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Hearing Complex Sounds

Hearing Complex Sounds. PSY 295 – Sensation & Perception Christopher DiMattina , PhD. Complex Sounds. Complex Sounds. We have talked a lot about how the brain processes tones Real environmental sounds are a lot more complex!. Structure of natural sounds.

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Hearing Complex Sounds

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  1. Hearing Complex Sounds PSY 295 – Sensation & Perception Christopher DiMattina, PhD

  2. Complex Sounds PSY 295 - Grinnell College - Fall 2012

  3. Complex Sounds • We have talked a lot about how the brain processes tones • Real environmental sounds are a lot more complex! PSY 295 - Grinnell College - Fall 2012

  4. Structure of natural sounds • Many natural sounds have harmonic structure • This means that there is spectral energy at a lowest frequency called the fundamental, and energy at integer multiples of the fundamental • 200 Hz fundamental has harmonics at 400, 600, 800, etc… PSY 295 - Grinnell College - Fall 2012

  5. Harmonic structure PSY 295 - Grinnell College - Fall 2012

  6. The missing fundamental • When you remove the fundamental frequency, you still hear it the pitch of the fundamental! PSY 295 - Grinnell College - Fall 2012

  7. The missing fundamental • This happens because the harmonics all have periodicity at the fundamental frequency, so when added together the waveform has periodicity at the fundamental frequency PSY 295 - Grinnell College - Fall 2012

  8. Web activity • http://sites.sinauer.com/wolfe3e/chap10/missingfundF.htm PSY 295 - Grinnell College - Fall 2012

  9. Harmonic combination sensitivity • Neurons in the auditory cortex often exhibit multi-peaked response areas with peaks at harmonic ratios PSY 295 - Grinnell College - Fall 2012

  10. Harmonic combination sensitivity • Response to two harmonically related tones is much greater than the response to one tone alone PSY 295 - Grinnell College - Fall 2012

  11. Marmoset calls PSY 295 - Grinnell College - Fall 2012

  12. Harmonic combination sensitivity • Also seen in songbirds where songs have a harmonic structure PSY 295 - Grinnell College - Fall 2012

  13. Timbre • Can define a tone by its pitch and loudness • Complex sounds have many spectral components • Its qualitative character depends on it spectral shape PSY 295 - Grinnell College - Fall 2012

  14. Timbre • Different musical instruments and vowel sounds with the same fundamental frequency PSY 295 - Grinnell College - Fall 2012

  15. Web activity • http://sites.sinauer.com/wolfe3e/chap10/timbreF.htm PSY 295 - Grinnell College - Fall 2012

  16. Attack and Decay • We are sensitive not only to spectral content but temporal properties • Attack – part of sound where amplitude increases • Decay – part of sound where amplitude decreases PSY 295 - Grinnell College - Fall 2012

  17. Auditory cortex – ramped and damped • Many neurons in auditory cortex distinguish ramped and damped tones PSY 295 - Grinnell College - Fall 2012

  18. Ramped preferring neuron PSY 295 - Grinnell College - Fall 2012

  19. Damped preferring neuron PSY 295 - Grinnell College - Fall 2012

  20. Auditory Scene Analysis PSY 295 - Grinnell College - Fall 2012

  21. Difference between hearing and vision • Light waves from different objects block each otherif objects are displaced in depth (occlusion) • Sound waves from different sources add together PSY 295 - Grinnell College - Fall 2012

  22. A world of glass • Imagine vision if everything was transparent • This is what your auditory system has to deal with PSY 295 - Grinnell College - Fall 2012

  23. Different sounds have lots of spectral overlap • Position on cochlea is not sufficient to separate different sounds! PSY 295 - Grinnell College - Fall 2012

  24. Stream segregation • The problem of auditory stream segregation is how we break a complex acoustical waveform into different auditory objects PSY 295 - Grinnell College - Fall 2012

  25. Example • When tones are played rapidly at two alternating frequencies, one perceives a single warbling source • However, when frequencies are sufficiently different, one hears two separate streams PSY 295 - Grinnell College - Fall 2012

  26. Web activity • http://sites.sinauer.com/wolfe3e/chap10/audstreamsegF.htm PSY 295 - Grinnell College - Fall 2012

  27. Bach was the master of auditory stream segregation • http://www.youtube.com/watch?v=ipzR9bhei_o PSY 295 - Grinnell College - Fall 2012

  28. Grouping cues • Tones “pop out” of stream if they don’t fit pattern • Sounds with different timbre segregate PSY 295 - Grinnell College - Fall 2012

  29. Common onset • Sounds group by onset time (different onsets  separate sources) PSY 295 - Grinnell College - Fall 2012

  30. Continuity and restoration • Gestalt cue of good continuation • Sounds assumed to ‘continue’ behind noisy ‘occluder’ PSY 295 - Grinnell College - Fall 2012

  31. Perceptual restoration of tones • Sound deleted and replaced with noise, sound is perceived to continue through the noise PSY 295 - Grinnell College - Fall 2012

  32. Perceptual restoration of speech • Deleting parts of speech and replacing them with noise, cough, etc.. leads to completion • Often people cannot say which segment was deleted! PSY 295 - Grinnell College - Fall 2012

  33. Restoration in birds • Starlings trained to peck when they heard a difference between two starling song segments • More likely to hear difference with silent gap • More likely to fill in familiar rather than unfamiliar songs PSY 295 - Grinnell College - Fall 2012

  34. Context dependence • “The *eel fell off the car” • “The *eel fell off the table” PSY 295 - Grinnell College - Fall 2012

  35. Web activity • http://sites.sinauer.com/wolfe3e/chap10/restorationF.htm PSY 295 - Grinnell College - Fall 2012

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