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Slide 2 Hearing Complex Sounds PSY 295 Sensation & Perception Christopher DiMattina, PhD Slide 3 Complex Sounds PSY 295 - Grinnell College - Fall 20122 Slide 4 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 20123 Slide 5 Structure of natural sounds PSY 295 - Grinnell College - Fall 20124 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 Slide 6 Harmonic structure PSY 295 - Grinnell College - Fall 20125 Slide 7 The missing fundamental When you remove the fundamental frequency, you still hear it the pitch of the fundamental! PSY 295 - Grinnell College - Fall 20126 Slide 8 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 20127 Slide 9 Web activity http://sites.sinauer.com/wolfe3e/chap10/missingfundF.htm PSY 295 - Grinnell College - Fall 20128 Slide 10 Harmonic combination sensitivity Neurons in the auditory cortex often exhibit multi-peaked response areas with peaks at harmonic ratios PSY 295 - Grinnell College - Fall 20129 Slide 11 Harmonic combination sensitivity Response to two harmonically related tones is much greater than the response to one tone alone PSY 295 - Grinnell College - Fall 201210 Slide 12 Marmoset calls PSY 295 - Grinnell College - Fall 201211 Slide 13 Harmonic combination sensitivity Also seen in songbirds where songs have a harmonic structure PSY 295 - Grinnell College - Fall 201212 Slide 14 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 201213 Slide 15 Timbre Different musical instruments and vowel sounds with the same fundamental frequency PSY 295 - Grinnell College - Fall 201214 Slide 16 Web activity http://sites.sinauer.com/wolfe3e/chap10/timbreF.htm PSY 295 - Grinnell College - Fall 201215 Slide 17 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 201216 Slide 18 Auditory cortex ramped and damped Many neurons in auditory cortex distinguish ramped and damped tones PSY 295 - Grinnell College - Fall 201217 Slide 19 Ramped preferring neuron PSY 295 - Grinnell College - Fall 201218 Slide 20 Damped preferring neuron PSY 295 - Grinnell College - Fall 201219 Slide 21 Auditory Scene Analysis PSY 295 - Grinnell College - Fall 201220 Slide 22 Difference between hearing and vision Light waves from different objects block each other if objects are displaced in depth (occlusion) Sound waves from different sources add together PSY 295 - Grinnell College - Fall 201221 Slide 23 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 201222 Slide 24 Different sounds have lots of spectral overlap Position on cochlea is not sufficient to separate different sounds! PSY 295 - Grinnell College - Fall 201223 Slide 25 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 201224 Slide 26 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 201225 Slide 27 Web activity http://sites.sinauer.com/wolfe3e/chap10/audstreamsegF.htm PSY 295 - Grinnell College - Fall 201226 Slide 28 Bach was the master of auditory stream segregation http://www.youtube.com/watch?v=ipzR9bhei_o PSY 295 - Grinnell College - Fall 201227 Slide 29 Grouping cues Tones pop out of stream if they dont fit pattern Sounds with different timbre segregate PSY 295 - Grinnell College - Fall 201228 Slide 30 Common onset Sounds group by onset time (different onsets separate sources) PSY 295 - Grinnell College - Fall 201229 Slide 31 Continuity and restoration Gestalt cue of good continuation Sounds assumed to continue behind noisy occluder PSY 295 - Grinnell College - Fall 201230 Slide 32 Perceptual restoration of tones Sound deleted and replaced with noise, sound is perceived to continue through the noise PSY 295 - Grinnell College - Fall 201231 Slide 33 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 201232 Slide 34 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 201233 Slide 35 Context dependence The *eel fell off the car The *eel fell off the table PSY 295 - Grinnell College - Fall 201234 Slide 36 Web activity http://sites.sinauer.com/wolfe3e/chap10/restorationF.htm PSY 295 - Grinnell College - Fall 201235