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

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Presentation on theme: "Hearing Complex Sounds PSY 295 – Sensation & Perception Christopher DiMattina, PhD."— Presentation transcript:

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

3 Complex Sounds PSY Grinnell College - Fall 20122

4 Complex Sounds We have talked a lot about how the brain processes tones Real environmental sounds are a lot more complex! PSY Grinnell College - Fall 20123

5 Structure of natural sounds PSY Grinnell College - Fall 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…

6 Harmonic structure PSY Grinnell College - Fall 20125

7 The missing fundamental When you remove the fundamental frequency, you still hear it the pitch of the fundamental! PSY Grinnell College - Fall 20126

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 Grinnell College - Fall 20127

9 Web activity PSY Grinnell College - Fall 20128

10 Harmonic combination sensitivity Neurons in the auditory cortex often exhibit multi-peaked response areas with peaks at harmonic ratios PSY Grinnell College - Fall 20129

11 Harmonic combination sensitivity Response to two harmonically related tones is much greater than the response to one tone alone PSY Grinnell College - Fall

12 Marmoset calls PSY Grinnell College - Fall

13 Harmonic combination sensitivity Also seen in songbirds where songs have a harmonic structure PSY Grinnell College - Fall

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 Grinnell College - Fall

15 Timbre Different musical instruments and vowel sounds with the same fundamental frequency PSY Grinnell College - Fall

16 Web activity PSY Grinnell College - Fall

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 Grinnell College - Fall

18 Auditory cortex – ramped and damped Many neurons in auditory cortex distinguish ramped and damped tones PSY Grinnell College - Fall

19 Ramped preferring neuron PSY Grinnell College - Fall

20 Damped preferring neuron PSY Grinnell College - Fall

21 Auditory Scene Analysis PSY Grinnell College - Fall

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 Grinnell College - Fall

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

24 Different sounds have lots of spectral overlap Position on cochlea is not sufficient to separate different sounds! PSY Grinnell College - Fall

25 Stream segregation The problem of auditory stream segregation is how we break a complex acoustical waveform into different auditory objects PSY Grinnell College - Fall

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 Grinnell College - Fall

27 Web activity PSY Grinnell College - Fall

28 Bach was the master of auditory stream segregation PSY Grinnell College - Fall

29 Grouping cues Tones pop out of stream if they dont fit pattern Sounds with different timbre segregate PSY Grinnell College - Fall

30 Common onset Sounds group by onset time (different onsets separate sources) PSY Grinnell College - Fall

31 Continuity and restoration Gestalt cue of good continuation Sounds assumed to continue behind noisy occluder PSY Grinnell College - Fall

32 Perceptual restoration of tones Sound deleted and replaced with noise, sound is perceived to continue through the noise PSY Grinnell College - Fall

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 Grinnell College - Fall

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 Grinnell College - Fall

35 Context dependence The *eel fell off the car The *eel fell off the table PSY Grinnell College - Fall

36 Web activity PSY Grinnell College - Fall


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