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Lecture 10

PSYB51 Lecture 10.docx

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Matthias Neimier

PSYB51 - Lecture 10 Explain the temporal code of sound frequency. What is coded? How is it coded (what’s the proper scientific term for it)? What are the limits of temporal coding? How could this limitation be overcome? - Amplitude, phase, frequency-> Phase-locking - Limits of temporal coding neurons will fire with frequency of less than 1000 hertz because they simply cannot fire at such a fast rate - The volley principle: one neuron fires and the next takes over and the entire population of the neurons will represent the frequency in its firing pattern Complex Sounds – Harmonics  Missing fundamentals – Timbre  Timbre aftereffect  Attack & decay  Harmonics – Lowest frequency of harmonic spectrum: Fundamental frequency (any multiple of something else. The next frequency sounded with the next one has double frequency, and the third harmonic has triple frequency, etc.) – Auditory system is acutely sensitive to natural relationships between harmonics – e.g. vowels – Missing-fundamental effect (the next sound wave deletes the next harmonic) Missing fundamental(x1) is not/barely noticed. • More harmonics can be missing.
 • How come? Missing fundamental harmonic: 250 Hz • 2 , 3rd & 4 thharmonic overlap in peaks every 4 ms • Added up they yield a 
 fluctuation in energy at 250 Hz • Temporal coding of frequency  Timbre: Psychological sensation by which a listener can judge that two sounds that have the same loudness and pitch are dissimilar; conveyed by harmonics and other high frequencies – Perception of timbre depends on context in which sound is heard (when you sing, you can hear the vowel-> eg. E has a high harmonic) – Experiment by Summerfield et al. (1984) -> after hearing what the synthesizer produced, 
 • ―Timbre contrast‖ or ―timbre aftereffect‖  Summerfieldetal.‘s (1984) ―timbre after effect‖ The peaks on the graph are very typical for the vowel E Usually 3 or more peaks are in the power spectrum called FORMANCE (fingerprints of vowels)  Attack and decay of sound – Attack: Part of a sound during which amplitude increases (onset) – Decay: Part of a sound during which amplitude decreases (offset) Auditory Scene Analysis
 (being able to hear sounds in rich environment; to tell which sounds are coming from which sources and which belong to each other in a group) – Segregating sound sources – Grouping
 – The ventriloquist effect  What happens in natural situations? – Acoustic environment can be a busy place – Multiple sound sources – How does auditory system sort out these sources? – Source segregation, or auditory scene analysis  A number of strategies to segregate sound sources – Spatial separation between sounds (ex. time difference to tell the frog is sounding from the left; bird is sitting on the right ) ; motion parallax (the ribbit sound of the frog sitting on the ground will move to your ears and will change as you walk around but the sound of the bird will not change if it‘s sitting far away to begin with) – Separation on basis of sounds‘ spectral or temporal qualities – Auditory stream segregation: Perceptual organization of a complex acoustic signal into separate auditory events for which each stream is heard as a separate event – Gestalt law: ―similarity‖ Gestalt: German for ―form‖. In perception a term introduced by a school of thought stressing that the perceptual whole could be greater than the sum of its parts.  Grouping by timbre – Tones that have increasing and decreasing frequencies, or tones that deviate from rising/falling pattern ―pop out‖ of sequence  Grouping by onset – Harmonics of speech sound or music – Grouping different harmonics into a single complex tone (you hear harmonics in one tone because they onset at the same time) – Rasch (1987) showed that it is much easier to distinguish two notes from one another when onset of one precedes onset of other by very short time – Gestalt law of common fate – Does the bottle break? Eg. When you hear a bottle falling somewhere, you can hear whether the bottle is bouncing in its entirety or whether the fall was too deep and falling into shards and pieces  Spectogram: A pattern for sound analysis that provides a 3D display of intensity as a function of time and frequency – E.g., bouncing/breaking bottle (the problem with the graph is it doesn‘t display time) Multi sensory integration: vision (usually) helps audition • Ventriloquist effect: An audio- visual illusion in which sound is misperceived as emanating from a source that can be seen to be moving appropriately when it actually emanates from a • ventriloquist_comedian_kenny_warren_on_robert_kle in_time/ Continuity and Restoration Effects
 – Gestalt principle of good continuation for simple sounds.
 – ... and for complex ones  How do we know that listeners really hear a sound as continuous? – Principle of good continuation: In spite of interruptions, one can still ―hear‖ sound – Experiments that use signal detection task (e.g., Kluender and Jenison) suggest that at some point restored missing sounds are encoded in brain as if they were actually present! Restoration of complex sound,(e.g.,music, speech) – ―Higher-order‖ sources of information, not just auditory information
 • ―The *eel fell off the car.‖ (wheel) • ―... the table.‖ (meal)  Noise helps comprehension.
  ―The mailman brought the letter.‖-> the blue in the picture means silence Amodal completion and modal completion What‘s Special About Music?
 – What‘s the difference between tone height and tone chroma? – Chords
 – Melody  Music is a way to express thoughts and emotions
 (thus, we enjoy music because it gives us certain emotions) – Pythagoras: Numbers and music intervals
 – Some clinical psychologists practice music therapy  Musical notes
 – Sounds of music extend across a frequency range from about 25 to 4500 Hz – Pitch: the psychological aspect of sounds related mainly to the fundamental frequency  Octave: The interval between two sound frequencies having a ratio of 2:1 – Example: Middle C (C ) has a fundamental frequency of 261.6 Hz; notes that are one 4 octave from middle C are 130.8 Hz (C ) and 523.2 Hz 
 (C ) 3 5 – C (130.8 Hz) sounds more similar to C (261.6 
 Hz) than to E (164.8 Hz) 3 4 3 – There is more to musical pitch than just frequency  Tone height: A sound quality corresponding to the level of pitch. Tone height is monotonically related to frequency  Tone chroma: A sound quality shared by tones that have the same octave interval 
 – Each note on the musical scale (A–G) has a different chroma • Musical helix: Can help to visualize musical pitch  Musical instruments: Produce notes below 4 kHz – Listeners: Great difficulty perceiving octave relationships between tones when one or both – Chords: Created when two or more notes are played simultaneously – Consonant: Have simple ratios of note frequencies (3:2, 4:3) – Dissonant: Less elegant ratios of note frequencies (16:15, 45:32)  Cultural differences
 – Some relationships between
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