Sound Localization

1
Sound Localization
2
Sound Localization (cont.)

• Binaural Neurons (A1) compare information
  differences from the two ears
• Interaural Time - Slight delay in the arrival of
  a signal to the further ear (0 - 7/10,000 sec.)

3
Sound Localization (cont.)

• Interaural Intensity - Slight differences in
  loudness to each ear - the head occludes some
  sound
• Phase Disparity - The peaks (compressions) and
  valleys of the sound waves arrive at different
  times for the two ears - good for continuous
  sound sources - Barn owls use this to catch
  running mice in total darkness

4
Sound Localization (cont.)
5
Cone of Confusion

• Using normal cues, all you can detect is the time
  difference between your two ears. This specifies
  an azimuth not a position.

6
Cone of Confusion
Solution - tilt your head, like the RCA dog
7
Auditory Scene Analysis
8
Auditory Scene Analysis

• Separation of sounds into distinct streams -
  how is it that complex sounds are grouped
  appropriately?
• Common Time Course or Sequential Integration -
  sounds are grouped together according to which
  ones vary together over time - eventually
  distinct sources of sound will produce distinct
  sounds
• Sound Location or Simultaneous Integration -
  sounds which emanate from the same source

9
Auditory Scene Analysis (cont.)

• Spectral Harmonics - Harmonic frequencies are
  multiples of the fundamental frequency
• Familiar sounds - groups of sound which have
  been perceived as together in the past are more
  easily grouped together in the present
• Visual (or other perceptual) input can help to
  sort out which sounds belong with which source

10
Auditory Scene Analysis (cont.)

• How do listeners know how far a sound is?
• Simplest cue Relative intensity of sound
• Inverse-square law As distance from a source
  increases, intensity decreases faster such that
  decrease in intensity is distance squared
• Spectral composition of sounds Higher
  frequencies decrease in energy more than lower
  frequencies as sound waves travel from source to
  one ear
• Relative amounts of direct vs. reverberant energy

11
Auditory Scene Analysis (cont.)
12
Auditory Event Perception

• Quantity
• Length
• Volume
• Energy
• Velocity
• Time Course

13
Attention

• Once target sounds are determined and segmented,
  the brain amplifies those and diminishes others -
  The Cocktail Party Effect