PSYB51H3 Lecture Notes - Neural Coding, Sine Wave, Vocal Tract

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22 Nov 2012
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Psyb51 Lec 10
SAQ: explain the temporal code of sound frequency. What is coded? How is it coded (whats the
proper scientific term for it? What are the limits of temporal coding? How could this limitation
be overcome?
- Neural frequency in firing of neurons
- Auditory nerve fires at a certain part of the phase of a sound pressure wave
- Scientific term: phase locking
o Fires whenever pressure wave goes one way or the other
- Refractory period: there is a minimum time between APs cannot fire
- Temporal coding limit volley principle
o Have diff neurons firing at the same phase but at different times diff cycles
- Several neurons share coding and still see that there are APs that are phase locked across
several neurons
Missing fundamental effect
Demo
- Increment of frequencies of harmonic sounds: multiple integers of fundamental frequency
- Harmonic sounds are something that are not uncommon, but are the sound properties of
objects vibrating in a certain way
- On the right side, see the curve that adds all the frequencies together
o Like a sine wave but is leaning leftwards this is because many sine waves were
added together
Music
- Some instruments do not have fundamental frequencies
- At first sight, music does not seem to have a purpose to our survival or evolution
o How did we adapt the ability to listen and produce music when it has no real
cause?
In theory, could use music as therapy
Music is a way to express thoughts and feelings
- Is also very mathematical
o Pythagoras: numbers and music intervals
Systematic increase when pulling string on instruments
Started looking for ratios and irregularities
Believed that music is explaining the universe
Musical notes
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- What kind of frequencies used in music?
o 25-4500hz
- Has to do with pitch: the psych aspect of sounds related mainly to the fundamental
frequency
- With pianos: lowest note = 25 hz, highest note = 4500 hz
o Have a wide range of frequencies
- Our best ability to perceive sounds is 4500 5000 hz
o Ability to hear frequencies does not match with the instruments we have
Octave: Pythagoras found out if you put a string in vibration and then cut the string and vibrate is
like the difference between keys on a piano octave
- When asking people to recognize sounds, people will confuse these sounds most often
- Octaves: tones that are very similar
- In terms of frequency, these tones are very different: is the double amount of the first key
- Ex. middle C and the next key up
o Frequency is much similar to the middle C but the tone doesn‟t sound the same
- Things very far apart sound more similar to each other
o Has nothing to do with pitch pitch means the half tone increment is more
similar to the middle C but it is not, is very different and has nothing to do with
Tone height monotonically related to frequency
- Tone chroma: goes in cycles; when starting with middle C and go up along helix to C5
within a music scale which are the notes between two C‟s, you have different chromas
- Musical helix helps understand how pitch and tone chroma are related to each other
- When playing higher ranges of the piano, is more difficult to distinguish between octaves
- Only explanation: the understanding of music and chroma is heavily dependent on
temporal coding
Chords: when two or more notes are played simultaneously
- Have CONSONANT and DISSONANT chords
- Beyond octaves have chords that sound good to us: consonant
o Ex. 2 or 3 chords/notes played together
3:2
4:3
- Chords that have more complex ratios = dissonant
o 16:15
o 45:32
- How these sound has to do with culture
o Ex. depends on whether you like jazz or classical, etc
Cultural differences:
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