Psyc 102

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Psyc 102

• HEARING

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If a tree crashes to the ground in an uninhabited
forest, does it make a sound?

• Physics Yes, mechanical waves
• Psychology No, no resulting sensation in a brain

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Stimulus Sensation(physics)
(psychology)

• Amplitude Loudness
• Intensity
• Frequency (x2) Pitch (1 octave)
• Phase (of 2 waves) Stereo direction

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Hearing threshold

• Faintest sound you can just hear
• Low threshold high (good) sensitivity
• Threshold is lowest at 1--5 KHz

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• Audiogram (Hearing curve)

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Evolution of Hearing from the Lateral Line System
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The frog as a resonator
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Next

• Anatomy -- more details
• Deafness
• Sound localization
• Selective listening

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Cochlear hair cells

• Inner hair cells
• 25 of total hair cells
• 95 of input to brain

Outer hair cells 75 of total hair cells Only 5
of input to brain Receive descending
fibers Probably little motors to stiffen basilar
membrane
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• A 2-hour exposure to loud noisesimilar to a loud
  rock bandhas seriously damaged the hair cells of
  a cat's inner ear. All the tall cilia on the
  right of this picture have disappeared or fused
  together and fallen over.

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• When this bundle of 50 to 60 cilia at the top of
  a hair cell vibrates in response to sound, the
  hair cell (from a bullfrog's inner ear) produces
  an electrical signal. Tiny tip links can be seen
  joining the tops of shorter cilia to the sides of
  taller ones (arrow).

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Hearing and Deafness
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• Clinical audiogram (Hearing loss)
• Normal hearing horizontal line at top 0 dB
  hearing loss
• (Up is good)

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Causes of deafness

• Disease (rare)
• Noise
• Age (related to noise exposure?)

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Causes of deafness1. Menieres Disease

• Fluid in the inner ear.
• Vertigo (dizziness)
• Tinnitus (ringing in the ear)

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Causes of deafness2. Noise

• Temporary threshold shift
• Boilermakers disease
• Artillery officers
• Eustachian tube
• Rock music?
• Dentists Tonal dip

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Causes of deafness3. Age

• Presbyacusia high frequency loss (gt5KHz)
• Caused by cumulative exposure to noise?
• Mabaan tribesmen in Ethiopia
• 85 year old in Amsterdam previously blocked ear
  like 30 year olds

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Two kinds of deafness Conduction
deafnessNerve deafness
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Conduction deafness

• Eardrum becomes slack with age
• Perforated eardrum
• Broken ossicle can be replaced surgically

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Nerve deafness

• Destruction of cochlear hair cells
• Acoustic neuroma
• Difficult to treat
• Use a hearing aid

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Sound localization
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• Sound localization
• Intensity difference (sound shadow) Best for
  high frequencies
• Time difference Best for low frqeuencies

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Relative intensity(Sound shadow of head)

• Sound frequency
• 100 Hz
• 1000 Hz
• 10,000 Hz

• Intensity difference (dB)
• 0
• 30
• 80

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Relative delay(Time difference at 2 ears)

• Direction
• 0 (ahead)
• 2
• 30
• 90 (max)

• Delay
• 0 msec
• 40 microsec
• 270 microsec
• 680 microsec

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• Gloved Dr. Dan Feldman in Knudsens lab at
  Stanford prepares an owl for a hearing
  experiment.

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• After wearing prism spectacles a few months, this
  owl began to miss auditory targets as the sound
  localization system in its brain tried to
  harmonize with the visual system, which received
  erroneous cues.

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• 5 meter sphere at Wright Patterson Air Force
  Base in Dayton, Ohio. 277 loudspeakers. 6 meter
  cubical anechoic chamber Listeners in
  localization experiments indicate perceived
  source directions by placing an electromagnetic
  stylus on a small globe. (Mark Ericson and
  Richard McKinley.)

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• Anechoic chamber

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Sound localization by Ormia, an acoustic
parasitic fly

• Phonotaxis like you wouldnt believe
• Slides from Dr. Roberts, University of Toronto

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Attention selective listening

• Can you attend to two things at once?
• The cocktail party problem How are we able to
  attend selectively to one voice out of many who
  are speaking?

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Questions in selective listening

• How can we attend to only one voice (the cocktail
  party problem)?
• Ans We use cues of pitch/timbre direction.
• Can we attend to two voices at once?
• Ans Mostly not.

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Shadowing occupies attention
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Selective attention how much of the weather
forecast will he hear while shadowing the woman?
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Meaning CAN guide selective listeningLeft ear
Once upon a.....papers today?Right ear Have
you read.....time there was a king.
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Changes in unattended (unshadowed) message which
are

• HEARD
• Male changes to female voice
• Voice changes to music

• NOT HEARD
• English changes to French

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Threshold for hearing your OWN NAME is lower than
for other sounds