Frequency of the sound wave
Basilarmembrane
Distalend
Proximalend
Oval window
Direction of traveling wave
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Coding Sounds
Low frequency sounds cause more vibration near distal of Basilar Membrane
High frequency sounds cause more vibration near proximal end of Basilar Membrane
Piccolo, soft
Bassoon, loud
Piccolo, loud
Bassoon, soft
Distance along basilar membrane
(a)
Distance along basilar membrane
(b)
Effect of bassoon on basilar membrane
Vibration amplitude of basilar
membrane
Vibration amplitude of basilar
membrane
Effect of piccolo on basilar membrane
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Coding and Auditory Masking
The way in which waves travel down the Basilar Membrane causes some sounds to interfere with (or mask) our ability to hear other sounds
Low frequency sounds provide better masking than high frequency sounds.
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Auditory Masking
Low frequency sounds effectively mask high frequency sounds
High frequency sounds can not effectively mask low frequency sounds
Piccolo, soft
Bassoon, loud
Piccolo, loud
Bassoon, soft
Distance along basilar membrane
(a)
Distance along basilar membrane
(b)
Effect of bassoon on basilar membrane
Vibration amplitude of basilar
membrane
Vibration amplitude of basilar
membrane
Effect of piccolo on basilar membrane