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AUDITORY PERCEPTION

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

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AUDITORY PERCEPTION

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  1. AUDITORY PERCEPTION • Pitch Perception • Localization • Auditory Scene Analysis

  2. 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

  3. 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

  4. 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)

  5. Which Theory is Right? • Both! • Frequency up to about 500 Hz • Frequency and Place for 500-4000 Hz • Place for high frequencies

  6. 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

  7. Locating Sound Sources • Azimuth - left/right location • Elevation - vertical location • Distance

  8. 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

  9. Elevation • Spectral Cues - effects of head and pinnae on sounds (Head Related Transfer Function)

  10. Distance Information • Sound level (for familiar sounds) • Frequency - more distant sounds lose high frequencies

  11. Distance Information • Motion Parallax - closer sounds shift location more quickly than more distant sounds • Indirect Sound - amount of reflected sound increases with distance

  12. Localization: Auditory Cortex • ITD detectors respond to specific time of arrival differences • Large receptive fields • Panoramic neurons have different firing patterns for different directions

  13. 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

  14. 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

  15. 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

  16. 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

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