2. AUDITORY PERCEPTION Pitch Perception Localization Auditory Scene Analysis

3. 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

4. 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

5. 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)

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

7. 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

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

9. 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

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

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

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

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

14. 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

15. 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

16. 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

17. 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