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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? 1 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 2 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 3 Three Domains of Sensory Research Sensory Physiology Physiological Psychology Psychophysics Physiological response Domain of Sensory physiology Physical stimulus Domain of sensory physiological psychology Sensory experience Domain of sensory psychophysics 4 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 5 Characteristics of Sound Least compression Frequency of a Greatest compression of molecules of molecules sound wave is related the pitch of a sound One cycle Amplitude Amplitude of a sound wave is (a) Higher frequency Lower frequency related to (Higher pitch) (Lower pitch) loudness of a Higher amplitude sound (Louder) Lower amplitude (Softer) (b) 6 Frequency of Sound Waves The frequency of a sound wave is measured as the number of cycles per second (Hertz) 20,000 4,186 1,000 100 27 Hz Hz Hz Hz Hz Highest Frequency we can hear Highest note on a piano Highest pitch of human voice Lowest pitch of human voice Lowest note on a piano 7 Intensity of Various Sounds Example Softest detectable sound P (in soundpressure units) Log P Decibels 1 0 0 10 1 20 100 2 40 1000 3 60 Loud music from a radio 10,000 4 80 Heavy automobile traffic 100,000 5 100 1,000,000 6 120 10,000,000 7 140 100,000,000 8 160 1,000,000,000 9 180 Soft whisper Quiet neighborhood Average conversation Very loud thunder Jet airplane taking off Loudest rock band on record Spacecraft launch 9from 150 ft.) 8 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 9 Anatomy of Ear Purpose of the structures in the ear: Measure the frequency (pitch) of sound waves Measure the amplitude (loudness) of sound waves 10 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 11 Anatomy of the Ear Pinna Semicircular Stirrup canals Hammer Anvil Bone Auditory nerve Sound waves Cochlea Auditory Canal- Eardrum (tympanic Membrane) Round window Oval window Where stirrup attaches 12 Anatomy of the Ear Outer ear Middle ear Inner ear Cochlea, partially uncoiled Tectorial membrane Hair cells Hammer Anvil Basilar membrane Stirrup Oval window Sound waves Auditory canal Eardrum Round window A sound causes the basilar membrane to wave up and down. 13 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 14 Coding of Sounds The pattern of vibration along the Basilar Membrane depends on the Frequency of the sound wave Oval window Direction of traveling wave Proximal end Distal end Basilar membrane 15 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 Vibration amplitude of basilar membrane Bassoon, loud Piccolo, soft Distance along basilar membrane (a) Effect of bassoon on basilar membrane Vibration amplitude of basilar membrane Piccolo, loud Bassoon, soft Distance along basilar membrane (b) Effect of piccolo on basilar membrane 16 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. 17 Auditory Masking Low frequency sounds effectively mask high frequency sounds High frequency sounds can not effectively mask low frequency sounds Vibration amplitude of basilar membrane Bassoon, loud Piccolo, soft Distance along basilar membrane (a) Effect of bassoon on basilar membrane Vibration amplitude of basilar membrane Piccolo, loud Bassoon, soft Distance along basilar membrane (b) Effect of piccolo on basilar membrane 18