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AUDITORY PERCEPTION
• Pitch Perception
• Localization
• Auditory Scene Analysis
Pitch Perception
• Pitch is mostly determined by sound
frequency
• Intensity also influences pitch:
– For high frequency sounds, pitch increases with
intensity
– For low frequency sounds, pitch decreases with
intensity
Frequency Theory
• Pitch is perceived based on the frequency of
action potentials
• Problem: we can perceive frequencies up to
20,000 Hz, but neurons can respond no more
than 1000 times per second
• phase locking (volley principle): groups of
neurons could work together
Place Theory
• Pitch is perceived based on which portion of
the basilar membrane is stimulated
• The traveling wave peak is fairly precise
because of modulation with outer hair cells
(motile response)
Which Theory is Right?
•
•
•
•
Both!
Frequency up to about 500 Hz
Frequency and Place for 500-4000 Hz
Place for high frequencies
Frequency Processing in the Primary
Auditory Cortex (A1)
• Tonotopic organization
• All neurons in a column have the same
characteristic frequency
• Phase locking up to 500 Hz
Locating Sound Sources
• Azimuth - left/right location
• Elevation - vertical location
• Distance
Azimuth
• Interaural Level Differences
– sound is more intense in one ear
– head serves as acoustic shadow
– large differences for sounds up to 1000 Hz
• Interaural Time Differences
Elevation
• Spectral Cues - effects of head and pinnae on
sounds (Head Related Transfer Function)
Distance Information
• Sound level (for familiar sounds)
• Frequency - more distant sounds lose high
frequencies
Distance Information
• Motion Parallax - closer sounds shift location
more quickly than more distant sounds
• Indirect Sound - amount of reflected sound
increases with distance
Localization: Auditory Cortex
• ITD detectors respond to specific time of
arrival differences
• Large receptive fields
• Panoramic neurons have different firing
patterns for different directions
Auditory Scene Analysis
• Auditory Scene - array of all the sounds in
the environment
• How are these sounds grouped and
separated into coherent perceptions?
• auditory stream segregation - sounds
entering the ear are grouped into
perceptual streams
Auditory Scene Analysis
• pitch grouping - similar pitches will be
recognized as part of the same pattern
– scale illusion : present ascending and descending
scales simultaneously, alternating notes between
ears; the high notes are heard in one ear and the
low notes are heard in the other ear
Auditory Scene Analysis
• location grouping - sounds coming from the
same location are grouped
• timbre grouping - sounds with same timbre
are grouped
• loudness grouping - sounds of similar
loudness are grouped into the same
pattern
Auditory Scene Analysis
• onset and offset - group sounds that start
and stop at the same time
• good continuation - group sounds that are
constant or that change smoothly
• experience - a melody schema may help in
recognizing a melody