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Chapter 11

Chapter 11. Sound, Audition, and Pitch. Ability to Hear. When given the choice between hearing and seeing, most people would choose to go without sight to retain hearing Communication and music Helen Keller, who is both deaf and blind has said that being deaf is worse

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Chapter 11

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  1. Chapter 11 Sound, Audition, and Pitch

  2. Ability to Hear • When given the choice between hearing and seeing, most people would choose to go without sight to retain hearing • Communication and music • Helen Keller, who is both deaf and blind has said that being deaf is worse • Blindness isolates you from “things” • Deafness isolates you from “people”

  3. Pressure Wavesvs. Perceptual Experience • The word “sound” is used in two different ways • Physical definition: Pressure changes in the air or other medium • Perceptual definition: Experience we have when we hear

  4. Pressure Wavesvs. Perceptual Experience • Sound waves • Pattern of air pressure changes, which travel through the air at 340 meters per second (travel through water @ 1500 meters per second) • This is analogous to ripples created by a pebble dropped into a pool of water • The water at a particular place moves up and down (not moving outward) • Hearing • The perceptual result of the air pressure changes

  5. Amplitude and Loudness • Amplitude • The size of the pressure change • Height of a sine wave • Frequency • Number of cycles per second • Or the number of times the pressure changes repeat

  6. Amplitude and Loudness • Larger amplitudes are associated with an increase in the perceptual experience of Loudness

  7. Amplitude and Loudness • Decibel • A compressed unit of sound created by Alexander Graham Bell • Decibels, which are a physical measure, are related to the psychological experience of loudness.

  8. Frequency and Pitch • Frequency is indicated in Hertz (Hz) • 1 Hertz is 1 cycle per second • Frequency is linked to the experience of pitch • This is the quality of the tone that we describe as being “high” or “low”

  9. The Range of Hearing • We only hear within a specific range of frequencies • Humans = 20 Hz – 20,000Hz • Audibility Curve • How sensitivity to sound changes across the range of hearing • Threshold is lowest for 2,000 Hz - 4,000 Hz (range of human speech)

  10. The Range of Hearing

  11. Timbre • A sound can have the same loudness, pitch, and duration, but still sound different • This difference is a difference in timbre • Same note on a flute vs. bassoon • So far we’ve been talking about pure tones • One frequency in the sound • Our auditory experience is more dominated by complex sounds. The complex stimuli can contain many frequencies • Additional frequencies create different timbres

  12. Timbre • Additive synthesis • Can be used to produce complex sounds by adding simple components • Starting point = fundamental frequency (or 1st harmonic) • Then add additional pure tones (at double the frequency; 440Hz, 880Hz, 1320Hz) • The additional tones are higher harmonics of the tone

  13. The ear

  14. External Ear • External Ear (Pinna) collects sound • Pinna modifies the sound in “hills & valleys” • Shape of ear increases reception of sound 2000-5000 Hz (human speech) • Also important for sound localization • Sound waves next travel down the ear canal

  15. Middle Ear • Ossicles • Located at the end of the ear canal • 3 Tiny bones • Malleus • Incus • Stapes • Connects the tympanic membrane to the oval window (part of inner ear)

  16. Middle Ear • Small movements of the tympanic membrane moves the ossicles, which then move the oval window • This “set up” amplifies sound pressure so that it will move the fluid in the inner ear

  17. Middle Ear • Two muscles (tensor tympani & stapedius muscles) are activated to protect the inner ear from damaging sounds by stopping very large movements of the ossicles. • Called the “Stapedius muscle reflex”. • These muscles are activated by “self-made” sounds (e.g., speaking, chewing, etc.) so they are not too loud • The muscles tense before any “self-made” sound is made.

  18. Inner Ear: Cochlea • When movement of the oval window moves the fluid in the cochlea it then pushes on the round window • Round window separates the Tympanic canal from the middle ear.

