Sensation and Perception

1. 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?

2. 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

3. 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

4. Physiological response Domain of sensory physiological psychology Domain of Sensory physiology Physical stimulus Sensory experience Domain of sensory psychophysics Three Domains of Sensory Research • Sensory Physiology • Physiological Psychology • Psychophysics

5. 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

6. Least compression of molecules Greatest compression of molecules One cycle Amplitude (a) Higher frequency (Higher pitch) Lower frequency (Lower pitch) Higher amplitude (Louder) Lower amplitude (Softer) (b) 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

7. 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

8. Intensity of Various Sounds P (in sound- pressure units) Example 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.) 0 1 2 3 4 5 6 7 8 9 0 20 40 60 80 100 120 140 160 180 1 10 100 1000 10,000 100,000 1,000,000 10,000,000 100,000,000 1,000,000,000

9. 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

10. Anatomy of Ear • Purpose of the structures in the ear: • Measure the frequency (pitch) of sound waves • Measure the amplitude (loudness) of sound waves

11. 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

12. Semicircular canals Pinna Stirrup Hammer Bone Anvil Auditory nerve Sound waves Cochlea Eardrum (tympanic Membrane) Auditory Canal- Round window Oval window Where stirrup attaches Anatomy of the Ear

13. Outer ear Middle ear Inner ear Cochlea, partially uncoiled Tectorial membrane Hair cells Hammer Anvil Basilar membrane Stirrup Oval window Sound waves Auditory canal A sound causes the basilar membrane to wave up and down. Eardrum Round window Anatomy of the Ear

14. 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

15. Oval window Direction of traveling wave Proximal end Distal end Basilar membrane Coding of Sounds The pattern of vibration along the Basilar Membrane depends on the Frequency of the sound wave

16. 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 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

17. 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.

18. 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 Auditory Masking • Low frequency sounds effectively mask high frequency sounds • High frequency sounds can not effectively mask low frequency sounds