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Hearing Complex Sounds
PSY 295 – Sensation & Perception Christopher DiMattina, PhD
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PSY 295 - Grinnell College - Fall 2012
Complex Sounds PSY Grinnell College - Fall 2012
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PSY 295 - Grinnell College - Fall 2012
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 2012
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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 Grinnell College - Fall 2012
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PSY 295 - Grinnell College - Fall 2012
Harmonic structure PSY Grinnell College - Fall 2012
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The missing fundamental
When you remove the fundamental frequency, you still hear it the pitch of the fundamental! PSY Grinnell College - Fall 2012
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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 2012
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PSY 295 - Grinnell College - Fall 2012
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Harmonic combination sensitivity
Neurons in the auditory cortex often exhibit multi-peaked response areas with peaks at harmonic ratios PSY Grinnell College - Fall 2012
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Harmonic combination sensitivity
Response to two harmonically related tones is much greater than the response to one tone alone PSY Grinnell College - Fall 2012
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PSY 295 - Grinnell College - Fall 2012
Marmoset calls PSY Grinnell College - Fall 2012
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Harmonic combination sensitivity
Also seen in songbirds where songs have a harmonic structure PSY Grinnell College - Fall 2012
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PSY 295 - Grinnell College - Fall 2012
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 2012
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PSY 295 - Grinnell College - Fall 2012
Timbre Different musical instruments and vowel sounds with the same fundamental frequency PSY Grinnell College - Fall 2012
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PSY 295 - Grinnell College - Fall 2012
Web activity PSY Grinnell College - Fall 2012
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PSY 295 - Grinnell College - Fall 2012
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 2012
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Auditory cortex – ramped and damped
Many neurons in auditory cortex distinguish ramped and damped tones PSY Grinnell College - Fall 2012
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Ramped preferring neuron
PSY Grinnell College - Fall 2012
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Damped preferring neuron
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Auditory Scene Analysis
PSY Grinnell College - Fall 2012
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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 2012
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PSY 295 - Grinnell College - Fall 2012
A world of glass Imagine vision if everything was transparent This is what your auditory system has to deal with PSY Grinnell College - Fall 2012
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Different sounds have lots of spectral overlap
Position on cochlea is not sufficient to separate different sounds! PSY Grinnell College - Fall 2012
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PSY 295 - Grinnell College - Fall 2012
Stream segregation The problem of auditory stream segregation is how we break a complex acoustical waveform into different auditory objects PSY Grinnell College - Fall 2012
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PSY 295 - Grinnell College - Fall 2012
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 2012
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PSY 295 - Grinnell College - Fall 2012
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Bach was the master of auditory stream segregation
PSY Grinnell College - Fall 2012
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PSY 295 - Grinnell College - Fall 2012
Grouping cues Tones “pop out” of stream if they don’t fit pattern Sounds with different timbre segregate PSY Grinnell College - Fall 2012
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PSY 295 - Grinnell College - Fall 2012
Common onset Sounds group by onset time (different onsets separate sources) PSY Grinnell College - Fall 2012
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Continuity and restoration
Gestalt cue of good continuation Sounds assumed to ‘continue’ behind noisy ‘occluder’ PSY Grinnell College - Fall 2012
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Perceptual restoration of tones
Sound deleted and replaced with noise, sound is perceived to continue through the noise PSY Grinnell College - Fall 2012
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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 2012
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PSY 295 - Grinnell College - Fall 2012
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 2012
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PSY 295 - Grinnell College - Fall 2012
Context dependence “The *eel fell off the car” “The *eel fell off the table” PSY Grinnell College - Fall 2012
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PSY 295 - Grinnell College - Fall 2012
Web activity PSY Grinnell College - Fall 2012
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