  19. Inner Ear: Cochlea • Cochlea has 3 canals • Vestibular canal • Middle canal • Tympanic canal

  20. Inner Ear:Cochlea (Organ of Corti) • Principal components that convert sounds into neural activity • Three structures: • Hair Cells • Framework of supporting cells • Termination of auditory fibers

  21. Inner Ear:Cochlea (Organ of Corti) • Unrolled Cochlea • Base of Cochlea = basilar membrane • Varying amounts of pressure on the fluid (via the stapes) causes oscillating movement in the basilar membrane. • Sensitive to different frequencies of sound • High frequencies--> near base • Low frequencies--> near apex

  22. Inner Ear:Cochlea (Hair Cells) • Inner Hair Cells (IHC) • 1 row (3500 cells) • Flask-shaped • Outer Hair Cells (OHC) • 3 rows (12,000 cells) • Cylindrical

  23. Inner Ear:Cochlea (Hair Cells) • 50 - 200 Small hairs protrude from top of each hair cell. • Hairs = stereocilia • Hairs progressively increase in height across hair cell

  24. Inner Ear:Cochlea (Hair Cells) • Stereocilia of OHCs protrude into the indentations of the bottom of the tectorial membrane

  25. Inner Ear:Cochlea (Hair Cells) • Nerve fibers contact the bottom of the hair cells • 4 Kinds of synapses & nerve fibers • (1&3) afferents; send info from hair cells to brain • (2&4) efferents; send messages from brain to hair cells

  26. Inner Ear:Cochlea (Hair Cells) • IHCs • Each is associated with 16-20 nerve fibers • Afferent fibers from IHCs account for 90-95% of all afferent nerve fibers from this area • Responsible for perception of sound

  27. Inner Ear:Cochlea (Hair Cells) • OHCs • Few nerve fibers connect to each OHC • Function of OHC: modulating acoustic stimulation • Efferent inputs from CNS instruct stereocilia to lengthen or shorten • Influences mechanics of sound by stiffening or relaxing portions of the basilar membrane

  28. Inner Ear:Cochlea (Hair Cells) • OHCs • Efferent inputs from CNS also inhibits inputs from very loud sounds

  29. Inner Ear:Cochlea (Sound Production) • After middle and inner ear activity, sounds induce vibrations in the basilar membrane • Vibrations bend the stereocilia inserted into the tectorial membrane • Stereocilia turn vibrations into neural signals

  30. Inner Ear:Cochlea (Sound Production) • Vibrations bend the stereocilia and open ion channels via tip links • Thread-like fibers (tip links) run along the top of the stereocilia • Tip links increase tension & ion channels open like trap doors • Happens in fractions of a millisecond

  31. Inner Ear:Cochlea (Sound Production) • Displacement of stereocilia opens K+ channels; depolarizes cell • Ca2+ enters cell which causes vesicles to release neurotransmitters • Neurotransmitters bind to afferent fibers at base of hair cells

  32. Inner Ear:Cochlea (Sound Production) • IHCs use glutamate as neurotransmitter • OHCs use acetylcholine and GABA as neurotransmitter

  33. Inner ear --> Brain • Auditory fibers from cochlea make up the vesibulocochlear (VIII) cranial nerve • Majority of these fibers are from IHCs

  34. Inner ear --> Brain • Auditory nerve --> dorsal & ventral cochlear nuclei • Cochlear nuclei --> Superior olivary nucleus • Superior olivary nucleus receives input from both left and right cochlear nuclei • First stage of binaural (two-ear) information for sound localization

  35. Inner ear --> Brain • Superior olivary nucleus --> Inferior colliculus • Inferior colliculus --> Medial geniculate nucleus (thalamus) • At least two different paths from MGN to auditory cortex

  36. Inner ear --> Brain • Cochlea to auditory cortex • Tonotopic organization • Auditory neurons are spatially arranged in an orderly map according to the frequencies to which they respond.

  37. Inner ear --> Brain • Tonotopic maps in different mammal species • Arrows go from low to high frequencies • A1 = primary auditory cortex

  38. Within the auditory cortex • Core • Primary auditory area (A1) + some surrounding areas • Activated by simple sounds • Belt  Parabelt • Requires complex sounds for activation

  39. Specialization • Different areas of auditory cortex are specialized for different activities • Localization • Movement of sounds • Perception of species-specific sounds • Etc. • In humans, fMRI studies show that some areas even “light up” when people try to lip read.

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